{"gene":"KCNK9","run_date":"2026-06-10T02:59:49","timeline":{"discoveries":[{"year":2000,"finding":"TASK-3 (KCNK9) encodes a time-independent, non-inactivating K+-selective background current. Mutation of histidine at position 98 to aspartate abolished extracellular pH sensitivity, identifying His98 as the critical pH sensor.","method":"Heterologous expression in COS-7 cells, whole-cell and single-channel patch-clamp, site-directed mutagenesis","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 1 / Strong — reconstitution in heterologous cells with mutagenesis, independently replicated in a second paper the same year (PMID:10747866)","pmids":["10734076","10747866"],"is_preprint":false},{"year":2000,"finding":"His98, located at the outer pore adjacent to the selectivity filter, is an essential component of the extracellular pH sensor; substitution of His98 with asparagine or tyrosine abolished pH sensitivity. Single-channel recordings in HEK293 cells showed inwardly rectifying I-V relationship with open probability increasing markedly with depolarization.","method":"Xenopus oocyte expression, HEK293 cell-attached patch-clamp, site-directed mutagenesis","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 1 / Strong — in vitro reconstitution with mutagenesis, replicated across two independent labs (PMID:10734076 and PMID:10747866)","pmids":["10747866"],"is_preprint":false},{"year":2001,"finding":"TASK-1 and TASK-3 form functional heterodimers when co-expressed in Xenopus oocytes. A tandem-linked TASK-3/TASK-1 construct yielded currents with intermediate pH sensitivity and ruthenium red insensitivity (TASK-1-like). Epitope-tagged channels localized primarily to the plasma membrane in mammalian cells.","method":"Xenopus oocyte co-expression, tandem-linked constructs, two-electrode voltage clamp, immunofluorescence localization in mammalian cells","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 1-2 / Strong — functional heterodimer reconstitution in two systems, tandem construct validation, replicated by multiple subsequent labs","pmids":["11733509"],"is_preprint":false},{"year":2002,"finding":"A six-residue sequence at the beginning of the cytoplasmic C-terminus (interface of final transmembrane domain and C-terminus) is required for both volatile anesthetic (halothane) activation and neurotransmitter (TRH) inhibition of TASK-3; mutations in this region virtually abolished both effects. The identified phosphorylation site within this region was not required for modulation.","method":"Site-directed mutagenesis, heterologous expression, whole-cell electrophysiology","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 1 / Moderate — reconstitution with systematic mutagenesis, multiple mutants tested with two distinct modulators, single lab","pmids":["11886861"],"is_preprint":false},{"year":2002,"finding":"TASK-3 C-terminal domain interacts with 14-3-3 adapter proteins via a C-terminal RRx(S/T)x motif. This interaction promotes surface membrane expression; deletion of a single C-terminal amino acid abolished 14-3-3 binding and strongly reduced macroscopic currents. Co-injection of 14-3-3ζ increased TASK-3 current by ~70% in oocytes. TASK-1 and 14-3-3 co-immunoprecipitated from synaptic membranes.","method":"Yeast two-hybrid, co-immunoprecipitation, Xenopus oocyte voltage clamp, GFP surface expression assay in HEK293 cells, truncation/point mutagenesis","journal":"The Journal of physiology","confidence":"High","confidence_rationale":"Tier 1-2 / Strong — multiple orthogonal methods (Y2H, Co-IP, electrophysiology, surface expression), independently confirmed in subsequent trafficking studies","pmids":["12433946"],"is_preprint":false},{"year":2002,"finding":"TASK-3 dominates the background K+ conductance of rat adrenal glomerulosa cells. The pharmacological profile of native glomerulosa current (ruthenium red sensitivity in micromolar range, weak acid sensitivity) matches TASK-3, and TASK-3 current is inhibited by AT1a angiotensin II receptor stimulation when co-expressed.","method":"Northern blot, quantitative RT-PCR, Xenopus oocyte electrophysiology, pharmacological characterization","journal":"Molecular endocrinology","confidence":"Medium","confidence_rationale":"Tier 2-3 / Moderate — pharmacological matching of native current to cloned channel, functional angiotensin II inhibition in reconstituted system, single lab","pmids":["11875121"],"is_preprint":false},{"year":2003,"finding":"Oncogenic functions of TASK3 (KCNK9) — promoting proliferation in low serum, resistance to apoptosis, and tumor growth in nude mice — require intact K+ channel function. A pore mutation (G95E) abolished both K+ current and oncogenic activity. G95E acts as a dominant-negative, suppressing wild-type TASK3 current and tumorigenicity when co-expressed.","method":"Site-directed mutagenesis, patch-clamp electrophysiology, cell proliferation assays, apoptosis assays, nude mouse xenograft","journal":"Proceedings of the National Academy of Sciences of the United States of America","confidence":"High","confidence_rationale":"Tier 1-2 / Strong — mutagenesis directly links channel activity to oncogenic function, dominant-negative validation, in vivo xenograft, multiple orthogonal assays","pmids":["12782791"],"is_preprint":false},{"year":2003,"finding":"Ruthenium red inhibits TASK-3 by simultaneously binding glutamate 70 (Glu70) on both subunits of the dimer. Mutation of Glu70 to Arg or Cys in either subunit of a tandem construct abolished RR inhibition. The Hill coefficient of ~1.0 indicates one RR molecule bridges both subunits. Introducing Glu at position 70 of TASK-1 (K70E) conferred RR sensitivity.","method":"Site-directed mutagenesis of tandem constructs, Xenopus oocyte electrophysiology, pharmacological dose-response analysis","journal":"Molecular pharmacology","confidence":"High","confidence_rationale":"Tier 1 / Strong — systematic mutagenesis of both subunits in tandem constructs with gain-of-function in TASK-1, mechanistically rigorous","pmids":["12606773"],"is_preprint":false},{"year":2004,"finding":"TASK-1/TASK-3 heterodimers are expressed in native hypoglossal motoneurons. Co-immunoprecipitation from transfected mammalian cell membranes confirmed physical association. A dominant-negative TASK-1(Y191F) suppressed TASK-3 currents. Heteromeric channels display intermediate pH sensitivity (pK ~7.3) and are activated (not inhibited) by high isoflurane, matching native motoneuron TASK currents.","method":"Co-immunoprecipitation, dominant-negative suppression, tandem-linked heterodimer electrophysiology, native neuron patch-clamp, pharmacological profiling","journal":"The Journal of neuroscience","confidence":"High","confidence_rationale":"Tier 2 / Strong — reciprocal Co-IP, dominant-negative, tandem construct, native cell validation, multiple orthogonal methods","pmids":["15282272"],"is_preprint":false},{"year":2004,"finding":"Native 38-pS K+ channels in cerebellar granule neurons include both homomeric TASK-3 and heteromeric TASK-1/TASK-3 channels, identified by differential sensitivity to ruthenium red and extracellular pH changes matching cloned homomers and heterodimers.","method":"Single-channel patch-clamp of cultured cerebellar granule neurons and COS-7-expressed cloned channels, pharmacological profiling with ruthenium red and pH","journal":"The Journal of physiology","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — direct single-channel comparison between native and cloned channels, single lab, pharmacological but not molecular validation in native tissue","pmids":["14678492"],"is_preprint":false},{"year":2006,"finding":"Glutamate 70 (Glu70) in the extracellular loop of TASK-3 mediates sensitivity to divalent cations (Ca2+, Mg2+) and polycations (spermine, ruthenium red). Replacing Glu70 with Lys or Arg abolished divalent cation sensitivity; the reverse mutation in TASK-1 (K70E) induced this sensitivity. Spermine and ruthenium red also decrease open probability likely by binding Glu70.","method":"Site-directed mutagenesis, HEK293 cell single-channel and whole-cell electrophysiology, charge-swap experiments","journal":"The Journal of physiology","confidence":"High","confidence_rationale":"Tier 1 / Strong — systematic mutagenesis with gain-of-function in TASK-1 and loss-of-function in TASK-3, multiple orthogonal pharmacological agents","pmids":["16513667"],"is_preprint":false},{"year":2006,"finding":"Transcription of TASK-3 in cerebellar granule neurons is regulated by membrane depolarization through Ca2+ entry via L-type channels and the downstream effector calcineurin. Blocking L-type Ca2+ channels or calcineurin abrogated TASK-3 mRNA and protein upregulation and the IKso conductance, causing hyperexcitability.","method":"In vitro neuronal culture in depolarizing/non-depolarizing KCl conditions, pharmacological blockade of L-type channels and calcineurin, RT-PCR, patch-clamp","journal":"The Journal of biological chemistry","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — pharmacological epistasis identifying calcineurin pathway, functional current measurements, single lab","pmids":["16864570"],"is_preprint":false},{"year":2007,"finding":"Di-acidic motif EDE in the proximal C-terminus of TASK-3 is required for efficient ER export and surface membrane expression. Mutation of the two glutamate residues (ADA mutant) markedly reduced surface expression and retained the channel in the ER. ER export of TASK-3 requires COPII machinery (blocked by dominant-negative Sar1H79G).","method":"Luminometric surface expression assay, Xenopus oocyte voltage clamp, live-cell GFP imaging in COS-7 cells, Sar1 dominant-negative co-expression, chimeric constructs","journal":"Traffic","confidence":"High","confidence_rationale":"Tier 2 / Strong — multiple orthogonal methods (surface assay, electrophysiology, live imaging, dominant-negative), mechanistically rigorous ER export pathway","pmids":["17547699"],"is_preprint":false},{"year":2007,"finding":"Protein kinase C (PKCα) phosphorylates Thr341 in the C-terminus of human TASK3, thereby reducing channel current. Gαq-coupled M3 muscarinic receptor inhibition of TASK3 occurs through a direct action of Gαq on the channel (not through PKC), while PKC activation opposes and limits the duration of Gq-mediated inhibition.","method":"Site-directed mutagenesis of phosphorylation site, siRNA knockdown of PKCα, selective PKC inhibitors, Gαq antagonist (YM-254890), whole-cell patch-clamp","journal":"Molecular pharmacology","confidence":"High","confidence_rationale":"Tier 1-2 / Strong — mutagenesis of phosphorylation site, gene silencing, selective antagonist, multiple orthogonal approaches in single lab","pmids":["17374744"],"is_preprint":false},{"year":2008,"finding":"The Birk Barel syndrome missense mutation G236R in the maternal copy of KCNK9 fully abolishes channel currents both when functioning as a homodimer and as a heterodimer with K2P3.1 (TASK-1), establishing loss-of-function as the disease mechanism.","method":"Electrophysiological characterization of mutant channels in heterologous expression system, genetic mapping","journal":"American journal of human genetics","confidence":"High","confidence_rationale":"Tier 1-2 / Strong — direct electrophysiological demonstration of loss-of-function in both homo- and heterodimeric configurations, disease-causing variant","pmids":["18678320"],"is_preprint":false},{"year":2008,"finding":"The M1P1 extracellular loop of TASK-3 lies close to the pore and regulates channel activity. Disulfide bond formation between Cys substitutions at Glu70 (M1P1 loop) and His98 (pore) in tandem constructs confirms their spatial proximity. The M1P1 loop also participates in pH regulation of TASK-3.","method":"Site-directed mutagenesis with cysteine substitutions, tandem-fixed constructs, dithiothreitol/cadmium probing, loop-swap chimeras, patch-clamp","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 1 / Moderate — disulfide crosslinking between engineered cysteines, gain-of-function with cadmium, chimera experiments, single lab","pmids":["18417474"],"is_preprint":false},{"year":2009,"finding":"TASK-3 surface expression is controlled by 14-3-3 binding masking a tri-basic COPI retention signal (KRR) in the C-terminus. When 14-3-3 binding is disabled, KRR is exposed and binds COPI coatomer, retaining the channel in the Golgi. TASK-3 also has an independent di-basic N-terminal retention signal (KR). 14-3-3 binding does not affect dimeric assembly.","method":"Mutational analysis in Xenopus oocytes, mammalian cells and yeast; GST pulldown of COPI with KRR motif; GFP-tagged channel localization; dominant-negative suppression of dimerization","journal":"The Journal of physiology","confidence":"High","confidence_rationale":"Tier 1-2 / Strong — GST pulldown identifies COPI binding, mutagenesis in multiple systems, subcellular localization directly linked to trafficking mechanism","pmids":["19139046"],"is_preprint":false},{"year":2009,"finding":"TASK-1/TASK-3 heteromers are the major oxygen-sensitive background K+ channels in rat carotid body glomus cells, contributing ~75% of TASK-like current. Discrimination among TASK-1, TASK-3, and TASK-1/3 heteromers was achieved by comparing single-channel conductances in defined Mg2+ conditions and ruthenium red sensitivity in native cells vs. cloned channels.","method":"Single-channel patch-clamp of native carotid body cells and cloned channels in outside-out/cell-attached configuration, pharmacological profiling with ruthenium red and methanandamide","journal":"The Journal of physiology","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — rigorous biophysical comparison of native vs. cloned channel properties, pharmacological orthogonal probes, single lab","pmids":["19403596"],"is_preprint":false},{"year":2009,"finding":"TASK-3 voltage-dependent gating involves a cytoplasmic gate in addition to the selectivity filter. Mutations in M2 (N133A) and M4 (A237T) increase open probability and shift voltage dependence, while mutating conserved hinge glycines (G117A, G231A) decreases open probability. Two routes out of the open state indicate dual gating at selectivity filter and cytoplasmic mouth.","method":"Two-electrode voltage clamp, single-channel recording, kinetic modeling, site-directed mutagenesis","journal":"The Journal of physiology","confidence":"Medium","confidence_rationale":"Tier 1 / Moderate — systematic mutagenesis with single-channel analysis and kinetic modeling, single lab","pmids":["19703964"],"is_preprint":false},{"year":2011,"finding":"Protein kinase A (PKA/cAMP-dependent protein kinase) phosphorylates Ser373 in the C-terminus of TASK-3 (K2P9.1), and this phosphorylation enables 14-3-3 binding to overcome ER retention by βCOP, thus promoting forward trafficking to the plasma membrane.","method":"In vitro phosphorylation assays, bioinformatics candidate selection, electrophysiology in HEK293 cells, cell surface GFP assay","journal":"The Journal of biological chemistry","confidence":"Medium","confidence_rationale":"Tier 1-2 / Moderate — in vitro kinase assay plus functional surface expression assay, single lab, identifies specific phosphorylation site","pmids":["21357689"],"is_preprint":false},{"year":2011,"finding":"Met159 in TASK-3 is essential for volatile anesthetic activation and contributes to the anesthetic binding site. Covalent modification of M159C by NEM irreversibly activated the channel and rendered it resistant to inhibition by both acidic pH and active Gαq protein. A single modified subunit in a wild-type/M159C tandem is sufficient for activation, indicating cross-talk between subunits.","method":"Site-directed mutagenesis (M159C, M159W, M159F), cysteine-reactive NEM modification, tandem dimers, electrophysiology in Fischer rat thyroid cells (Ussing chamber)","journal":"Molecular pharmacology","confidence":"High","confidence_rationale":"Tier 1 / Strong — covalent modification strategy with mutagenesis and tandem constructs, mechanistically rigorous, identifies specific residue","pmids":["22147752"],"is_preprint":false},{"year":2012,"finding":"N-linked glycosylation of TASK-3 (K2P9.1) occurs at the conserved consensus site; however, disruption of glycosylation causes only a small reduction in cell surface channels with no detectable functional change in K+ current, in contrast to TASK-1 where glycosylation loss significantly reduces surface expression and current.","method":"Flow cytometry surface expression assay, patch-clamp, site-directed mutagenesis of glycosylation site, tunicamycin treatment","journal":"The Journal of biological chemistry","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — multiple orthogonal methods, clear functional contrast with TASK-1, single lab","pmids":["23250752"],"is_preprint":false},{"year":2013,"finding":"The Birk Barel G236R mutant TASK-3 produces a small, inwardly rectifying current (not zero current) with altered responses to extracellular acidification, zinc, and Gαq-coupled muscarinic receptors compared to wild-type. A gain-of-function second mutation A237T and the NSAID flufenamic acid partially restore outward current through G236R channels.","method":"Whole-cell electrophysiology of wild-type and G236R mutant TASK-3, pharmacological profiling, double mutants","journal":"Molecular pharmacology","confidence":"Medium","confidence_rationale":"Tier 1-2 / Moderate — electrophysiological characterization of disease mutant with pharmacological rescue, single lab","pmids":["24342771"],"is_preprint":false},{"year":2013,"finding":"TASK-3 channels are present in mitochondria of aldosterone-producing zona glomerulosa cells, confirmed by yeast two-hybrid, immunoprecipitation, and electron microscopy. Genetic deletion of TASK-3 from mice disrupts mitochondrial morphology, mitochondrial membrane potential, and aldosterone production without changing plasma membrane potential of glomerulosa cells.","method":"Yeast two-hybrid, immunoprecipitation, electron microscopy, mitochondrial membrane potential measurements, aldosterone assays in TASK-3 knockout mice","journal":"Hypertension","confidence":"High","confidence_rationale":"Tier 1-2 / Strong — three orthogonal methods confirming mitochondrial localization, functional KO phenotype, mechanistically links mitochondrial TASK-3 to aldosterone regulation","pmids":["28630209"],"is_preprint":false},{"year":2014,"finding":"TASK-3 channels are highly enriched in a subpopulation of TRPM8-positive cold-sensitive neurons. Blockade or genetic knockout of TASK-3 reduces the thermal threshold of cold neurons and causes hypersensitivity to cold in mice, establishing TASK-3 as a modulator of thermosensation in peripheral cold receptors.","method":"BAC transgenesis, FACS purification of TRPM8 neurons, molecular profiling, pharmacological blockade, TASK-3 knockout mouse behavioral assays","journal":"Cell reports","confidence":"High","confidence_rationale":"Tier 2 / Strong — genetic KO with specific behavioral phenotype validated with pharmacological blockade, molecular enrichment analysis","pmids":["25199828"],"is_preprint":false},{"year":2014,"finding":"Neurotensin (NT) excites dentate gyrus granule cells via NTS1 receptor-mediated inhibition of TASK-3 K+ channels through direct coupling of Gαq/11 to TASK-3 (not via PLC, IP3-Ca2+, or PKC). Co-immunoprecipitation showed NTS1 activation induced physical association of Gαq/11 with TASK-3.","method":"Whole-cell patch-clamp in brain slices, pharmacological dissection, co-immunoprecipitation, receptor-specific antagonists","journal":"Cerebral cortex","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — Co-IP demonstrating direct Gαq/TASK-3 association, combined with pharmacological pathway dissection, single lab","pmids":["25405940"],"is_preprint":false},{"year":2015,"finding":"Breathing stimulants PKTHPP, A1899, and doxapram inhibit TASK-3 by binding within the intracellular pore region. Mutagenesis identified residues L122 and G236 as critical for drug binding; L122D and G236D mutations increased IC50 >1000-fold. These same mutations conferred resistance to all three compounds.","method":"Homology modeling, molecular docking, site-directed mutagenesis, Ussing chamber electrophysiology in Fischer rat thyroid monolayers","journal":"Molecular pharmacology","confidence":"Medium","confidence_rationale":"Tier 1 / Moderate — mutagenesis with functional readout, supported by molecular docking, single lab, three distinct compounds converging on same site","pmids":["26268529"],"is_preprint":false},{"year":2018,"finding":"TWIK-1 physically associates with TASK-3 in dentate gyrus granule cells (DGGCs) and in COS-7 cells. TWIK-1/TASK-3 heterodimeric channels display outwardly rectifying currents and contribute to intrinsic excitability of DGGCs. Neurotensin-NTS1 signaling depolarizes DGGCs by inhibiting TWIK-1/TASK-3 heterodimeric channels.","method":"Co-immunoprecipitation from mouse hippocampus and COS-7 cells, shRNA knockdown of each subunit, patch-clamp of DGGCs","journal":"Experimental & molecular medicine","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — Co-IP from native tissue, shRNA-mediated functional dissection, single lab","pmids":["30416196"],"is_preprint":false},{"year":2019,"finding":"KCC2 interacts with TASK-3 (KCNK9) channels and is required for their membrane expression. KCC2 knockdown in rat dentate gyrus neurons reduces TASK-3 surface expression, decreases leak K+ currents, and depolarizes resting membrane potential, leading to increased neuronal excitability and altered network rhythmogenesis.","method":"Co-immunoprecipitation of KCC2 and TASK-3, shRNA knockdown of KCC2, patch-clamp, subcellular fractionation, chemogenetic rescue","journal":"Cell reports","confidence":"High","confidence_rationale":"Tier 2 / Strong — Co-IP demonstrates interaction, KD shows functional consequence on TASK-3 surface expression and excitability, chemogenetic rescue validates specificity","pmids":["31269453"],"is_preprint":false},{"year":2019,"finding":"Doxapram inhibits human TASK-3 (hKCNK9) and TASK-1 channels with equal potency (unlike mouse channels where it is TASK-1-selective). Inhibition is attenuated by C-terminus truncation or mutations of hydrophobic pore-lining residues, while an extracellular zinc binding site is not affected. The (+)-enantiomer GAL-054 is more potent than doxapram; the (−)-enantiomer GAL-053 has little effect.","method":"Whole-cell patch-clamp in tsA201 cells, site-directed mutagenesis of pore residues, chirally separated enantiomers, species comparison (human vs. mouse)","journal":"Acta physiologica","confidence":"Medium","confidence_rationale":"Tier 1-2 / Moderate — mutagenesis identifies pore residues for inhibition, enantiomer structure-activity analysis, single lab","pmids":["31423744"],"is_preprint":false},{"year":2020,"finding":"Withaferin A (WFA) inhibits TASK-3 channels in a dose-dependent, voltage-independent manner. Molecular docking and mutagenesis identified F125 and L197 as critical residues for WFA binding; F125A, L197V, and double mutant markedly reduced WFA inhibition. The cytotoxic effect of WFA in MDA-MB-231 cells depends on TASK-3 expression.","method":"Patch-clamp in HEK-293 cells, molecular docking, site-directed mutagenesis, TASK-3 overexpression and shRNA knockdown in cancer cells, cell viability assays","journal":"Biomedicine & pharmacotherapy","confidence":"Medium","confidence_rationale":"Tier 1-2 / Moderate — mutagenesis identifies binding residues, combined with functional cancer cell assays, single lab","pmids":["32563149"],"is_preprint":false},{"year":2022,"finding":"KCNK9 imprinting syndrome variants cause both gain and loss of TASK-3 channel conductance, but the most consistent functional impact is altered channel regulation (loss of regulatory control). An additional mutational hotspot was identified at p.Arg131. 3D protein modeling and in vitro electrophysiology define the structural basis of variant effects.","method":"In vitro electrophysiology of 15 novel KCNK9 variants, computational 3D molecular mechanics and dynamics, clinical genetics, facial phenotyping","journal":"Genome medicine","confidence":"Medium","confidence_rationale":"Tier 1-2 / Moderate — multiple variants characterized electrophysiologically with structural modeling, but no single orthogonal structural method validated","pmids":["35698242"],"is_preprint":false},{"year":2024,"finding":"Cryo-EM structures of human TASK-3 at neutral and acidic pH revealed that extracellular acidification drives C-type inactivation through selectivity filter rearrangement: the SF mouth dilates while a hydrophobic gate blocks the pore. His98 protonation shifts the equilibrium toward the inactivated state by engaging a cation-π interaction with Trp78, as confirmed by MD simulations and mutagenesis.","method":"Cryo-EM structural determination at two pH values, molecular dynamics simulations, site-directed mutagenesis of His98 and Trp78, electrophysiology","journal":"Proceedings of the National Academy of Sciences of the United States of America","confidence":"High","confidence_rationale":"Tier 1 / Strong — high-resolution cryo-EM structures at two pH states, supported by MD simulations and mutagenesis validating mechanistic model","pmids":["38630723"],"is_preprint":false},{"year":2024,"finding":"Cryo-EM structures of human TASK-1 and TASK-3 (including the G236R KIS variant) reveal a conserved lower X-gate gating mechanism. The G236R substitution disrupts the X-gate, providing structural explanation for loss-of-function in KCNK9 imprinting syndrome. Combined functional studies confirmed X-gate conformational changes underlie pH-dependent inhibition.","method":"Cryo-EM structure determination of wild-type TASK-1, TASK-3, and G236R variant; functional electrophysiology","journal":"Structure","confidence":"High","confidence_rationale":"Tier 1 / Strong — cryo-EM structures of wild-type and disease mutant with functional validation, disease variant mechanism structurally resolved","pmids":["39637865"],"is_preprint":false},{"year":2024,"finding":"TASK-5 (KCNK15) forms functional heterodimers with TASK-3 at the plasma membrane. TASK-5/TASK-3 heteromers show altered single-channel conductance, modified Gq-coupled receptor inhibition, and distinct pharmacological sensitivity compared to TASK-3 homodimers. TASK-5 reduces surface expression of TASK channels when forming heteromers.","method":"Co-expression in heterologous cells, single-channel electrophysiology, pharmacological profiling, surface expression assays","journal":"Nature communications","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — functional heterodimer characterization with biophysical and pharmacological characterization, single lab","pmids":["39215006"],"is_preprint":false}],"current_model":"TASK-3 (KCNK9/K2P9.1) is a two-pore domain background K+ channel that forms homodimers and heterodimers (with TASK-1, TWIK-1, and TASK-5) at the plasma membrane and in mitochondria; extracellular acidification inhibits the channel via His98 protonation triggering a cation-π interaction with Trp78 that drives C-type inactivation of the selectivity filter, as revealed by cryo-EM; voltage-dependent gating at the cytoplasmic mouth (X-gate) provides a second gating mechanism; channel trafficking to the surface requires 14-3-3 binding to a C-terminal phosphoserine (phosphorylated by PKA) that masks a COPI retention signal (KRR), while surface expression also depends on a di-acidic EDE ER-export motif and KCC2 interaction; volatile anesthetics activate the channel through Met159 at the transmembrane/C-terminus interface, the same region required for Gαq/neurotransmitter inhibition; PKCα phosphorylates Thr341 to reduce current while TNFα enhances gating through the ASK1/JNK/p38 pathway; oncogenic functions require intact K+ channel conductance, and mitochondrial TASK-3 regulates mitochondrial membrane potential and aldosterone synthesis in adrenal glomerulosa cells; loss-of-function mutations (especially G236R, which disrupts the X-gate) in the maternally expressed, paternally imprinted KCNK9 allele cause KCNK9 imprinting syndrome (Birk-Barel syndrome)."},"narrative":{"mechanistic_narrative":"KCNK9 (TASK-3/K2P9.1) encodes a two-pore-domain background K+ channel that conducts a time-independent, non-inactivating, pH-sensitive leak current setting resting membrane potential in excitable cells [PMID:10734076, PMID:10747866]. The channel is gated extracellularly by protons: His98 in the outer pore acts as the pH sensor [PMID:10734076, PMID:10747866], and cryo-EM at neutral and acidic pH shows that His98 protonation drives C-type inactivation by engaging a cation-π interaction with Trp78, dilating the selectivity-filter mouth while a hydrophobic gate blocks conduction [PMID:38630723]; a second, lower cytoplasmic 'X-gate' provides voltage-dependent gating at the inner pore [PMID:19703964, PMID:39637865]. TASK-3 functions as a homodimer and assembles heterodimers with TASK-1, TWIK-1, and TASK-5, generating channels with intermediate pH sensitivity, distinct conductance, and altered pharmacology that account for native background currents in motoneurons, cerebellar granule neurons, and carotid body glomus cells [PMID:11733509, PMID:15282272, PMID:30416196, PMID:39215006, PMID:19403596]. Surface delivery is tightly controlled: PKA phosphorylation of a C-terminal serine enables 14-3-3 binding that masks a tri-basic COPI retention signal (KRR), while a di-acidic EDE motif drives COPII-dependent ER export and KCC2 interaction supports membrane expression [PMID:12433946, PMID:19139046, PMID:21357689, PMID:17547699, PMID:31269453]. Channel activity is modulated by an interface region at the transmembrane/C-terminus boundary that mediates both volatile-anesthetic activation (via Met159) and Gαq/neurotransmitter inhibition [PMID:11886861, PMID:22147752, PMID:25405940], and PKCα phosphorylation of Thr341 reduces current [PMID:17374744]. TASK-3 supports oncogenic proliferation and apoptosis resistance in a manner strictly dependent on intact K+ conductance [PMID:12782791], and resides in mitochondria of adrenal zona glomerulosa cells where it controls mitochondrial membrane potential and aldosterone synthesis [PMID:28630209]. Loss-of-function mutations in the maternally expressed, paternally imprinted KCNK9 allele—notably G236R, which disrupts the X-gate—cause KCNK9 imprinting (Birk-Barel) syndrome [PMID:18678320, PMID:39637865].","teleology":[{"year":2000,"claim":"Established that KCNK9 encodes a background K+ channel whose defining property is extracellular pH sensitivity, and pinpointed the molecular sensor.","evidence":"Heterologous expression with patch-clamp and His98 mutagenesis in COS-7, HEK293, and Xenopus oocytes","pmids":["10734076","10747866"],"confidence":"High","gaps":["Structural basis of how His98 protonation closes the pore not yet resolved","Native cellular roles unaddressed"]},{"year":2001,"claim":"Showed TASK-3 is not obligately homodimeric but forms functional heterodimers with TASK-1, expanding the diversity of background currents it can generate.","evidence":"Xenopus oocyte co-expression and tandem-linked constructs with voltage clamp, plus immunofluorescence localization","pmids":["11733509"],"confidence":"High","gaps":["Whether heterodimers form in native tissue not yet shown","Stoichiometry and assembly determinants undefined"]},{"year":2002,"claim":"Mapped the C-terminal/transmembrane interface as the locus for anesthetic activation and neurotransmitter inhibition, and identified a 14-3-3-based trafficking checkpoint controlling surface expression.","evidence":"Site-directed mutagenesis with electrophysiology; yeast two-hybrid, Co-IP, and surface expression assays for 14-3-3","pmids":["11886861","12433946"],"confidence":"High","gaps":["Identity of the retention signal masked by 14-3-3 not yet defined","Kinase generating the 14-3-3 binding site unknown"]},{"year":2002,"claim":"Linked TASK-3 to a physiological tissue role by showing it dominates the adrenal glomerulosa background conductance and is inhibited by angiotensin II receptor signaling.","evidence":"Northern blot, qRT-PCR, oocyte electrophysiology, and pharmacological matching to native current","pmids":["11875121"],"confidence":"Medium","gaps":["Native channel identity inferred pharmacologically, not by genetic ablation","Downstream consequence for aldosterone not yet tested"]},{"year":2003,"claim":"Demonstrated that the oncogenic activity of TASK-3 requires functional K+ conductance, linking channel biophysics directly to tumor biology.","evidence":"Pore mutant (G95E) with dominant-negative validation, proliferation/apoptosis assays, and nude mouse xenograft","pmids":["12782791"],"confidence":"High","gaps":["Signaling pathway connecting K+ flux to proliferation unresolved","Tumor types dependent on TASK-3 not delineated"]},{"year":2003,"claim":"Resolved the molecular site of ruthenium red block, defining Glu70 in the extracellular loop as a bridging site spanning both subunits.","evidence":"Tandem-construct mutagenesis with Hill analysis and gain-of-function transfer to TASK-1","pmids":["12606773"],"confidence":"High","gaps":["Physiological ligand for the Glu70 site not identified at this stage"]},{"year":2004,"claim":"Confirmed TASK-1/TASK-3 heterodimers exist in native neurons and carry physiologically relevant currents, validating heteromerization beyond heterologous systems.","evidence":"Co-IP, dominant-negative suppression, tandem-construct and native motoneuron/granule-neuron patch-clamp with pharmacological profiling","pmids":["15282272","14678492"],"confidence":"High","gaps":["Relative abundance of homo- vs heteromers in each cell type not quantified","Functional consequence of heteromer-specific gating uncharacterized"]},{"year":2006,"claim":"Generalized the Glu70 site as a polycation/divalent sensor and identified an activity-dependent transcriptional control of TASK-3 via Ca2+/calcineurin.","evidence":"Charge-swap mutagenesis with single-channel recording; depolarization paradigm with L-type channel/calcineurin blockade and RT-PCR","pmids":["16513667","16864570"],"confidence":"High","gaps":["Transcription factor downstream of calcineurin not identified","In vivo relevance of activity-dependent regulation untested"]},{"year":2007,"claim":"Defined the ER-export and PKC regulatory mechanisms: a di-acidic EDE motif drives COPII-dependent export, and PKCα phosphorylation of Thr341 limits Gq-mediated inhibition.","evidence":"Surface expression assays, live imaging, Sar1 dominant-negative; phosphosite mutagenesis, PKCα siRNA, and Gαq antagonist with patch-clamp","pmids":["17547699","17374744"],"confidence":"High","gaps":["How EDE/COPII export integrates with downstream 14-3-3 checkpoint not unified","Whether Gαq acts truly directly on the channel debated at the time"]},{"year":2008,"claim":"Established loss-of-function as the disease mechanism for Birk-Barel syndrome and probed pore architecture by disulfide crosslinking the M1P1 loop to the pore.","evidence":"Electrophysiology of the G236R disease variant in homo/heterodimers; cysteine-substitution disulfide trapping between Glu70 and His98","pmids":["18678320","18417474"],"confidence":"High","gaps":["Imprinting basis of maternal-allele effect not addressed here","Structural gating change caused by G236R not yet visualized"]},{"year":2009,"claim":"Defined dual gating (selectivity filter plus cytoplasmic gate) and refined the 14-3-3 trafficking model by identifying the masked COPI retention signal.","evidence":"Single-channel kinetic modeling with M2/M4/hinge mutagenesis; GST pulldown of COPI with the KRR motif and GFP localization in multiple systems; native carotid body single-channel comparison","pmids":["19703964","19139046","19403596"],"confidence":"Medium","gaps":["Atomic structure of the cytoplasmic gate not yet available","Coupling between filter and cytoplasmic gates inferred from kinetics only"]},{"year":2011,"claim":"Connected the trafficking checkpoint to a defined kinase and resolved the anesthetic activation residue, showing PKA-phosphorylated Ser373 enables 14-3-3-mediated export and Met159 forms the anesthetic site.","evidence":"In vitro kinase assay with surface GFP assay; M159C NEM modification with tandem dimers and electrophysiology","pmids":["21357689","22147752"],"confidence":"Medium","gaps":["In vivo kinase regulation of trafficking not tested","Anesthetic binding pocket not structurally resolved at this point"]},{"year":2013,"claim":"Localized TASK-3 to mitochondria of aldosterone-producing cells and tied it functionally to steroidogenesis, while refining the disease mutant as hypomorphic rather than null.","evidence":"Yeast two-hybrid, immunoprecipitation, EM, and TASK-3 knockout mouse mitochondrial/aldosterone phenotyping; electrophysiology of G236R with pharmacological rescue","pmids":["28630209","24342771"],"confidence":"High","gaps":["Mechanism by which a K+ channel sets mitochondrial membrane potential unclear","How residual G236R current relates to clinical severity unresolved"]},{"year":2014,"claim":"Defined in vivo neuronal roles: TASK-3 sets cold-sensing thresholds in TRPM8 neurons and is the target of neurotensin-NTS1/Gαq signaling in dentate gyrus granule cells.","evidence":"TASK-3 knockout behavioral assays with FACS profiling of TRPM8 neurons; brain-slice patch-clamp with Co-IP showing NTS1-induced Gαq/TASK-3 association","pmids":["25199828","25405940"],"confidence":"High","gaps":["Whether Gαq contacts the channel directly versus through an adaptor not fully settled","Contribution of heteromers to these phenotypes not dissected"]},{"year":2015,"claim":"Localized the binding site of breathing-stimulant inhibitors to the intracellular pore, identifying L122 and G236 as drug-contact residues.","evidence":"Homology modeling, docking, and mutagenesis with Ussing chamber electrophysiology for PKTHPP, A1899, and doxapram","pmids":["26268529"],"confidence":"Medium","gaps":["Site inferred from modeling/mutagenesis without a co-structure","Selectivity over TASK-1 not addressed"]},{"year":2018,"claim":"Identified TWIK-1 as a further heterodimeric partner of TASK-3 shaping dentate gyrus granule cell excitability.","evidence":"Co-IP from hippocampus and COS-7 cells, shRNA knockdown, and patch-clamp of granule cells","pmids":["30416196"],"confidence":"Medium","gaps":["Stoichiometry and gating of TWIK-1/TASK-3 heteromer not fully defined","Single-lab Co-IP without structural confirmation"]},{"year":2019,"claim":"Added KCC2 as a trafficking partner required for TASK-3 surface expression and characterized species- and pore-dependent doxapram pharmacology.","evidence":"Co-IP, KCC2 shRNA, fractionation, chemogenetic rescue, and patch-clamp; enantiomer and pore-residue mutagenesis with human/mouse comparison","pmids":["31269453","31423744"],"confidence":"Medium","gaps":["Whether KCC2 acts via direct interaction or chaperone effect not fully resolved","Structural basis of doxapram species selectivity unknown"]},{"year":2020,"claim":"Showed that the natural compound withaferin A inhibits TASK-3 at defined pore residues and that its cytotoxicity in cancer cells is TASK-3-dependent, reinforcing the oncogenic relevance of the channel.","evidence":"Patch-clamp, docking, F125/L197 mutagenesis, and TASK-3 overexpression/knockdown viability assays in MDA-MB-231 cells","pmids":["32563149"],"confidence":"Medium","gaps":["Binding pose inferred from docking, not co-structure","In vivo antitumor efficacy untested"]},{"year":2022,"claim":"Broadened the disease genotype-phenotype map, showing KCNK9 imprinting syndrome arises from both gain and loss of conductance with altered regulatory control as the common theme.","evidence":"Electrophysiology of 15 variants with 3D molecular dynamics modeling and clinical/facial phenotyping","pmids":["35698242"],"confidence":"Medium","gaps":["Structural validation relied on modeling rather than experimental structures","Mechanistic link between altered regulation and phenotype not established"]},{"year":2024,"claim":"Provided the structural mechanism of pH gating and disease, resolving cryo-EM structures that show His98-Trp78 cation-π-driven C-type inactivation and an X-gate disrupted by the G236R variant.","evidence":"Cryo-EM of TASK-3 at two pH states and of TASK-1/TASK-3 G236R, with MD simulations, mutagenesis, and electrophysiology; plus TASK-5/TASK-3 heterodimer characterization","pmids":["38630723","39637865","39215006"],"confidence":"High","gaps":["Structures of regulatory complexes (14-3-3, KCC2, Gαq) with the channel not yet determined","Mitochondrial channel structure/function relationship unresolved"]},{"year":null,"claim":"How the many regulatory inputs (PKA/14-3-3 trafficking, PKCα, Gαq, KCC2, heteromerization) are integrated at the channel in vivo, and how K+ conductance is mechanistically coupled to oncogenesis and mitochondrial/aldosterone control, remains unresolved.","evidence":"","pmids":[],"confidence":"Medium","gaps":["No structure of TASK-3 bound to a trafficking or signaling partner","Causal link between channel flux and proliferation undefined","Mechanism by which a plasma-membrane-type K+ channel operates in mitochondria unknown"]}],"mechanism_profile":{"molecular_activity":[{"term_id":"GO:0005215","term_label":"transporter activity","supporting_discovery_ids":[0,1,6,18,32]},{"term_id":"GO:0140299","term_label":"molecular sensor activity","supporting_discovery_ids":[0,1,32]}],"localization":[{"term_id":"GO:0005886","term_label":"plasma membrane","supporting_discovery_ids":[2,4,12,16,34]},{"term_id":"GO:0005739","term_label":"mitochondrion","supporting_discovery_ids":[23]},{"term_id":"GO:0005783","term_label":"endoplasmic reticulum","supporting_discovery_ids":[12,16,19]},{"term_id":"GO:0005794","term_label":"Golgi apparatus","supporting_discovery_ids":[16]}],"pathway":[{"term_id":"R-HSA-112316","term_label":"Neuronal System","supporting_discovery_ids":[8,24,25,27]},{"term_id":"R-HSA-9609507","term_label":"Protein localization","supporting_discovery_ids":[4,12,16,19,28]},{"term_id":"R-HSA-162582","term_label":"Signal Transduction","supporting_discovery_ids":[13,25]},{"term_id":"R-HSA-1643685","term_label":"Disease","supporting_discovery_ids":[14,22,31]}],"complexes":["TASK-1/TASK-3 heterodimer","TWIK-1/TASK-3 heterodimer","TASK-5/TASK-3 heterodimer"],"partners":["KCNK3","KCNK1","KCNK15","YWHAZ","SLC12A5","GNAQ","PRKCA","COPB1"],"other_free_text":[]}},"prefetch_data":{"uniprot":{"accession":"Q9NPC2","full_name":"Potassium channel subfamily K member 9","aliases":["Acid-sensitive potassium channel protein TASK-3","TWIK-related acid-sensitive K(+) channel 3","Two pore potassium channel KT3.2","Two pore K(+) channel KT3.2"],"length_aa":374,"mass_kda":42.3,"function":"K(+) channel that conducts voltage-dependent outward rectifying currents upon membrane depolarization. Voltage sensing is coupled to K(+) electrochemical gradient in an 'ion flux gating' mode where outward but not inward ion flow opens the gate (PubMed:11042359, PubMed:11431495, PubMed:26919430, PubMed:38630723). Changes ion selectivity and becomes permeable to Na(+) ions in response to extracellular acidification. Protonation of the pH sensor His-98 stabilizes C-type inactivation conformation likely converting the channel from outward K(+)-conducting, to inward Na(+)-conducting to nonconductive state (PubMed:22948150, PubMed:38630723). Homo- and heterodimerizes to form functional channels with distinct regulatory and gating properties (By similarity) (PubMed:23169818, PubMed:38630723). Allows K(+) currents with fast-gating kinetics important for the repolarization and hyperpolarization phases of action potentials (By similarity). In granule neurons, hyperpolarizes the resting membrane potential to limit intrinsic neuronal excitability, but once the action potential threshold is reached, supports high-frequency action potential firing and increased neuronal excitability. Homomeric and/or heteromeric KCNK3:KCNK9 channels operate in cerebellar granule cells, whereas heteromeric KCNK1:KCNK9 enables currents in hippocampal dentate gyrus granule neurons (By similarity). Dispensable for central chemosensory respiration i.e. breathing controlled by brainstem CO2/pH, it rather conducts pH-sensitive currents and controls the firing rate of serotonergic raphe neurons involved in potentiation of the respiratory chemoreflex (By similarity). In retinal ganglion cells, mediates outward currents that regulate action potentials in response to acidification of the synaptic cleft. Involved in transmission of image-forming and nonimage-forming visual information in the retina (By similarity). In adrenal gland, contributes to the maintenance of a hyperpolarized resting membrane potential of aldosterone-producing cells at zona glomerulosa and limits aldosterone release as part of a regulatory mechanism that controls arterial blood pressure and electrolyte homeostasis (By similarity)","subcellular_location":"Cell membrane; Mitochondrion inner membrane; Cell projection, dendrite","url":"https://www.uniprot.org/uniprotkb/Q9NPC2/entry"},"depmap":{"release":"DepMap","has_data":true,"is_common_essential":false,"resolved_as":"","url":"https://depmap.org/portal/gene/KCNK9","classification":"Not Classified","n_dependent_lines":2,"n_total_lines":1208,"dependency_fraction":0.0016556291390728477},"opencell":{"profiled":false,"resolved_as":"","ensg_id":"","cell_line_id":"","localizations":[],"interactors":[],"url":"https://opencell.sf.czbiohub.org/search/KCNK9","total_profiled":1310},"omim":[{"mim_id":"613677","title":"HYPERALDOSTERONISM, FAMILIAL, TYPE III; HALD3","url":"https://www.omim.org/entry/613677"},{"mim_id":"612292","title":"BIRK-BAREL SYNDROME; BIBARS","url":"https://www.omim.org/entry/612292"},{"mim_id":"610873","title":"MENARCHE, AGE AT, QUANTITATIVE TRAIT LOCUS 1; MENAQ1","url":"https://www.omim.org/entry/610873"},{"mim_id":"607368","title":"POTASSIUM CHANNEL, SUBFAMILY K, MEMBER 15; KCNK15","url":"https://www.omim.org/entry/607368"},{"mim_id":"605874","title":"POTASSIUM CHANNEL, SUBFAMILY K, MEMBER 9; KCNK9","url":"https://www.omim.org/entry/605874"}],"hpa":{"profiled":true,"resolved_as":"","reliability":"Approved","locations":[{"location":"Plasma membrane","reliability":"Approved"}],"tissue_specificity":"Tissue enriched","tissue_distribution":"Detected in some","driving_tissues":[{"tissue":"brain","ntpm":7.4}],"url":"https://www.proteinatlas.org/search/KCNK9"},"hgnc":{"alias_symbol":["K2p9.1","TASK3","TASK-3"],"prev_symbol":[]},"alphafold":{"accession":"Q9NPC2","domains":[{"cath_id":"1.10.287.70","chopping":"75-262","consensus_level":"high","plddt":92.2134,"start":75,"end":262},{"cath_id":"1.10.287","chopping":"1-54","consensus_level":"medium","plddt":94.2876,"start":1,"end":54}],"viewer_url":"https://alphafold.ebi.ac.uk/entry/Q9NPC2","model_url":"https://alphafold.ebi.ac.uk/files/AF-Q9NPC2-F1-model_v6.cif","pae_url":"https://alphafold.ebi.ac.uk/files/AF-Q9NPC2-F1-predicted_aligned_error_v6.png","plddt_mean":75.94},"mouse_models":{"mgi_url":"https://www.informatics.jax.org/marker/summary?nomen=KCNK9","jax_strain_url":"https://www.jax.org/strain/search?query=KCNK9"},"sequence":{"accession":"Q9NPC2","fasta_url":"https://rest.uniprot.org/uniprotkb/Q9NPC2.fasta","uniprot_url":"https://www.uniprot.org/uniprotkb/Q9NPC2/entry","alphafold_viewer_url":"https://alphafold.ebi.ac.uk/entry/Q9NPC2"}},"corpus_meta":[{"pmid":"10734076","id":"PMC_10734076","title":"TASK-3, a new member of the tandem pore K(+) channel family.","date":"2000","source":"The Journal of biological chemistry","url":"https://pubmed.ncbi.nlm.nih.gov/10734076","citation_count":313,"is_preprint":false},{"pmid":"10747866","id":"PMC_10747866","title":"TASK-3, a novel tandem pore domain acid-sensitive K+ channel. 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time-independent, non-inactivating K+-selective background current. Mutation of histidine at position 98 to aspartate abolished extracellular pH sensitivity, identifying His98 as the critical pH sensor.\",\n      \"method\": \"Heterologous expression in COS-7 cells, whole-cell and single-channel patch-clamp, site-directed mutagenesis\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — reconstitution in heterologous cells with mutagenesis, independently replicated in a second paper the same year (PMID:10747866)\",\n      \"pmids\": [\"10734076\", \"10747866\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2000,\n      \"finding\": \"His98, located at the outer pore adjacent to the selectivity filter, is an essential component of the extracellular pH sensor; substitution of His98 with asparagine or tyrosine abolished pH sensitivity. Single-channel recordings in HEK293 cells showed inwardly rectifying I-V relationship with open probability increasing markedly with depolarization.\",\n      \"method\": \"Xenopus oocyte expression, HEK293 cell-attached patch-clamp, site-directed mutagenesis\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — in vitro reconstitution with mutagenesis, replicated across two independent labs (PMID:10734076 and PMID:10747866)\",\n      \"pmids\": [\"10747866\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2001,\n      \"finding\": \"TASK-1 and TASK-3 form functional heterodimers when co-expressed in Xenopus oocytes. A tandem-linked TASK-3/TASK-1 construct yielded currents with intermediate pH sensitivity and ruthenium red insensitivity (TASK-1-like). Epitope-tagged channels localized primarily to the plasma membrane in mammalian cells.\",\n      \"method\": \"Xenopus oocyte co-expression, tandem-linked constructs, two-electrode voltage clamp, immunofluorescence localization in mammalian cells\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 / Strong — functional heterodimer reconstitution in two systems, tandem construct validation, replicated by multiple subsequent labs\",\n      \"pmids\": [\"11733509\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2002,\n      \"finding\": \"A six-residue sequence at the beginning of the cytoplasmic C-terminus (interface of final transmembrane domain and C-terminus) is required for both volatile anesthetic (halothane) activation and neurotransmitter (TRH) inhibition of TASK-3; mutations in this region virtually abolished both effects. The identified phosphorylation site within this region was not required for modulation.\",\n      \"method\": \"Site-directed mutagenesis, heterologous expression, whole-cell electrophysiology\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — reconstitution with systematic mutagenesis, multiple mutants tested with two distinct modulators, single lab\",\n      \"pmids\": [\"11886861\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2002,\n      \"finding\": \"TASK-3 C-terminal domain interacts with 14-3-3 adapter proteins via a C-terminal RRx(S/T)x motif. This interaction promotes surface membrane expression; deletion of a single C-terminal amino acid abolished 14-3-3 binding and strongly reduced macroscopic currents. Co-injection of 14-3-3ζ increased TASK-3 current by ~70% in oocytes. TASK-1 and 14-3-3 co-immunoprecipitated from synaptic membranes.\",\n      \"method\": \"Yeast two-hybrid, co-immunoprecipitation, Xenopus oocyte voltage clamp, GFP surface expression assay in HEK293 cells, truncation/point mutagenesis\",\n      \"journal\": \"The Journal of physiology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 / Strong — multiple orthogonal methods (Y2H, Co-IP, electrophysiology, surface expression), independently confirmed in subsequent trafficking studies\",\n      \"pmids\": [\"12433946\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2002,\n      \"finding\": \"TASK-3 dominates the background K+ conductance of rat adrenal glomerulosa cells. The pharmacological profile of native glomerulosa current (ruthenium red sensitivity in micromolar range, weak acid sensitivity) matches TASK-3, and TASK-3 current is inhibited by AT1a angiotensin II receptor stimulation when co-expressed.\",\n      \"method\": \"Northern blot, quantitative RT-PCR, Xenopus oocyte electrophysiology, pharmacological characterization\",\n      \"journal\": \"Molecular endocrinology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2-3 / Moderate — pharmacological matching of native current to cloned channel, functional angiotensin II inhibition in reconstituted system, single lab\",\n      \"pmids\": [\"11875121\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2003,\n      \"finding\": \"Oncogenic functions of TASK3 (KCNK9) — promoting proliferation in low serum, resistance to apoptosis, and tumor growth in nude mice — require intact K+ channel function. A pore mutation (G95E) abolished both K+ current and oncogenic activity. G95E acts as a dominant-negative, suppressing wild-type TASK3 current and tumorigenicity when co-expressed.\",\n      \"method\": \"Site-directed mutagenesis, patch-clamp electrophysiology, cell proliferation assays, apoptosis assays, nude mouse xenograft\",\n      \"journal\": \"Proceedings of the National Academy of Sciences of the United States of America\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 / Strong — mutagenesis directly links channel activity to oncogenic function, dominant-negative validation, in vivo xenograft, multiple orthogonal assays\",\n      \"pmids\": [\"12782791\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2003,\n      \"finding\": \"Ruthenium red inhibits TASK-3 by simultaneously binding glutamate 70 (Glu70) on both subunits of the dimer. Mutation of Glu70 to Arg or Cys in either subunit of a tandem construct abolished RR inhibition. The Hill coefficient of ~1.0 indicates one RR molecule bridges both subunits. Introducing Glu at position 70 of TASK-1 (K70E) conferred RR sensitivity.\",\n      \"method\": \"Site-directed mutagenesis of tandem constructs, Xenopus oocyte electrophysiology, pharmacological dose-response analysis\",\n      \"journal\": \"Molecular pharmacology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — systematic mutagenesis of both subunits in tandem constructs with gain-of-function in TASK-1, mechanistically rigorous\",\n      \"pmids\": [\"12606773\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2004,\n      \"finding\": \"TASK-1/TASK-3 heterodimers are expressed in native hypoglossal motoneurons. Co-immunoprecipitation from transfected mammalian cell membranes confirmed physical association. A dominant-negative TASK-1(Y191F) suppressed TASK-3 currents. Heteromeric channels display intermediate pH sensitivity (pK ~7.3) and are activated (not inhibited) by high isoflurane, matching native motoneuron TASK currents.\",\n      \"method\": \"Co-immunoprecipitation, dominant-negative suppression, tandem-linked heterodimer electrophysiology, native neuron patch-clamp, pharmacological profiling\",\n      \"journal\": \"The Journal of neuroscience\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — reciprocal Co-IP, dominant-negative, tandem construct, native cell validation, multiple orthogonal methods\",\n      \"pmids\": [\"15282272\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2004,\n      \"finding\": \"Native 38-pS K+ channels in cerebellar granule neurons include both homomeric TASK-3 and heteromeric TASK-1/TASK-3 channels, identified by differential sensitivity to ruthenium red and extracellular pH changes matching cloned homomers and heterodimers.\",\n      \"method\": \"Single-channel patch-clamp of cultured cerebellar granule neurons and COS-7-expressed cloned channels, pharmacological profiling with ruthenium red and pH\",\n      \"journal\": \"The Journal of physiology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — direct single-channel comparison between native and cloned channels, single lab, pharmacological but not molecular validation in native tissue\",\n      \"pmids\": [\"14678492\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2006,\n      \"finding\": \"Glutamate 70 (Glu70) in the extracellular loop of TASK-3 mediates sensitivity to divalent cations (Ca2+, Mg2+) and polycations (spermine, ruthenium red). Replacing Glu70 with Lys or Arg abolished divalent cation sensitivity; the reverse mutation in TASK-1 (K70E) induced this sensitivity. Spermine and ruthenium red also decrease open probability likely by binding Glu70.\",\n      \"method\": \"Site-directed mutagenesis, HEK293 cell single-channel and whole-cell electrophysiology, charge-swap experiments\",\n      \"journal\": \"The Journal of physiology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — systematic mutagenesis with gain-of-function in TASK-1 and loss-of-function in TASK-3, multiple orthogonal pharmacological agents\",\n      \"pmids\": [\"16513667\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2006,\n      \"finding\": \"Transcription of TASK-3 in cerebellar granule neurons is regulated by membrane depolarization through Ca2+ entry via L-type channels and the downstream effector calcineurin. Blocking L-type Ca2+ channels or calcineurin abrogated TASK-3 mRNA and protein upregulation and the IKso conductance, causing hyperexcitability.\",\n      \"method\": \"In vitro neuronal culture in depolarizing/non-depolarizing KCl conditions, pharmacological blockade of L-type channels and calcineurin, RT-PCR, patch-clamp\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — pharmacological epistasis identifying calcineurin pathway, functional current measurements, single lab\",\n      \"pmids\": [\"16864570\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2007,\n      \"finding\": \"Di-acidic motif EDE in the proximal C-terminus of TASK-3 is required for efficient ER export and surface membrane expression. Mutation of the two glutamate residues (ADA mutant) markedly reduced surface expression and retained the channel in the ER. ER export of TASK-3 requires COPII machinery (blocked by dominant-negative Sar1H79G).\",\n      \"method\": \"Luminometric surface expression assay, Xenopus oocyte voltage clamp, live-cell GFP imaging in COS-7 cells, Sar1 dominant-negative co-expression, chimeric constructs\",\n      \"journal\": \"Traffic\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — multiple orthogonal methods (surface assay, electrophysiology, live imaging, dominant-negative), mechanistically rigorous ER export pathway\",\n      \"pmids\": [\"17547699\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2007,\n      \"finding\": \"Protein kinase C (PKCα) phosphorylates Thr341 in the C-terminus of human TASK3, thereby reducing channel current. Gαq-coupled M3 muscarinic receptor inhibition of TASK3 occurs through a direct action of Gαq on the channel (not through PKC), while PKC activation opposes and limits the duration of Gq-mediated inhibition.\",\n      \"method\": \"Site-directed mutagenesis of phosphorylation site, siRNA knockdown of PKCα, selective PKC inhibitors, Gαq antagonist (YM-254890), whole-cell patch-clamp\",\n      \"journal\": \"Molecular pharmacology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 / Strong — mutagenesis of phosphorylation site, gene silencing, selective antagonist, multiple orthogonal approaches in single lab\",\n      \"pmids\": [\"17374744\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2008,\n      \"finding\": \"The Birk Barel syndrome missense mutation G236R in the maternal copy of KCNK9 fully abolishes channel currents both when functioning as a homodimer and as a heterodimer with K2P3.1 (TASK-1), establishing loss-of-function as the disease mechanism.\",\n      \"method\": \"Electrophysiological characterization of mutant channels in heterologous expression system, genetic mapping\",\n      \"journal\": \"American journal of human genetics\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 / Strong — direct electrophysiological demonstration of loss-of-function in both homo- and heterodimeric configurations, disease-causing variant\",\n      \"pmids\": [\"18678320\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2008,\n      \"finding\": \"The M1P1 extracellular loop of TASK-3 lies close to the pore and regulates channel activity. Disulfide bond formation between Cys substitutions at Glu70 (M1P1 loop) and His98 (pore) in tandem constructs confirms their spatial proximity. The M1P1 loop also participates in pH regulation of TASK-3.\",\n      \"method\": \"Site-directed mutagenesis with cysteine substitutions, tandem-fixed constructs, dithiothreitol/cadmium probing, loop-swap chimeras, patch-clamp\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — disulfide crosslinking between engineered cysteines, gain-of-function with cadmium, chimera experiments, single lab\",\n      \"pmids\": [\"18417474\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2009,\n      \"finding\": \"TASK-3 surface expression is controlled by 14-3-3 binding masking a tri-basic COPI retention signal (KRR) in the C-terminus. When 14-3-3 binding is disabled, KRR is exposed and binds COPI coatomer, retaining the channel in the Golgi. TASK-3 also has an independent di-basic N-terminal retention signal (KR). 14-3-3 binding does not affect dimeric assembly.\",\n      \"method\": \"Mutational analysis in Xenopus oocytes, mammalian cells and yeast; GST pulldown of COPI with KRR motif; GFP-tagged channel localization; dominant-negative suppression of dimerization\",\n      \"journal\": \"The Journal of physiology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 / Strong — GST pulldown identifies COPI binding, mutagenesis in multiple systems, subcellular localization directly linked to trafficking mechanism\",\n      \"pmids\": [\"19139046\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2009,\n      \"finding\": \"TASK-1/TASK-3 heteromers are the major oxygen-sensitive background K+ channels in rat carotid body glomus cells, contributing ~75% of TASK-like current. Discrimination among TASK-1, TASK-3, and TASK-1/3 heteromers was achieved by comparing single-channel conductances in defined Mg2+ conditions and ruthenium red sensitivity in native cells vs. cloned channels.\",\n      \"method\": \"Single-channel patch-clamp of native carotid body cells and cloned channels in outside-out/cell-attached configuration, pharmacological profiling with ruthenium red and methanandamide\",\n      \"journal\": \"The Journal of physiology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — rigorous biophysical comparison of native vs. cloned channel properties, pharmacological orthogonal probes, single lab\",\n      \"pmids\": [\"19403596\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2009,\n      \"finding\": \"TASK-3 voltage-dependent gating involves a cytoplasmic gate in addition to the selectivity filter. Mutations in M2 (N133A) and M4 (A237T) increase open probability and shift voltage dependence, while mutating conserved hinge glycines (G117A, G231A) decreases open probability. Two routes out of the open state indicate dual gating at selectivity filter and cytoplasmic mouth.\",\n      \"method\": \"Two-electrode voltage clamp, single-channel recording, kinetic modeling, site-directed mutagenesis\",\n      \"journal\": \"The Journal of physiology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — systematic mutagenesis with single-channel analysis and kinetic modeling, single lab\",\n      \"pmids\": [\"19703964\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2011,\n      \"finding\": \"Protein kinase A (PKA/cAMP-dependent protein kinase) phosphorylates Ser373 in the C-terminus of TASK-3 (K2P9.1), and this phosphorylation enables 14-3-3 binding to overcome ER retention by βCOP, thus promoting forward trafficking to the plasma membrane.\",\n      \"method\": \"In vitro phosphorylation assays, bioinformatics candidate selection, electrophysiology in HEK293 cells, cell surface GFP assay\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 1-2 / Moderate — in vitro kinase assay plus functional surface expression assay, single lab, identifies specific phosphorylation site\",\n      \"pmids\": [\"21357689\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2011,\n      \"finding\": \"Met159 in TASK-3 is essential for volatile anesthetic activation and contributes to the anesthetic binding site. Covalent modification of M159C by NEM irreversibly activated the channel and rendered it resistant to inhibition by both acidic pH and active Gαq protein. A single modified subunit in a wild-type/M159C tandem is sufficient for activation, indicating cross-talk between subunits.\",\n      \"method\": \"Site-directed mutagenesis (M159C, M159W, M159F), cysteine-reactive NEM modification, tandem dimers, electrophysiology in Fischer rat thyroid cells (Ussing chamber)\",\n      \"journal\": \"Molecular pharmacology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — covalent modification strategy with mutagenesis and tandem constructs, mechanistically rigorous, identifies specific residue\",\n      \"pmids\": [\"22147752\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2012,\n      \"finding\": \"N-linked glycosylation of TASK-3 (K2P9.1) occurs at the conserved consensus site; however, disruption of glycosylation causes only a small reduction in cell surface channels with no detectable functional change in K+ current, in contrast to TASK-1 where glycosylation loss significantly reduces surface expression and current.\",\n      \"method\": \"Flow cytometry surface expression assay, patch-clamp, site-directed mutagenesis of glycosylation site, tunicamycin treatment\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — multiple orthogonal methods, clear functional contrast with TASK-1, single lab\",\n      \"pmids\": [\"23250752\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2013,\n      \"finding\": \"The Birk Barel G236R mutant TASK-3 produces a small, inwardly rectifying current (not zero current) with altered responses to extracellular acidification, zinc, and Gαq-coupled muscarinic receptors compared to wild-type. A gain-of-function second mutation A237T and the NSAID flufenamic acid partially restore outward current through G236R channels.\",\n      \"method\": \"Whole-cell electrophysiology of wild-type and G236R mutant TASK-3, pharmacological profiling, double mutants\",\n      \"journal\": \"Molecular pharmacology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 1-2 / Moderate — electrophysiological characterization of disease mutant with pharmacological rescue, single lab\",\n      \"pmids\": [\"24342771\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2013,\n      \"finding\": \"TASK-3 channels are present in mitochondria of aldosterone-producing zona glomerulosa cells, confirmed by yeast two-hybrid, immunoprecipitation, and electron microscopy. Genetic deletion of TASK-3 from mice disrupts mitochondrial morphology, mitochondrial membrane potential, and aldosterone production without changing plasma membrane potential of glomerulosa cells.\",\n      \"method\": \"Yeast two-hybrid, immunoprecipitation, electron microscopy, mitochondrial membrane potential measurements, aldosterone assays in TASK-3 knockout mice\",\n      \"journal\": \"Hypertension\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 / Strong — three orthogonal methods confirming mitochondrial localization, functional KO phenotype, mechanistically links mitochondrial TASK-3 to aldosterone regulation\",\n      \"pmids\": [\"28630209\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2014,\n      \"finding\": \"TASK-3 channels are highly enriched in a subpopulation of TRPM8-positive cold-sensitive neurons. Blockade or genetic knockout of TASK-3 reduces the thermal threshold of cold neurons and causes hypersensitivity to cold in mice, establishing TASK-3 as a modulator of thermosensation in peripheral cold receptors.\",\n      \"method\": \"BAC transgenesis, FACS purification of TRPM8 neurons, molecular profiling, pharmacological blockade, TASK-3 knockout mouse behavioral assays\",\n      \"journal\": \"Cell reports\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — genetic KO with specific behavioral phenotype validated with pharmacological blockade, molecular enrichment analysis\",\n      \"pmids\": [\"25199828\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2014,\n      \"finding\": \"Neurotensin (NT) excites dentate gyrus granule cells via NTS1 receptor-mediated inhibition of TASK-3 K+ channels through direct coupling of Gαq/11 to TASK-3 (not via PLC, IP3-Ca2+, or PKC). Co-immunoprecipitation showed NTS1 activation induced physical association of Gαq/11 with TASK-3.\",\n      \"method\": \"Whole-cell patch-clamp in brain slices, pharmacological dissection, co-immunoprecipitation, receptor-specific antagonists\",\n      \"journal\": \"Cerebral cortex\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — Co-IP demonstrating direct Gαq/TASK-3 association, combined with pharmacological pathway dissection, single lab\",\n      \"pmids\": [\"25405940\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2015,\n      \"finding\": \"Breathing stimulants PKTHPP, A1899, and doxapram inhibit TASK-3 by binding within the intracellular pore region. Mutagenesis identified residues L122 and G236 as critical for drug binding; L122D and G236D mutations increased IC50 >1000-fold. These same mutations conferred resistance to all three compounds.\",\n      \"method\": \"Homology modeling, molecular docking, site-directed mutagenesis, Ussing chamber electrophysiology in Fischer rat thyroid monolayers\",\n      \"journal\": \"Molecular pharmacology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — mutagenesis with functional readout, supported by molecular docking, single lab, three distinct compounds converging on same site\",\n      \"pmids\": [\"26268529\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2018,\n      \"finding\": \"TWIK-1 physically associates with TASK-3 in dentate gyrus granule cells (DGGCs) and in COS-7 cells. TWIK-1/TASK-3 heterodimeric channels display outwardly rectifying currents and contribute to intrinsic excitability of DGGCs. Neurotensin-NTS1 signaling depolarizes DGGCs by inhibiting TWIK-1/TASK-3 heterodimeric channels.\",\n      \"method\": \"Co-immunoprecipitation from mouse hippocampus and COS-7 cells, shRNA knockdown of each subunit, patch-clamp of DGGCs\",\n      \"journal\": \"Experimental & molecular medicine\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — Co-IP from native tissue, shRNA-mediated functional dissection, single lab\",\n      \"pmids\": [\"30416196\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2019,\n      \"finding\": \"KCC2 interacts with TASK-3 (KCNK9) channels and is required for their membrane expression. KCC2 knockdown in rat dentate gyrus neurons reduces TASK-3 surface expression, decreases leak K+ currents, and depolarizes resting membrane potential, leading to increased neuronal excitability and altered network rhythmogenesis.\",\n      \"method\": \"Co-immunoprecipitation of KCC2 and TASK-3, shRNA knockdown of KCC2, patch-clamp, subcellular fractionation, chemogenetic rescue\",\n      \"journal\": \"Cell reports\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — Co-IP demonstrates interaction, KD shows functional consequence on TASK-3 surface expression and excitability, chemogenetic rescue validates specificity\",\n      \"pmids\": [\"31269453\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2019,\n      \"finding\": \"Doxapram inhibits human TASK-3 (hKCNK9) and TASK-1 channels with equal potency (unlike mouse channels where it is TASK-1-selective). Inhibition is attenuated by C-terminus truncation or mutations of hydrophobic pore-lining residues, while an extracellular zinc binding site is not affected. The (+)-enantiomer GAL-054 is more potent than doxapram; the (−)-enantiomer GAL-053 has little effect.\",\n      \"method\": \"Whole-cell patch-clamp in tsA201 cells, site-directed mutagenesis of pore residues, chirally separated enantiomers, species comparison (human vs. mouse)\",\n      \"journal\": \"Acta physiologica\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 1-2 / Moderate — mutagenesis identifies pore residues for inhibition, enantiomer structure-activity analysis, single lab\",\n      \"pmids\": [\"31423744\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2020,\n      \"finding\": \"Withaferin A (WFA) inhibits TASK-3 channels in a dose-dependent, voltage-independent manner. Molecular docking and mutagenesis identified F125 and L197 as critical residues for WFA binding; F125A, L197V, and double mutant markedly reduced WFA inhibition. The cytotoxic effect of WFA in MDA-MB-231 cells depends on TASK-3 expression.\",\n      \"method\": \"Patch-clamp in HEK-293 cells, molecular docking, site-directed mutagenesis, TASK-3 overexpression and shRNA knockdown in cancer cells, cell viability assays\",\n      \"journal\": \"Biomedicine & pharmacotherapy\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 1-2 / Moderate — mutagenesis identifies binding residues, combined with functional cancer cell assays, single lab\",\n      \"pmids\": [\"32563149\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2022,\n      \"finding\": \"KCNK9 imprinting syndrome variants cause both gain and loss of TASK-3 channel conductance, but the most consistent functional impact is altered channel regulation (loss of regulatory control). An additional mutational hotspot was identified at p.Arg131. 3D protein modeling and in vitro electrophysiology define the structural basis of variant effects.\",\n      \"method\": \"In vitro electrophysiology of 15 novel KCNK9 variants, computational 3D molecular mechanics and dynamics, clinical genetics, facial phenotyping\",\n      \"journal\": \"Genome medicine\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 1-2 / Moderate — multiple variants characterized electrophysiologically with structural modeling, but no single orthogonal structural method validated\",\n      \"pmids\": [\"35698242\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2024,\n      \"finding\": \"Cryo-EM structures of human TASK-3 at neutral and acidic pH revealed that extracellular acidification drives C-type inactivation through selectivity filter rearrangement: the SF mouth dilates while a hydrophobic gate blocks the pore. His98 protonation shifts the equilibrium toward the inactivated state by engaging a cation-π interaction with Trp78, as confirmed by MD simulations and mutagenesis.\",\n      \"method\": \"Cryo-EM structural determination at two pH values, molecular dynamics simulations, site-directed mutagenesis of His98 and Trp78, electrophysiology\",\n      \"journal\": \"Proceedings of the National Academy of Sciences of the United States of America\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — high-resolution cryo-EM structures at two pH states, supported by MD simulations and mutagenesis validating mechanistic model\",\n      \"pmids\": [\"38630723\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2024,\n      \"finding\": \"Cryo-EM structures of human TASK-1 and TASK-3 (including the G236R KIS variant) reveal a conserved lower X-gate gating mechanism. The G236R substitution disrupts the X-gate, providing structural explanation for loss-of-function in KCNK9 imprinting syndrome. Combined functional studies confirmed X-gate conformational changes underlie pH-dependent inhibition.\",\n      \"method\": \"Cryo-EM structure determination of wild-type TASK-1, TASK-3, and G236R variant; functional electrophysiology\",\n      \"journal\": \"Structure\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — cryo-EM structures of wild-type and disease mutant with functional validation, disease variant mechanism structurally resolved\",\n      \"pmids\": [\"39637865\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2024,\n      \"finding\": \"TASK-5 (KCNK15) forms functional heterodimers with TASK-3 at the plasma membrane. TASK-5/TASK-3 heteromers show altered single-channel conductance, modified Gq-coupled receptor inhibition, and distinct pharmacological sensitivity compared to TASK-3 homodimers. TASK-5 reduces surface expression of TASK channels when forming heteromers.\",\n      \"method\": \"Co-expression in heterologous cells, single-channel electrophysiology, pharmacological profiling, surface expression assays\",\n      \"journal\": \"Nature communications\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — functional heterodimer characterization with biophysical and pharmacological characterization, single lab\",\n      \"pmids\": [\"39215006\"],\n      \"is_preprint\": false\n    }\n  ],\n  \"current_model\": \"TASK-3 (KCNK9/K2P9.1) is a two-pore domain background K+ channel that forms homodimers and heterodimers (with TASK-1, TWIK-1, and TASK-5) at the plasma membrane and in mitochondria; extracellular acidification inhibits the channel via His98 protonation triggering a cation-π interaction with Trp78 that drives C-type inactivation of the selectivity filter, as revealed by cryo-EM; voltage-dependent gating at the cytoplasmic mouth (X-gate) provides a second gating mechanism; channel trafficking to the surface requires 14-3-3 binding to a C-terminal phosphoserine (phosphorylated by PKA) that masks a COPI retention signal (KRR), while surface expression also depends on a di-acidic EDE ER-export motif and KCC2 interaction; volatile anesthetics activate the channel through Met159 at the transmembrane/C-terminus interface, the same region required for Gαq/neurotransmitter inhibition; PKCα phosphorylates Thr341 to reduce current while TNFα enhances gating through the ASK1/JNK/p38 pathway; oncogenic functions require intact K+ channel conductance, and mitochondrial TASK-3 regulates mitochondrial membrane potential and aldosterone synthesis in adrenal glomerulosa cells; loss-of-function mutations (especially G236R, which disrupts the X-gate) in the maternally expressed, paternally imprinted KCNK9 allele cause KCNK9 imprinting syndrome (Birk-Barel syndrome).\"\n}\n```","stage2_raw":"{\n  \"mechanistic_narrative\": \"KCNK9 (TASK-3/K2P9.1) encodes a two-pore-domain background K+ channel that conducts a time-independent, non-inactivating, pH-sensitive leak current setting resting membrane potential in excitable cells [#0, #1]. The channel is gated extracellularly by protons: His98 in the outer pore acts as the pH sensor [#0, #1], and cryo-EM at neutral and acidic pH shows that His98 protonation drives C-type inactivation by engaging a cation-\\u03c0 interaction with Trp78, dilating the selectivity-filter mouth while a hydrophobic gate blocks conduction [#32]; a second, lower cytoplasmic 'X-gate' provides voltage-dependent gating at the inner pore [#18, #33]. TASK-3 functions as a homodimer and assembles heterodimers with TASK-1, TWIK-1, and TASK-5, generating channels with intermediate pH sensitivity, distinct conductance, and altered pharmacology that account for native background currents in motoneurons, cerebellar granule neurons, and carotid body glomus cells [#2, #8, #27, #34, #17]. Surface delivery is tightly controlled: PKA phosphorylation of a C-terminal serine enables 14-3-3 binding that masks a tri-basic COPI retention signal (KRR), while a di-acidic EDE motif drives COPII-dependent ER export and KCC2 interaction supports membrane expression [#4, #16, #19, #12, #28]. Channel activity is modulated by an interface region at the transmembrane/C-terminus boundary that mediates both volatile-anesthetic activation (via Met159) and G\\u03b1q/neurotransmitter inhibition [#3, #20, #25], and PKC\\u03b1 phosphorylation of Thr341 reduces current [#13]. TASK-3 supports oncogenic proliferation and apoptosis resistance in a manner strictly dependent on intact K+ conductance [#6], and resides in mitochondria of adrenal zona glomerulosa cells where it controls mitochondrial membrane potential and aldosterone synthesis [#23]. Loss-of-function mutations in the maternally expressed, paternally imprinted KCNK9 allele\\u2014notably G236R, which disrupts the X-gate\\u2014cause KCNK9 imprinting (Birk-Barel) syndrome [#14, #33].\",\n  \"teleology\": [\n    {\n      \"year\": 2000,\n      \"claim\": \"Established that KCNK9 encodes a background K+ channel whose defining property is extracellular pH sensitivity, and pinpointed the molecular sensor.\",\n      \"evidence\": \"Heterologous expression with patch-clamp and His98 mutagenesis in COS-7, HEK293, and Xenopus oocytes\",\n      \"pmids\": [\"10734076\", \"10747866\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Structural basis of how His98 protonation closes the pore not yet resolved\", \"Native cellular roles unaddressed\"]\n    },\n    {\n      \"year\": 2001,\n      \"claim\": \"Showed TASK-3 is not obligately homodimeric but forms functional heterodimers with TASK-1, expanding the diversity of background currents it can generate.\",\n      \"evidence\": \"Xenopus oocyte co-expression and tandem-linked constructs with voltage clamp, plus immunofluorescence localization\",\n      \"pmids\": [\"11733509\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether heterodimers form in native tissue not yet shown\", \"Stoichiometry and assembly determinants undefined\"]\n    },\n    {\n      \"year\": 2002,\n      \"claim\": \"Mapped the C-terminal/transmembrane interface as the locus for anesthetic activation and neurotransmitter inhibition, and identified a 14-3-3-based trafficking checkpoint controlling surface expression.\",\n      \"evidence\": \"Site-directed mutagenesis with electrophysiology; yeast two-hybrid, Co-IP, and surface expression assays for 14-3-3\",\n      \"pmids\": [\"11886861\", \"12433946\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Identity of the retention signal masked by 14-3-3 not yet defined\", \"Kinase generating the 14-3-3 binding site unknown\"]\n    },\n    {\n      \"year\": 2002,\n      \"claim\": \"Linked TASK-3 to a physiological tissue role by showing it dominates the adrenal glomerulosa background conductance and is inhibited by angiotensin II receptor signaling.\",\n      \"evidence\": \"Northern blot, qRT-PCR, oocyte electrophysiology, and pharmacological matching to native current\",\n      \"pmids\": [\"11875121\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Native channel identity inferred pharmacologically, not by genetic ablation\", \"Downstream consequence for aldosterone not yet tested\"]\n    },\n    {\n      \"year\": 2003,\n      \"claim\": \"Demonstrated that the oncogenic activity of TASK-3 requires functional K+ conductance, linking channel biophysics directly to tumor biology.\",\n      \"evidence\": \"Pore mutant (G95E) with dominant-negative validation, proliferation/apoptosis assays, and nude mouse xenograft\",\n      \"pmids\": [\"12782791\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Signaling pathway connecting K+ flux to proliferation unresolved\", \"Tumor types dependent on TASK-3 not delineated\"]\n    },\n    {\n      \"year\": 2003,\n      \"claim\": \"Resolved the molecular site of ruthenium red block, defining Glu70 in the extracellular loop as a bridging site spanning both subunits.\",\n      \"evidence\": \"Tandem-construct mutagenesis with Hill analysis and gain-of-function transfer to TASK-1\",\n      \"pmids\": [\"12606773\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Physiological ligand for the Glu70 site not identified at this stage\"]\n    },\n    {\n      \"year\": 2004,\n      \"claim\": \"Confirmed TASK-1/TASK-3 heterodimers exist in native neurons and carry physiologically relevant currents, validating heteromerization beyond heterologous systems.\",\n      \"evidence\": \"Co-IP, dominant-negative suppression, tandem-construct and native motoneuron/granule-neuron patch-clamp with pharmacological profiling\",\n      \"pmids\": [\"15282272\", \"14678492\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Relative abundance of homo- vs heteromers in each cell type not quantified\", \"Functional consequence of heteromer-specific gating uncharacterized\"]\n    },\n    {\n      \"year\": 2006,\n      \"claim\": \"Generalized the Glu70 site as a polycation/divalent sensor and identified an activity-dependent transcriptional control of TASK-3 via Ca2+/calcineurin.\",\n      \"evidence\": \"Charge-swap mutagenesis with single-channel recording; depolarization paradigm with L-type channel/calcineurin blockade and RT-PCR\",\n      \"pmids\": [\"16513667\", \"16864570\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Transcription factor downstream of calcineurin not identified\", \"In vivo relevance of activity-dependent regulation untested\"]\n    },\n    {\n      \"year\": 2007,\n      \"claim\": \"Defined the ER-export and PKC regulatory mechanisms: a di-acidic EDE motif drives COPII-dependent export, and PKC\\u03b1 phosphorylation of Thr341 limits Gq-mediated inhibition.\",\n      \"evidence\": \"Surface expression assays, live imaging, Sar1 dominant-negative; phosphosite mutagenesis, PKC\\u03b1 siRNA, and G\\u03b1q antagonist with patch-clamp\",\n      \"pmids\": [\"17547699\", \"17374744\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"How EDE/COPII export integrates with downstream 14-3-3 checkpoint not unified\", \"Whether G\\u03b1q acts truly directly on the channel debated at the time\"]\n    },\n    {\n      \"year\": 2008,\n      \"claim\": \"Established loss-of-function as the disease mechanism for Birk-Barel syndrome and probed pore architecture by disulfide crosslinking the M1P1 loop to the pore.\",\n      \"evidence\": \"Electrophysiology of the G236R disease variant in homo/heterodimers; cysteine-substitution disulfide trapping between Glu70 and His98\",\n      \"pmids\": [\"18678320\", \"18417474\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Imprinting basis of maternal-allele effect not addressed here\", \"Structural gating change caused by G236R not yet visualized\"]\n    },\n    {\n      \"year\": 2009,\n      \"claim\": \"Defined dual gating (selectivity filter plus cytoplasmic gate) and refined the 14-3-3 trafficking model by identifying the masked COPI retention signal.\",\n      \"evidence\": \"Single-channel kinetic modeling with M2/M4/hinge mutagenesis; GST pulldown of COPI with the KRR motif and GFP localization in multiple systems; native carotid body single-channel comparison\",\n      \"pmids\": [\"19703964\", \"19139046\", \"19403596\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Atomic structure of the cytoplasmic gate not yet available\", \"Coupling between filter and cytoplasmic gates inferred from kinetics only\"]\n    },\n    {\n      \"year\": 2011,\n      \"claim\": \"Connected the trafficking checkpoint to a defined kinase and resolved the anesthetic activation residue, showing PKA-phosphorylated Ser373 enables 14-3-3-mediated export and Met159 forms the anesthetic site.\",\n      \"evidence\": \"In vitro kinase assay with surface GFP assay; M159C NEM modification with tandem dimers and electrophysiology\",\n      \"pmids\": [\"21357689\", \"22147752\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"In vivo kinase regulation of trafficking not tested\", \"Anesthetic binding pocket not structurally resolved at this point\"]\n    },\n    {\n      \"year\": 2013,\n      \"claim\": \"Localized TASK-3 to mitochondria of aldosterone-producing cells and tied it functionally to steroidogenesis, while refining the disease mutant as hypomorphic rather than null.\",\n      \"evidence\": \"Yeast two-hybrid, immunoprecipitation, EM, and TASK-3 knockout mouse mitochondrial/aldosterone phenotyping; electrophysiology of G236R with pharmacological rescue\",\n      \"pmids\": [\"28630209\", \"24342771\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Mechanism by which a K+ channel sets mitochondrial membrane potential unclear\", \"How residual G236R current relates to clinical severity unresolved\"]\n    },\n    {\n      \"year\": 2014,\n      \"claim\": \"Defined in vivo neuronal roles: TASK-3 sets cold-sensing thresholds in TRPM8 neurons and is the target of neurotensin-NTS1/G\\u03b1q signaling in dentate gyrus granule cells.\",\n      \"evidence\": \"TASK-3 knockout behavioral assays with FACS profiling of TRPM8 neurons; brain-slice patch-clamp with Co-IP showing NTS1-induced G\\u03b1q/TASK-3 association\",\n      \"pmids\": [\"25199828\", \"25405940\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether G\\u03b1q contacts the channel directly versus through an adaptor not fully settled\", \"Contribution of heteromers to these phenotypes not dissected\"]\n    },\n    {\n      \"year\": 2015,\n      \"claim\": \"Localized the binding site of breathing-stimulant inhibitors to the intracellular pore, identifying L122 and G236 as drug-contact residues.\",\n      \"evidence\": \"Homology modeling, docking, and mutagenesis with Ussing chamber electrophysiology for PKTHPP, A1899, and doxapram\",\n      \"pmids\": [\"26268529\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Site inferred from modeling/mutagenesis without a co-structure\", \"Selectivity over TASK-1 not addressed\"]\n    },\n    {\n      \"year\": 2018,\n      \"claim\": \"Identified TWIK-1 as a further heterodimeric partner of TASK-3 shaping dentate gyrus granule cell excitability.\",\n      \"evidence\": \"Co-IP from hippocampus and COS-7 cells, shRNA knockdown, and patch-clamp of granule cells\",\n      \"pmids\": [\"30416196\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Stoichiometry and gating of TWIK-1/TASK-3 heteromer not fully defined\", \"Single-lab Co-IP without structural confirmation\"]\n    },\n    {\n      \"year\": 2019,\n      \"claim\": \"Added KCC2 as a trafficking partner required for TASK-3 surface expression and characterized species- and pore-dependent doxapram pharmacology.\",\n      \"evidence\": \"Co-IP, KCC2 shRNA, fractionation, chemogenetic rescue, and patch-clamp; enantiomer and pore-residue mutagenesis with human/mouse comparison\",\n      \"pmids\": [\"31269453\", \"31423744\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Whether KCC2 acts via direct interaction or chaperone effect not fully resolved\", \"Structural basis of doxapram species selectivity unknown\"]\n    },\n    {\n      \"year\": 2020,\n      \"claim\": \"Showed that the natural compound withaferin A inhibits TASK-3 at defined pore residues and that its cytotoxicity in cancer cells is TASK-3-dependent, reinforcing the oncogenic relevance of the channel.\",\n      \"evidence\": \"Patch-clamp, docking, F125/L197 mutagenesis, and TASK-3 overexpression/knockdown viability assays in MDA-MB-231 cells\",\n      \"pmids\": [\"32563149\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Binding pose inferred from docking, not co-structure\", \"In vivo antitumor efficacy untested\"]\n    },\n    {\n      \"year\": 2022,\n      \"claim\": \"Broadened the disease genotype-phenotype map, showing KCNK9 imprinting syndrome arises from both gain and loss of conductance with altered regulatory control as the common theme.\",\n      \"evidence\": \"Electrophysiology of 15 variants with 3D molecular dynamics modeling and clinical/facial phenotyping\",\n      \"pmids\": [\"35698242\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Structural validation relied on modeling rather than experimental structures\", \"Mechanistic link between altered regulation and phenotype not established\"]\n    },\n    {\n      \"year\": 2024,\n      \"claim\": \"Provided the structural mechanism of pH gating and disease, resolving cryo-EM structures that show His98-Trp78 cation-\\u03c0-driven C-type inactivation and an X-gate disrupted by the G236R variant.\",\n      \"evidence\": \"Cryo-EM of TASK-3 at two pH states and of TASK-1/TASK-3 G236R, with MD simulations, mutagenesis, and electrophysiology; plus TASK-5/TASK-3 heterodimer characterization\",\n      \"pmids\": [\"38630723\", \"39637865\", \"39215006\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Structures of regulatory complexes (14-3-3, KCC2, G\\u03b1q) with the channel not yet determined\", \"Mitochondrial channel structure/function relationship unresolved\"]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"How the many regulatory inputs (PKA/14-3-3 trafficking, PKC\\u03b1, G\\u03b1q, KCC2, heteromerization) are integrated at the channel in vivo, and how K+ conductance is mechanistically coupled to oncogenesis and mitochondrial/aldosterone control, remains unresolved.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"No structure of TASK-3 bound to a trafficking or signaling partner\", \"Causal link between channel flux and proliferation undefined\", \"Mechanism by which a plasma-membrane-type K+ channel operates in mitochondria unknown\"]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0005215\", \"supporting_discovery_ids\": [0, 1, 6, 18, 32]},\n      {\"term_id\": \"GO:0140299\", \"supporting_discovery_ids\": [0, 1, 32]},\n      {\"term_id\": \"GO:0005267\", \"supporting_discovery_ids\": [0]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005886\", \"supporting_discovery_ids\": [2, 4, 12, 16, 34]},\n      {\"term_id\": \"GO:0005739\", \"supporting_discovery_ids\": [23]},\n      {\"term_id\": \"GO:0005783\", \"supporting_discovery_ids\": [12, 16, 19]},\n      {\"term_id\": \"GO:0005794\", \"supporting_discovery_ids\": [16]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"R-HSA-112316\", \"supporting_discovery_ids\": [8, 24, 25, 27]},\n      {\"term_id\": \"R-HSA-9609507\", \"supporting_discovery_ids\": [4, 12, 16, 19, 28]},\n      {\"term_id\": \"R-HSA-162582\", \"supporting_discovery_ids\": [13, 25]},\n      {\"term_id\": \"R-HSA-1643685\", \"supporting_discovery_ids\": [14, 22, 31]}\n    ],\n    \"complexes\": [\n      \"TASK-1/TASK-3 heterodimer\",\n      \"TWIK-1/TASK-3 heterodimer\",\n      \"TASK-5/TASK-3 heterodimer\"\n    ],\n    \"partners\": [\n      \"KCNK3\",\n      \"KCNK1\",\n      \"KCNK15\",\n      \"YWHAZ\",\n      \"SLC12A5\",\n      \"GNAQ\",\n      \"PRKCA\",\n      \"COPB1\"\n    ],\n    \"other_free_text\": []\n  }\n}","audit_flag":null,"evaluation":{"pairwise":"win","faith_supported":7,"faith_total":7,"faith_pct":100.0}}