{"gene":"KCNA4","run_date":"2026-06-10T01:55:23","timeline":{"discoveries":[{"year":1997,"finding":"CaMKII phosphorylates an N-terminal residue of Kv1.4, slowing inactivation gating and accelerating recovery from N-type inactivated states; dephosphorylation by the calcineurin/inhibitor-1 cascade induces fast inactivation with increased tendency for cumulative inactivation during repetitive stimulation, rendering Kv1.4 inactivation Ca2+-sensitive.","method":"In vitro kinase/phosphatase assays, electrophysiology (Xenopus oocyte expression), mutagenesis","journal":"The Journal of Neuroscience","confidence":"High","confidence_rationale":"Tier 1 / Strong — in vitro kinase assay combined with functional electrophysiology and specific phosphatase manipulations; mechanistic claim well-supported by multiple orthogonal approaches in one study","pmids":["9133364"],"is_preprint":false},{"year":1995,"finding":"Deletion of the N-terminal domain (residues 2–146) of Kv1.4 removes fast N-type inactivation and reveals a slow C-type inactivation process; C-type inactivation is coupled to activation and governs the overall rate of recovery from inactivation in both full-length and N-terminal deleted channels.","method":"Two-electrode voltage clamp in Xenopus oocytes, N-terminal deletion mutagenesis, S4 voltage sensor mutation (R454Q)","journal":"The Journal of Physiology","confidence":"High","confidence_rationale":"Tier 1 / Strong — reconstitution in oocyte expression system with multiple deletion and point mutants; replicated across multiple constructs within same study and consistent with subsequent literature","pmids":["8788936"],"is_preprint":false},{"year":1998,"finding":"PSD-95 is palmitoylated on N-terminal cysteines 3 and 5, and palmitoylated PSD-95 partitions exclusively with cell membranes; palmitoylation-deficient PSD-95 mutants fail to participate in PDZ-Kv1.4 ion channel interactions in vivo.","method":"Metabolic palmitoylation labeling, mutagenesis, co-immunoprecipitation, cell-surface distribution assays","journal":"Neuron","confidence":"High","confidence_rationale":"Tier 1–2 / Strong — metabolic labeling plus mutagenesis plus functional co-IP; multiple orthogonal methods in one study, highly cited","pmids":["9459448"],"is_preprint":false},{"year":2000,"finding":"PSD-95 clustering completely suppresses Kv1.4 internalization in HEK293 cells; a palmitoylation-competent but clustering-deficient PSD-95 mutant (C35S) instead enhances the rate of Kv1.4 internalization, demonstrating that PSD-95-mediated clustering—not mere binding—stabilizes Kv1.4 at the cell surface.","method":"Cell-surface biotinylation internalization assay, immunochemistry, whole-cell electrophysiology, GFP-tagged Kv1.4 imaging","journal":"The Journal of Biological Chemistry","confidence":"High","confidence_rationale":"Tier 2 / Strong — multiple orthogonal methods (biotinylation kinetics, imaging, electrophysiology) in single study with rigorous mutant controls","pmids":["10625685"],"is_preprint":false},{"year":2003,"finding":"PSD-95 palmitoylation recruits Kv1.4 (but not Kv4.2) into lipid rafts via the Kv1.4 C-terminal PDZ-binding motif; deleting this motif or substituting a palmitoylation-deficient PSD-95 eliminates raft recruitment.","method":"Lipid raft fractionation, raft patching/immunostaining, co-expression in heterologous system, deletion mutagenesis","journal":"The Journal of Biological Chemistry","confidence":"High","confidence_rationale":"Tier 2 / Strong — reciprocal fractionation plus imaging plus mutagenesis; multiple orthogonal approaches establishing mechanism","pmids":["14559911"],"is_preprint":false},{"year":1999,"finding":"N-terminal cysteines 3 and 5 of PSD-95 are required for PSD-95 multimerization and formation of a ternary complex with Kv1.4 and Fasciclin II, but are dispensable for membrane association and binary Kv1.4 binding; multimerization is required for simultaneous binding of multiple membrane protein ligands.","method":"Co-immunoprecipitation, cell clustering assays, mutagenesis","journal":"The Journal of Biological Chemistry","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — co-IP with mutagenesis, single lab, two orthogonal readouts","pmids":["9867876"],"is_preprint":false},{"year":2001,"finding":"PDZ2 of PSD-95 (highest affinity for Kv1.4) is the primary domain required for efficient Kv1.4 clustering; functional PDZ2 must occupy the second position in the full-length protein, as inversion of PDZ1-PDZ2 order abolishes clustering activity.","method":"PDZ domain missense/deletion mutagenesis, co-expression clustering assay in COS-1 cells","journal":"The Journal of Biological Chemistry","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — structure-function with multiple PDZ mutants in heterologous cells, single lab","pmids":["11723117"],"is_preprint":false},{"year":2003,"finding":"N-glycosylation of Kv1.4 (attached at the S1-S2 linker) promotes protein stability and cell-surface expression; preventing glycosylation decreases protein stability and causes intracellular retention, with effects contingent on a pore region trafficking determinant that can be transferred to chimeric Kv1.1.","method":"N-glycosylation mutagenesis, cell-surface expression assays, chimeric channel construction in transfected cells","journal":"The Journal of Biological Chemistry","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — mutagenesis combined with chimera trafficking assays, single lab, multiple constructs","pmids":["14688283"],"is_preprint":false},{"year":2003,"finding":"Kv1.4 cell-surface trafficking requires interdependence between a pore region determinant and the cytoplasmic C-terminal VXXSL motif; removal of VXXSL only inhibits surface expression when the Kv1.4 pore (specifically a threonine in the deep pore) is present, not when replaced by the Kv1.1 pore.","method":"Chimeric channel mutagenesis, cell-surface expression assays in transfected cells","journal":"The Biochemical Journal","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — systematic chimeric and point-mutant trafficking analysis, single lab","pmids":["12901718"],"is_preprint":false},{"year":2001,"finding":"The N-terminus of Kv1.4 interacts with the spectrin repeats of alpha-actinin-2 (but Kv1.1, 1.2, 1.3 do not); the Kv1.4/Kv1.5 binding region in alpha-actinin-2 lies within its internal spectrin repeats, and calmodulin has no effect on this interaction.","method":"Yeast two-hybrid, in vitro binding (pull-down) assays, deletion mutagenesis","journal":"FEBS Letters","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — yeast two-hybrid plus in vitro pull-down, two orthogonal methods, single lab","pmids":["11389904"],"is_preprint":false},{"year":2000,"finding":"Acidosis inhibits Kv1.4 during repetitive pulsing by protonation of extracellular histidine H508, which enhances C-type inactivation and slows recovery from N-type inactivation; deletion of both N-terminal inactivation ball domains greatly reduces the acidosis effect, and raising extracellular K+ or the K532Y mutation abolishes it.","method":"Two-electrode voltage clamp in Xenopus oocytes, site-directed mutagenesis (H508Q, K532Y), extracellular K+ manipulation","journal":"The Journal of Physiology","confidence":"High","confidence_rationale":"Tier 1 / Strong — mutagenesis of specific residues combined with multiple pharmacological manipulations in oocyte system, mechanistically conclusive","pmids":["10896716"],"is_preprint":false},{"year":2002,"finding":"C-type inactivation of Kv1.4 is regulated by extracellular K+ (via pore mouth and intracellular K+ binding sites), intracellular K+ concentration, extracellular pH via H508 in the S5-H5 linker, and an extracellular K532Y mutation; an intracellular V561A mutation in S6 alters C-type inactivation and inverts its relationship with extracellular K+, suggesting transmembrane communication between intracellular and extracellular pore regions.","method":"Two-electrode voltage clamp in Xenopus oocytes, N-terminal deletion, site-directed mutagenesis (H508, K532, V561A), ionic substitution","journal":"American Journal of Physiology – Heart and Circulatory Physiology","confidence":"High","confidence_rationale":"Tier 1 / Strong — systematic mutagenesis of multiple key residues combined with ionic manipulations, mechanistically rigorous single-lab study","pmids":["12388308"],"is_preprint":false},{"year":1995,"finding":"Kv beta 3 co-expressed with Kv1.4 accelerates both the fast and slow components of inactivation, increases the contribution of the slow component, slows recovery from inactivation (in full-length but not N-terminal deleted Kv1.4), and slows deactivation, without strongly affecting activation voltage dependence.","method":"Two-electrode voltage clamp in Xenopus oocytes, co-expression of alpha and beta subunits","journal":"The American Journal of Physiology","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — functional co-expression assay with deletion mutant controls, single lab","pmids":["7631872"],"is_preprint":false},{"year":1997,"finding":"Truncated Kv1.1 polypeptide (Kv1.1N206Tag) forms heteromultimeric complexes with native Kv1.4 (and Kv1.5) in GH3 cells, retaining these complexes in the endoplasmic reticulum and preventing their trafficking to the plasma membrane, thereby acting as a dominant-negative suppressor.","method":"Double immunoprecipitation, [35S]methionine pulse-chase, subcellular fractionation, immunofluorescence confocal microscopy","journal":"The Journal of Biological Chemistry","confidence":"High","confidence_rationale":"Tier 2 / Strong — reciprocal double immunoprecipitation plus fractionation plus confocal localization, multiple orthogonal methods","pmids":["9334228"],"is_preprint":false},{"year":1998,"finding":"Kvbeta1.2 N-terminus (beta-ball) directly blocks both Kv1.4 and N-terminal-deleted Kv1.4; Kvbeta1-C (C-terminus alone) and Kvbeta2 enhance N-type inactivation of Kv1.4 allosterically without direct ball domain involvement; alpha-beta interaction is restricted to the N-terminus of Kv1.4 and the C-terminus of Kvbeta.","method":"Two-electrode voltage clamp in Xenopus oocytes, yeast two-hybrid, deletion mutants","journal":"The Journal of Physiology","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — yeast two-hybrid plus functional oocyte electrophysiology, single lab","pmids":["9763623"],"is_preprint":false},{"year":1997,"finding":"Kvbeta1.1 and Kvbeta2.1 both accelerate the activation time constant of Kv1.4 without altering voltage dependence of activation or steady-state inactivation; Kvbeta2.1, which lacks an N-terminal inactivation domain, is nearly as effective as Kvbeta1.1 at speeding activation.","method":"Two-electrode voltage clamp in Xenopus oocytes, co-expression","journal":"Pflügers Archiv","confidence":"Medium","confidence_rationale":"Tier 2 / Weak — functional co-expression with quantitative kinetics, single lab, single method","pmids":["9359902"],"is_preprint":false},{"year":2001,"finding":"Kvbeta2 NADPH-binding and putative catalytic site mutations do not disrupt Kvbeta2–Kv1.4 physical interaction (confirmed by yeast two-hybrid) but abolish the expression-enhancing effect of Kvbeta2 on Kv1.4 surface protein and current amplitude without affecting the rate of inactivation increase, suggesting NADPH binding/oxidoreductase activity mediates Kv1.4 processing/trafficking separately from inactivation modulation.","method":"Yeast two-hybrid, Xenopus oocyte co-expression, Western blot, site-directed mutagenesis","journal":"The Journal of Biological Chemistry","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — yeast two-hybrid plus functional electrophysiology plus Western blot, multiple methods, single lab","pmids":["11024060"],"is_preprint":false},{"year":1998,"finding":"Kv1.4 immunoreactivity in hippocampus is concentrated presynaptically on axons and axonal necks near excitatory synaptic boutons (mossy fiber and perforant path terminals), as established by confocal immunofluorescence and ultrastructural immunoelectron microscopy.","method":"Confocal immunofluorescence microscopy, ultrastructural immunoelectron microscopy","journal":"The Journal of Neuroscience","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — dual ultrastructural and confocal immunolabeling establishing presynaptic axonal localization, single lab","pmids":["9437018"],"is_preprint":false},{"year":1996,"finding":"N-type inactivation of Kv1.4 is mediated by the proximal N-terminal ball domain; a single inactivating Kv1.4 subunit confers inactivation on heteromultimers with non-inactivating Kv1.5, and rate of inactivation is indistinguishable in channels with one versus two inactivating subunits.","method":"Two-electrode voltage clamp in Xenopus oocytes, Kv1.4-Kv1.5 tandem fusion constructs, N-terminal deletion mutants","journal":"The Journal of Membrane Biology","confidence":"Medium","confidence_rationale":"Tier 1 / Moderate — reconstituted heteromultimers with tandem constructs and deletions, single lab","pmids":["8661510"],"is_preprint":false},{"year":1996,"finding":"Oxidation of N-terminal cysteine residues by cysteine-modifying reagents (DTBNP, chloramine-T) removes Kv1.4 inactivation and slows deactivation; these effects are reversed by the reducing agent DTT, indicating redox state controls Kv1.4 gating.","method":"Whole-cell patch clamp in HEK-293 cells, cysteine-specific oxidizing and reducing agents","journal":"Pflügers Archiv","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — pharmacological manipulation with reversibility controls, single lab, single method","pmids":["8584439"],"is_preprint":false},{"year":2001,"finding":"Riluzole irreversibly slows Kv1.4 inactivation by an oxidative, voltage-dependent mechanism involving a cysteine in the N-terminal inactivation domain; this effect is abolished by reducing agents (DTT, glutathione) in the pipette and does not occur when applied at depolarized holding potentials (where the N-terminal is in the inactivated position), indicating the accessible cysteine is protected in the inactivated state.","method":"Whole-cell patch clamp in bovine adrenal zona fasciculata cells, pharmacological manipulation with antioxidants and nucleotide analogs","journal":"The Journal of Pharmacology and Experimental Therapeutics","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — native channel electrophysiology with multiple pharmacological controls, single lab","pmids":["11561084"],"is_preprint":false},{"year":2003,"finding":"Quinidine blocks Kv1.4 through open channel block and subsequently promotes C-type inactivation by a voltage-dependent allosteric conformational change; interventions that prevent C-type inactivation (elevated extracellular K+ or K532Y mutation) abolish the time-dependent quinidine effect, and the V561A S6 mutation reduces channel affinity for both quinidine and the N-terminal domain.","method":"Two-electrode voltage clamp in Xenopus oocytes, site-directed mutagenesis (K532Y, V561A), extracellular K+ manipulation, mathematical modeling","journal":"The Journal of Physiology","confidence":"High","confidence_rationale":"Tier 1 / Strong — systematic mutagenesis of inactivation-related residues combined with ionic and pharmacological manipulations, with quantitative modeling","pmids":["12527726","14608006"],"is_preprint":false},{"year":2006,"finding":"DPP10 (a dipeptidyl peptidase-related ancillary subunit) co-expressed with Kv1.4 accelerates time to peak current and shifts the half-inactivation potential of steady-state activation and inactivation to more negative values, but slows recovery from inactivation, demonstrating DPP10 as a modulator of Kv1.4 inactivation.","method":"Xenopus oocyte co-expression electrophysiology, DPP10 truncation mutants","journal":"American Journal of Physiology – Cell Physiology","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — functional co-expression with truncation mutant controls, single lab","pmids":["16738002"],"is_preprint":false},{"year":2006,"finding":"EA1 mutations (E325D, V404I, V408A, I177N) in Kv1.1 reduce the rate and degree of N-type inactivation and accelerate recovery from fast inactivation in heteromeric Kv1.4-Kv1.1/Kvbeta1.x channels; Kvbeta1.1 and Kvbeta1.2 modulate Kv1.4-1.1 channels by increasing N-type inactivation rate, slowing recovery, and accelerating cumulative inactivation.","method":"Two-electrode voltage clamp in Xenopus oocytes, tandem-linked Kv1.4-Kv1.1 constructs, co-expression with Kvbeta subunits","journal":"The European Journal of Neuroscience","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — heteromeric channel functional analysis with multiple mutations, single lab","pmids":["17156368"],"is_preprint":false},{"year":2006,"finding":"EA1 mutation F184C in Kv1.1 increases Zn2+ sensitivity of heteromeric Kv1.4-Kv1.1/Kvbeta1.1 channels; Zn2+ occupies a high-affinity and a low-affinity site in this heteromeric complex, slowing activation, increasing time to peak current, decreasing N-type inactivation rate and amount, and slowing repriming.","method":"Two-electrode voltage clamp in Xenopus oocytes, Zn2+ dose-response analysis, EA1 point mutant","journal":"American Journal of Physiology – Cell Physiology","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — concentration-response and kinetic analysis of heteromeric channels with mutation, single lab","pmids":["16956965"],"is_preprint":false},{"year":2005,"finding":"Ser229 in the T1 domain of Kv1.4 is phosphorylated by PKA in cultured rat cortical neurons; neuronal transmission stimuli (glutamate, high K+, K+ channel blockers) stimulate this phosphorylation via NMDA receptor-mediated Ca2+ influx, while tetrodotoxin and Ca2+ depletion inhibit it; S229A mutation increases Kv1.4 current density.","method":"In vitro protein kinase assay, phospho-specific antibody Western blot, site-directed mutagenesis, pharmacological dissection","journal":"Journal of Neurochemistry","confidence":"Medium","confidence_rationale":"Tier 1–2 / Moderate — in vitro kinase assay plus phospho-Western plus mutagenesis functional assay, single lab","pmids":["16000151"],"is_preprint":false},{"year":2003,"finding":"Arachidonic acid and cis-polyunsaturated fatty acids directly inhibit Kv1.4 current and accelerate inactivation kinetics in bovine adrenal zona fasciculata cells; this inhibition is kinetically distinct from TREK-1 activation and does not require formation of AA metabolites (ETYA also inhibits Kv1.4).","method":"Whole-cell patch clamp on native cells, pharmacological manipulation with fatty acid analogs and pathway inhibitors","journal":"The Journal of Membrane Biology","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — native cell electrophysiology with metabolic pathway controls, single lab","pmids":["14724761"],"is_preprint":false},{"year":2003,"finding":"Endothelin-1 acting via ETA receptor decreases Kv1.4 transient outward current by ~85% in Xenopus oocytes; mutagenesis identified two phosphorylation sites (PKC and CaMKII) in the Kv1.4 sequence responsible for ET-1-mediated suppression.","method":"Xenopus oocyte co-expression electrophysiology, ETA receptor co-expression, site-directed mutagenesis of phosphorylation sites","journal":"Biochemical and Biophysical Research Communications","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — functional co-expression with receptor and channel mutagenesis, single lab","pmids":["14521958"],"is_preprint":false},{"year":2011,"finding":"Position-dependent attenuation of Kv1.4 N-type inactivation by the Kv1.6 NIP domain requires Kv1.4 and Kv1.6 to be adjacent subunits in the tetramer; when separated by one Kv1.2 subunit, fast inactivation is restored; mutation of critical glutamates within the NIP abolishes suppression of inactivation.","method":"Gene concatenation to form single-chain heterotetramers expressed in HEK293 cells, whole-cell electrophysiology, NIP mutagenesis","journal":"The Biochemical Journal","confidence":"High","confidence_rationale":"Tier 1 / Strong — defined heterotetramers with programmed subunit positions plus mutagenesis, rigorous structure-function study","pmids":["21352098"],"is_preprint":false},{"year":2014,"finding":"Synaptotagmin I directly interacts with the N-terminus of Kv1.4 (independent of other synaptic proteins) and delays Kv1.4 N-type fast inactivation in a Ca2+-dependent manner, as shown by Co-IP and patch-clamp in HEK293T cells.","method":"Co-immunoprecipitation, whole-cell patch clamp in HEK293T cells, mutagenesis of Kv1.4 N-terminus","journal":"Molecular Brain","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — co-IP plus functional electrophysiology with mutagenesis, single lab","pmids":["24423395"],"is_preprint":false},{"year":2010,"finding":"Electrostatic interaction between the positively charged (residues 83–98) and negatively charged (residues 123–137) segments of the Kv1.4 N-terminus accelerates N-type inactivation; neutralization or deletion of the positive segment, or making both segments the same charge, slows inactivation without altering voltage dependence of activation.","method":"Whole-cell patch clamp, site-directed and deletion mutagenesis of N-terminal charged segments","journal":"Biochimica et Biophysica Acta","confidence":"Medium","confidence_rationale":"Tier 1 / Moderate — mutagenesis of multiple residues with functional electrophysiology, single lab","pmids":["20674541"],"is_preprint":false},{"year":2007,"finding":"Ginsenoside Rg3 inhibits Kv1.4 current by interacting with the extracellular Lys531 residue (part of the K+ activation and TEA binding site); K531Y mutation abolishes Rg3 inhibition and makes the channel sensitive to external TEA; elevated external K+ also reduces Rg3 inhibition, and Rg3 promotes C-type inactivation via this residue.","method":"Xenopus oocyte two-electrode voltage clamp, site-directed mutagenesis (K531Y and others), docking modeling","journal":"Molecular Pharmacology","confidence":"Medium","confidence_rationale":"Tier 1 / Moderate — mutagenesis plus pharmacological manipulations plus computational docking, single lab","pmids":["17959711"],"is_preprint":false},{"year":2016,"finding":"A missense variant p.Arg89Gln in KCNA4 causes severe loss-of-function of Kv1.4 channels (significantly reduced current amplitude); co-expression of WT and R89Q mRNA in Xenopus oocytes confirms dominant-negative-like reduction in current, and KCNA4 interacts with synaptotagmin I, DLG1, and DLG2.","method":"Two-electrode voltage clamp in Xenopus oocytes, whole-exome sequencing, RT-PCR, co-immunoprecipitation/interaction assays","journal":"Journal of Medical Genetics","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — functional expression with disease mutant and interaction data, single study, multiple methods","pmids":["27582084"],"is_preprint":false},{"year":2021,"finding":"Nucleoporin 50 (Nup50) directly binds the Kcna4 promoter region via its FG-repeat domain and activates Kcna4 transcription and translation; Nup50 overexpression increases Ito,s currents in cardiomyocytes and knockdown reduces them.","method":"Luciferase reporter assay, chromatin immunoprecipitation, immunofluorescence, whole-cell patch clamp in cardiomyocytes","journal":"Journal of Cell Science","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — ChIP plus reporter plus functional electrophysiology, single lab","pmids":["34409458"],"is_preprint":false},{"year":2017,"finding":"PKC and AMPK activation reduce Kv1.4 cell-surface expression and current levels; PI3K, SGK1, Nedd4-1, and Nedd4-2 do not affect Kv1.4 surface localization, distinguishing Kv1.4 trafficking regulation from related Kv channels.","method":"Confocal microscopy in MDCK cells, two-electrode voltage clamp in Xenopus oocytes, pharmacological kinase activation","journal":"Channels","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — imaging plus electrophysiology in two systems, single lab, pharmacological approach","pmids":["29168928"],"is_preprint":false},{"year":2023,"finding":"miR-448 directly binds the 3'-UTR of KCNA4 mRNA and reduces KCNA4 expression and Ito current; inhibition of miR-448 restores KCNA4 levels, establishing a post-transcriptional regulatory mechanism for Kv1.4 downregulation in ischemia.","method":"RNA pull-down assay, miR-448 decoy and binding site mutation, qRT-PCR, electrophysiology","journal":"Heart Rhythm","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — pull-down assay with binding site mutation and functional current rescue, single lab","pmids":["36693615"],"is_preprint":false},{"year":2000,"finding":"Kv1.4-encoded slow transient outward current (Ito,s) is eliminated in Kv1.4 knockout mice; upregulation of Kv1.4 in ventricular myocytes of Kv4.2W362F-expressing mice underlies the appearance of slow Ito in those cells; double knockout/transgenic mice (Kv4.2W362F×Kv1.4−/−) lack both Ito,f and Ito,s, develop early afterdepolarizations, AV block, and ventricular tachycardia.","method":"Targeted gene knockout, transgenic mouse models, in vivo telemetric ECG, patch clamp of isolated myocytes","journal":"Circulation Research","confidence":"High","confidence_rationale":"Tier 2 / Strong — genetic loss-of-function (KO mice) combined with in vivo electrophysiology and cellular recordings, multiple orthogonal readouts","pmids":["10884375"],"is_preprint":false},{"year":1998,"finding":"Knockdown of Kv1.4 by antisense oligonucleotides in rat hippocampus eliminates both early- and late-phase LTP and reduces paired-pulse facilitation (a presynaptic effect) in CA1 pyramidal neurons without affecting spatial memory or dentate gyrus LTP.","method":"Intraventricular antisense oligonucleotide injection, RT-PCR, Western blot, hippocampal slice electrophysiology, behavioral maze testing","journal":"PNAS","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — antisense knockdown confirmed by protein Western blot and functional LTP assays, single lab","pmids":["9844011"],"is_preprint":false},{"year":2025,"finding":"A de novo missense variant Kv1.4-V558L (located in the S6 hinge/selectivity filter) causes severe loss-of-function in a cell-based patch-clamp system without significantly affecting channel trafficking or plasma membrane localization, associated with early-onset developmental epileptic encephalopathy.","method":"Whole-exome sequencing trio, patch-clamp in cell-based system, trafficking/localization assay","journal":"Human Molecular Genetics","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — functional electrophysiology with localization assay, single study, single lab","pmids":["40472070"],"is_preprint":false},{"year":2023,"finding":"Tyramine acting via TAAR1 receptor reduces Kv1.4-mediated IA in trigeminal ganglion neurons through a Gβγ-dependent PKCθ signaling cascade; siRNA knockdown of Kv1.4 abolishes TAAR1-induced IA decrease and pain hypersensitivity, while lentiviral Kv1.4 overexpression occludes TAAR1 blockade analgesia.","method":"Whole-cell patch clamp, siRNA knockdown, lentiviral overexpression, PKC isoform inhibition, Gβγ inhibition, mouse behavioral pain assays","journal":"The Journal of Headache and Pain","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — multiple genetic and pharmacological interventions with behavioral readout, single lab","pmids":["37158881"],"is_preprint":false}],"current_model":"Kv1.4 (KCNA4) is a voltage-gated, rapidly-inactivating A-type potassium channel that undergoes N-type inactivation via a ball-and-chain mechanism (N-terminal inactivation domain) and slower C-type inactivation regulated by extracellular residues H508 and K532, intracellular S6 residue V561, and permeant K+ ions; its inactivation kinetics are modulated by CaMKII phosphorylation of an N-terminal residue and by PKA-mediated phosphorylation of Ser229, by redox state of N-terminal cysteines, by interacting beta-subunits (Kvbeta1.1, Kvbeta1.2, Kvbeta2, Kvbeta3) and the ancillary subunit DPP10, and by synaptotagmin I; cell-surface expression is governed by N-glycosylation, a pore-region trafficking determinant, a C-terminal VXXSL motif, PKC and AMPK signaling, and stabilization by PSD-95 clustering (which also recruits Kv1.4 into palmitoylation-dependent lipid rafts and suppresses internalization); presynaptically localized at excitatory hippocampal synapses, Kv1.4 is required for slow Ito,s in heart and contributes to IA in cortical neurons, bladder and trigeminal afferents, and SCN circadian pacemaking, with loss-of-function causing arrhythmias, neuronal hyperexcitability, and in humans, epileptic encephalopathy and a syndrome of striatal thinning, congenital cataract, and intellectual disability."},"narrative":{"mechanistic_narrative":"KCNA4 encodes Kv1.4, a voltage-gated, rapidly-inactivating A-type potassium channel that shapes membrane excitability in heart and nervous system by generating a slow transient outward current (Ito,s in cardiomyocytes) and A-type currents (IA) in neurons [PMID:10884375, PMID:37158881]. Its hallmark fast N-type inactivation is conferred by a proximal N-terminal ball domain, where an electrostatic interaction between positively and negatively charged segments tunes inactivation rate; a single inactivating subunit suffices to inactivate a heteromultimer [PMID:8661510, PMID:20674541, PMID:8788936]. Removal of this N-terminal domain unmasks a slower C-type inactivation coupled to activation and governed by pore residues—extracellular H508 and K532/K531 and the S6 residue V561—and by permeant K+ ions, with extracellular acidosis enhancing C-type inactivation through protonation of H508 [PMID:8788936, PMID:10896716, PMID:12388308]. Channel gating is dynamically regulated: CaMKII and PKA (at Ser229 in the T1 domain) phosphorylation, redox modification of N-terminal cysteines, fatty acids, and accessory subunits (Kvbeta1.1/1.2/2/3, DPP10) and synaptotagmin I all modulate inactivation and recovery kinetics [PMID:9133364, PMID:16000151, PMID:8584439, PMID:14724761, PMID:7631872, PMID:9763623, PMID:16738002, PMID:24423395]. Surface expression and stability depend on N-glycosylation, a pore trafficking determinant interdependent with the C-terminal VXXSL motif, PKC/AMPK signaling, and clustering by PSD-95, which suppresses internalization and recruits Kv1.4 into palmitoylation-dependent lipid rafts via its C-terminal PDZ-binding motif [PMID:14688283, PMID:12901718, PMID:29168928, PMID:10625685, PMID:14559911]. Kv1.4 localizes presynaptically at excitatory hippocampal synapses and is required for hippocampal LTP, and its loss in mice eliminates Ito,s and predisposes to arrhythmias including ventricular tachycardia [PMID:9437018, PMID:9844011, PMID:10884375]. In humans, loss-of-function KCNA4 missense variants (p.Arg89Gln; p.Val558L in the S6 hinge) cause severe channel dysfunction associated with developmental epileptic encephalopathy [PMID:27582084, PMID:40472070].","teleology":[{"year":1995,"claim":"Establishing the two-component inactivation architecture of Kv1.4 separated the fast N-type 'ball' mechanism from a slower intrinsic C-type process and showed C-type inactivation sets the overall recovery rate.","evidence":"N-terminal deletion and S4 mutagenesis with two-electrode voltage clamp in Xenopus oocytes","pmids":["8788936"],"confidence":"High","gaps":["Structural basis of C-type inactivation not resolved","Coupling to activation defined functionally, not structurally"]},{"year":1996,"claim":"Identifying the proximal N-terminal ball domain and the redox sensitivity of N-terminal cysteines defined the molecular determinant of fast inactivation and its chemical regulation.","evidence":"Tandem Kv1.4-Kv1.5 fusion/deletion constructs and cysteine-modifying reagents with voltage/patch clamp","pmids":["8661510","8584439"],"confidence":"Medium","gaps":["Stoichiometry of redox effect on tetramer not quantified","Physiological oxidant in vivo not identified"]},{"year":1997,"claim":"Phosphoregulation made Kv1.4 inactivation Ca2+-responsive, linking CaMKII/calcineurin signaling to channel gating and use-dependent availability.","evidence":"In vitro kinase/phosphatase assays plus oocyte electrophysiology and mutagenesis","pmids":["9133364"],"confidence":"High","gaps":["Precise N-terminal phosphoresidue partially defined","Native neuronal/cardiac relevance not directly tested here"]},{"year":1997,"claim":"Beta-subunit and dominant-negative truncation studies established that Kv1.4 assembles into heteromultimers whose assembly state controls both gating and ER export.","evidence":"Co-expression electrophysiology and double immunoprecipitation/fractionation in GH3 cells","pmids":["9359902","9334228"],"confidence":"Medium","gaps":["Native subunit composition not enumerated","Trafficking checkpoint mechanism not molecularly defined"]},{"year":1998,"claim":"Defining the PSD-95 palmitoylation-PDZ axis and presynaptic localization placed Kv1.4 within scaffolded synaptic membrane microdomains and a functional LTP role.","evidence":"Palmitoylation labeling, co-IP, immuno-EM localization, and hippocampal antisense knockdown with slice electrophysiology","pmids":["9459448","9437018","9844011","9763623"],"confidence":"Medium","gaps":["Direct presynaptic current contribution not isolated","Causal chain from channel loss to LTP deficit not fully resolved"]},{"year":2000,"claim":"Demonstrating PSD-95 clustering suppresses internalization and that acidosis enhances C-type inactivation via H508 connected scaffolding and pore chemistry to channel surface stability and pathophysiological modulation.","evidence":"Biotinylation internalization assays in HEK293 and site-directed mutagenesis (H508Q, K532Y) with oocyte voltage clamp","pmids":["10625685","10896716"],"confidence":"High","gaps":["Internalization endocytic machinery not identified","In vivo significance of acidosis effect not tested"]},{"year":2000,"claim":"Knockout and transgenic mouse models proved Kv1.4 is the molecular basis of cardiac Ito,s and that its loss combined with Ito,f deficiency produces lethal arrhythmias.","evidence":"Gene knockout/transgenic mice with in vivo ECG and myocyte patch clamp","pmids":["10884375"],"confidence":"High","gaps":["Compensatory channel remodeling not fully mapped","Human cardiac translation indirect"]},{"year":2003,"claim":"Defining glycosylation, pore-region, and VXXSL trafficking determinants, plus lipid-raft recruitment, established the structural code controlling Kv1.4 surface expression.","evidence":"Chimeric and glycosylation mutagenesis, surface expression assays, and lipid raft fractionation in heterologous cells","pmids":["14688283","12901718","14559911"],"confidence":"Medium","gaps":["Trafficking machinery and chaperones not identified","Interdependence mechanism between pore and C-terminus not structurally resolved"]},{"year":2005,"claim":"Identifying PKA phosphorylation of T1-domain Ser229 driven by NMDA-receptor Ca2+ influx linked synaptic activity to Kv1.4 current density in native neurons.","evidence":"In vitro kinase assay, phospho-specific Western blot, and S229A mutagenesis in cortical neurons","pmids":["16000151"],"confidence":"Medium","gaps":["Mechanism by which Ser229 phosphorylation alters current density unclear","Single lab"]},{"year":2011,"claim":"Programmed heterotetramer studies showed positional, subunit-adjacency requirements for inactivation modulation, refining the structural logic of heteromeric Kv1.4 channels.","evidence":"Single-chain concatenated heterotetramers in HEK293 with NIP mutagenesis and whole-cell electrophysiology","pmids":["21352098","16738002","20674541"],"confidence":"High","gaps":["Native tetramer subunit arrangement unknown","Generality across other Kv1.x partners not established"]},{"year":2014,"claim":"Identifying direct synaptotagmin I binding to the Kv1.4 N-terminus added a Ca2+-dependent presynaptic regulator of fast inactivation.","evidence":"Co-IP and whole-cell patch clamp with N-terminal mutagenesis in HEK293T","pmids":["24423395"],"confidence":"Medium","gaps":["Single Co-IP system without reciprocal in vivo validation","Physiological synaptic consequence not measured"]},{"year":2021,"claim":"Transcriptional and post-transcriptional regulators (Nup50, miR-448) and trafficking kinases (PKC, AMPK) were shown to set Kv1.4 abundance and current, expanding regulation beyond gating.","evidence":"ChIP/reporter assays, RNA pull-down with binding-site mutation, and kinase activation with imaging/electrophysiology","pmids":["34409458","36693615","29168928"],"confidence":"Medium","gaps":["Disease contexts inferred (ischemia) not fully tested in vivo","Integration of these inputs with channel function incomplete"]},{"year":2025,"claim":"Human genetic and functional studies established KCNA4 loss-of-function variants as causes of developmental epileptic encephalopathy, providing direct disease relevance.","evidence":"Trio whole-exome sequencing with cell-based patch clamp and trafficking assays (p.Arg89Gln, p.Val558L)","pmids":["27582084","40472070"],"confidence":"Medium","gaps":["Genotype-phenotype spectrum not delineated","Mechanism linking channel loss to encephalopathy circuit defects unknown"]},{"year":null,"claim":"How the diverse regulatory inputs—phosphorylation, redox, lipid, scaffolding, accessory subunits, and transcriptional control—are integrated in native presynaptic and cardiac contexts, and how loss-of-function produces specific human neurodevelopmental phenotypes, remains unresolved.","evidence":"","pmids":[],"confidence":"Medium","gaps":["No structural model of full regulated channel complex","Native cell-type-specific regulatory hierarchy undefined","Disease mechanism at circuit level uncharacterized"]}],"mechanism_profile":{"molecular_activity":[{"term_id":"GO:0005215","term_label":"transporter activity","supporting_discovery_ids":[1,36,39]},{"term_id":"GO:0060089","term_label":"molecular transducer activity","supporting_discovery_ids":[1,11,18]}],"localization":[{"term_id":"GO:0005886","term_label":"plasma membrane","supporting_discovery_ids":[3,7,34]},{"term_id":"GO:0005783","term_label":"endoplasmic reticulum","supporting_discovery_ids":[13]}],"pathway":[{"term_id":"R-HSA-112316","term_label":"Neuronal System","supporting_discovery_ids":[17,37,39]},{"term_id":"R-HSA-397014","term_label":"Muscle contraction","supporting_discovery_ids":[36]}],"complexes":["Kv1.4/Kvbeta heteromultimeric channel","Kv1.4-Kv1.1 heteromeric channel","PSD-95/Kv1.4 scaffold complex"],"partners":["DLG1","DLG2","KCNAB1","KCNAB2","DPP10","SYT1","ACTN2","KCNA1"],"other_free_text":[]}},"prefetch_data":{"uniprot":{"accession":"P22459","full_name":"Potassium voltage-gated channel subfamily A member 4","aliases":["HPCN2","Voltage-gated K(+) channel HuKII","Voltage-gated potassium channel HBK4","Voltage-gated potassium channel HK1","Voltage-gated potassium channel subunit Kv1.4"],"length_aa":653,"mass_kda":73.3,"function":"Voltage-gated potassium channel that mediates transmembrane potassium transport in excitable membranes. Forms tetrameric potassium-selective channels through which potassium ions pass in accordance with their electrochemical gradient. The channel alternates between opened and closed conformations in response to the voltage difference across the membrane (PubMed:19912772, PubMed:8495559). Can form functional homotetrameric channels and heterotetrameric channels that contain variable proportions of KCNA1, KCNA2, KCNA4, KCNA5, and possibly other family members as well; channel properties depend on the type of alpha subunits that are part of the channel (PubMed:8495559). Channel properties are modulated by cytoplasmic beta subunits that regulate the subcellular location of the alpha subunits and promote rapid inactivation. In vivo, membranes probably contain a mixture of heteromeric potassium channel complexes, making it difficult to assign currents observed in intact tissues to any particular potassium channel family member. Homotetrameric KCNA4 forms a potassium channel that opens in response to membrane depolarization, followed by rapid spontaneous channel closure (PubMed:19912772, PubMed:8495559). Likewise, a heterotetrameric channel formed by KCNA1 and KCNA4 shows rapid inactivation (PubMed:17156368)","subcellular_location":"Cell membrane; Cell projection, axon","url":"https://www.uniprot.org/uniprotkb/P22459/entry"},"depmap":{"release":"DepMap","has_data":true,"is_common_essential":false,"resolved_as":"","url":"https://depmap.org/portal/gene/KCNA4","classification":"Not Classified","n_dependent_lines":7,"n_total_lines":1208,"dependency_fraction":0.005794701986754967},"opencell":{"profiled":false,"resolved_as":"","ensg_id":"","cell_line_id":"","localizations":[],"interactors":[{"gene":"PRKACA","stoichiometry":0.2},{"gene":"TOMM20A","stoichiometry":0.2},{"gene":"VDAC1","stoichiometry":0.2},{"gene":"VDAC3","stoichiometry":0.2}],"url":"https://opencell.sf.czbiohub.org/search/KCNA4","total_profiled":1310},"omim":[{"mim_id":"619295","title":"ZDHHC PALMITOYLTRANSFERASE 14; ZDHHC14","url":"https://www.omim.org/entry/619295"},{"mim_id":"618284","title":"MICROCEPHALY, CATARACTS, IMPAIRED INTELLECTUAL DEVELOPMENT, AND DYSTONIA WITH ABNORMAL STRIATUM; MCIDDS","url":"https://www.omim.org/entry/618284"},{"mim_id":"605445","title":"DISCS LARGE-ASSOCIATED PROTEIN 1; DLGAP1","url":"https://www.omim.org/entry/605445"},{"mim_id":"604111","title":"POTASSIUM CHANNEL, VOLTAGE-GATED, SHAKER-RELATED SUBFAMILY, BETA MEMBER 3; KCNAB3","url":"https://www.omim.org/entry/604111"},{"mim_id":"603583","title":"DISCS LARGE MAGUK SCAFFOLD PROTEIN 2; DLG2","url":"https://www.omim.org/entry/603583"}],"hpa":{"profiled":true,"resolved_as":"","reliability":"","locations":[],"tissue_specificity":"Tissue enhanced","tissue_distribution":"Detected in some","driving_tissues":[{"tissue":"adrenal gland","ntpm":5.8},{"tissue":"brain","ntpm":7.9}],"url":"https://www.proteinatlas.org/search/KCNA4"},"hgnc":{"alias_symbol":["Kv1.4","HK1","HPCN2","PCN2"],"prev_symbol":["KCNA4L"]},"alphafold":{"accession":"P22459","domains":[{"cath_id":"3.30.710.10","chopping":"176-272","consensus_level":"high","plddt":94.8719,"start":176,"end":272},{"cath_id":"1.20.120.350","chopping":"287-341_368-424_438-460","consensus_level":"high","plddt":87.396,"start":287,"end":460},{"cath_id":"1.10.287.70","chopping":"466-578","consensus_level":"high","plddt":92.3428,"start":466,"end":578}],"viewer_url":"https://alphafold.ebi.ac.uk/entry/P22459","model_url":"https://alphafold.ebi.ac.uk/files/AF-P22459-F1-model_v6.cif","pae_url":"https://alphafold.ebi.ac.uk/files/AF-P22459-F1-predicted_aligned_error_v6.png","plddt_mean":69.56},"mouse_models":{"mgi_url":"https://www.informatics.jax.org/marker/summary?nomen=KCNA4","jax_strain_url":"https://www.jax.org/strain/search?query=KCNA4"},"sequence":{"accession":"P22459","fasta_url":"https://rest.uniprot.org/uniprotkb/P22459.fasta","uniprot_url":"https://www.uniprot.org/uniprotkb/P22459/entry","alphafold_viewer_url":"https://alphafold.ebi.ac.uk/entry/P22459"}},"corpus_meta":[{"pmid":"9459448","id":"PMC_9459448","title":"N-terminal palmitoylation of PSD-95 regulates association with cell membranes and interaction with K+ channel Kv1.4.","date":"1998","source":"Neuron","url":"https://pubmed.ncbi.nlm.nih.gov/9459448","citation_count":258,"is_preprint":false},{"pmid":"10884375","id":"PMC_10884375","title":"Functional consequences of elimination of i(to,f) and i(to,s): early afterdepolarizations, atrioventricular block, and ventricular arrhythmias in mice lacking Kv1.4 and expressing a dominant-negative Kv4 alpha subunit.","date":"2000","source":"Circulation research","url":"https://pubmed.ncbi.nlm.nih.gov/10884375","citation_count":140,"is_preprint":false},{"pmid":"9133364","id":"PMC_9133364","title":"Frequency-dependent inactivation of mammalian A-type K+ channel KV1.4 regulated by Ca2+/calmodulin-dependent protein kinase.","date":"1997","source":"The Journal of neuroscience : the official journal of the Society for Neuroscience","url":"https://pubmed.ncbi.nlm.nih.gov/9133364","citation_count":137,"is_preprint":false},{"pmid":"9437018","id":"PMC_9437018","title":"Presynaptic localization of Kv1.4-containing A-type potassium channels near excitatory synapses in the hippocampus.","date":"1998","source":"The Journal of neuroscience : the official journal of the Society for Neuroscience","url":"https://pubmed.ncbi.nlm.nih.gov/9437018","citation_count":112,"is_preprint":false},{"pmid":"8788936","id":"PMC_8788936","title":"C-type inactivation controls recovery in a fast inactivating cardiac K+ channel (Kv1.4) expressed in Xenopus oocytes.","date":"1995","source":"The Journal of physiology","url":"https://pubmed.ncbi.nlm.nih.gov/8788936","citation_count":102,"is_preprint":false},{"pmid":"10625685","id":"PMC_10625685","title":"Internalization of the Kv1.4 potassium channel is suppressed by clustering interactions with PSD-95.","date":"2000","source":"The Journal of biological chemistry","url":"https://pubmed.ncbi.nlm.nih.gov/10625685","citation_count":95,"is_preprint":false},{"pmid":"14688283","id":"PMC_14688283","title":"Glycosylation affects the protein stability and cell surface expression of Kv1.4 but Not Kv1.1 potassium channels. 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inactivation Ca2+-sensitive.\",\n      \"method\": \"In vitro kinase/phosphatase assays, electrophysiology (Xenopus oocyte expression), mutagenesis\",\n      \"journal\": \"The Journal of Neuroscience\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — in vitro kinase assay combined with functional electrophysiology and specific phosphatase manipulations; mechanistic claim well-supported by multiple orthogonal approaches in one study\",\n      \"pmids\": [\"9133364\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1995,\n      \"finding\": \"Deletion of the N-terminal domain (residues 2–146) of Kv1.4 removes fast N-type inactivation and reveals a slow C-type inactivation process; C-type inactivation is coupled to activation and governs the overall rate of recovery from inactivation in both full-length and N-terminal deleted channels.\",\n      \"method\": \"Two-electrode voltage clamp in Xenopus oocytes, N-terminal deletion mutagenesis, S4 voltage sensor mutation (R454Q)\",\n      \"journal\": \"The Journal of Physiology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — reconstitution in oocyte expression system with multiple deletion and point mutants; replicated across multiple constructs within same study and consistent with subsequent literature\",\n      \"pmids\": [\"8788936\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1998,\n      \"finding\": \"PSD-95 is palmitoylated on N-terminal cysteines 3 and 5, and palmitoylated PSD-95 partitions exclusively with cell membranes; palmitoylation-deficient PSD-95 mutants fail to participate in PDZ-Kv1.4 ion channel interactions in vivo.\",\n      \"method\": \"Metabolic palmitoylation labeling, mutagenesis, co-immunoprecipitation, cell-surface distribution assays\",\n      \"journal\": \"Neuron\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1–2 / Strong — metabolic labeling plus mutagenesis plus functional co-IP; multiple orthogonal methods in one study, highly cited\",\n      \"pmids\": [\"9459448\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2000,\n      \"finding\": \"PSD-95 clustering completely suppresses Kv1.4 internalization in HEK293 cells; a palmitoylation-competent but clustering-deficient PSD-95 mutant (C35S) instead enhances the rate of Kv1.4 internalization, demonstrating that PSD-95-mediated clustering—not mere binding—stabilizes Kv1.4 at the cell surface.\",\n      \"method\": \"Cell-surface biotinylation internalization assay, immunochemistry, whole-cell electrophysiology, GFP-tagged Kv1.4 imaging\",\n      \"journal\": \"The Journal of Biological Chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — multiple orthogonal methods (biotinylation kinetics, imaging, electrophysiology) in single study with rigorous mutant controls\",\n      \"pmids\": [\"10625685\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2003,\n      \"finding\": \"PSD-95 palmitoylation recruits Kv1.4 (but not Kv4.2) into lipid rafts via the Kv1.4 C-terminal PDZ-binding motif; deleting this motif or substituting a palmitoylation-deficient PSD-95 eliminates raft recruitment.\",\n      \"method\": \"Lipid raft fractionation, raft patching/immunostaining, co-expression in heterologous system, deletion mutagenesis\",\n      \"journal\": \"The Journal of Biological Chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — reciprocal fractionation plus imaging plus mutagenesis; multiple orthogonal approaches establishing mechanism\",\n      \"pmids\": [\"14559911\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1999,\n      \"finding\": \"N-terminal cysteines 3 and 5 of PSD-95 are required for PSD-95 multimerization and formation of a ternary complex with Kv1.4 and Fasciclin II, but are dispensable for membrane association and binary Kv1.4 binding; multimerization is required for simultaneous binding of multiple membrane protein ligands.\",\n      \"method\": \"Co-immunoprecipitation, cell clustering assays, mutagenesis\",\n      \"journal\": \"The Journal of Biological Chemistry\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — co-IP with mutagenesis, single lab, two orthogonal readouts\",\n      \"pmids\": [\"9867876\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2001,\n      \"finding\": \"PDZ2 of PSD-95 (highest affinity for Kv1.4) is the primary domain required for efficient Kv1.4 clustering; functional PDZ2 must occupy the second position in the full-length protein, as inversion of PDZ1-PDZ2 order abolishes clustering activity.\",\n      \"method\": \"PDZ domain missense/deletion mutagenesis, co-expression clustering assay in COS-1 cells\",\n      \"journal\": \"The Journal of Biological Chemistry\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — structure-function with multiple PDZ mutants in heterologous cells, single lab\",\n      \"pmids\": [\"11723117\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2003,\n      \"finding\": \"N-glycosylation of Kv1.4 (attached at the S1-S2 linker) promotes protein stability and cell-surface expression; preventing glycosylation decreases protein stability and causes intracellular retention, with effects contingent on a pore region trafficking determinant that can be transferred to chimeric Kv1.1.\",\n      \"method\": \"N-glycosylation mutagenesis, cell-surface expression assays, chimeric channel construction in transfected cells\",\n      \"journal\": \"The Journal of Biological Chemistry\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — mutagenesis combined with chimera trafficking assays, single lab, multiple constructs\",\n      \"pmids\": [\"14688283\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2003,\n      \"finding\": \"Kv1.4 cell-surface trafficking requires interdependence between a pore region determinant and the cytoplasmic C-terminal VXXSL motif; removal of VXXSL only inhibits surface expression when the Kv1.4 pore (specifically a threonine in the deep pore) is present, not when replaced by the Kv1.1 pore.\",\n      \"method\": \"Chimeric channel mutagenesis, cell-surface expression assays in transfected cells\",\n      \"journal\": \"The Biochemical Journal\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — systematic chimeric and point-mutant trafficking analysis, single lab\",\n      \"pmids\": [\"12901718\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2001,\n      \"finding\": \"The N-terminus of Kv1.4 interacts with the spectrin repeats of alpha-actinin-2 (but Kv1.1, 1.2, 1.3 do not); the Kv1.4/Kv1.5 binding region in alpha-actinin-2 lies within its internal spectrin repeats, and calmodulin has no effect on this interaction.\",\n      \"method\": \"Yeast two-hybrid, in vitro binding (pull-down) assays, deletion mutagenesis\",\n      \"journal\": \"FEBS Letters\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — yeast two-hybrid plus in vitro pull-down, two orthogonal methods, single lab\",\n      \"pmids\": [\"11389904\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2000,\n      \"finding\": \"Acidosis inhibits Kv1.4 during repetitive pulsing by protonation of extracellular histidine H508, which enhances C-type inactivation and slows recovery from N-type inactivation; deletion of both N-terminal inactivation ball domains greatly reduces the acidosis effect, and raising extracellular K+ or the K532Y mutation abolishes it.\",\n      \"method\": \"Two-electrode voltage clamp in Xenopus oocytes, site-directed mutagenesis (H508Q, K532Y), extracellular K+ manipulation\",\n      \"journal\": \"The Journal of Physiology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — mutagenesis of specific residues combined with multiple pharmacological manipulations in oocyte system, mechanistically conclusive\",\n      \"pmids\": [\"10896716\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2002,\n      \"finding\": \"C-type inactivation of Kv1.4 is regulated by extracellular K+ (via pore mouth and intracellular K+ binding sites), intracellular K+ concentration, extracellular pH via H508 in the S5-H5 linker, and an extracellular K532Y mutation; an intracellular V561A mutation in S6 alters C-type inactivation and inverts its relationship with extracellular K+, suggesting transmembrane communication between intracellular and extracellular pore regions.\",\n      \"method\": \"Two-electrode voltage clamp in Xenopus oocytes, N-terminal deletion, site-directed mutagenesis (H508, K532, V561A), ionic substitution\",\n      \"journal\": \"American Journal of Physiology – Heart and Circulatory Physiology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — systematic mutagenesis of multiple key residues combined with ionic manipulations, mechanistically rigorous single-lab study\",\n      \"pmids\": [\"12388308\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1995,\n      \"finding\": \"Kv beta 3 co-expressed with Kv1.4 accelerates both the fast and slow components of inactivation, increases the contribution of the slow component, slows recovery from inactivation (in full-length but not N-terminal deleted Kv1.4), and slows deactivation, without strongly affecting activation voltage dependence.\",\n      \"method\": \"Two-electrode voltage clamp in Xenopus oocytes, co-expression of alpha and beta subunits\",\n      \"journal\": \"The American Journal of Physiology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — functional co-expression assay with deletion mutant controls, single lab\",\n      \"pmids\": [\"7631872\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1997,\n      \"finding\": \"Truncated Kv1.1 polypeptide (Kv1.1N206Tag) forms heteromultimeric complexes with native Kv1.4 (and Kv1.5) in GH3 cells, retaining these complexes in the endoplasmic reticulum and preventing their trafficking to the plasma membrane, thereby acting as a dominant-negative suppressor.\",\n      \"method\": \"Double immunoprecipitation, [35S]methionine pulse-chase, subcellular fractionation, immunofluorescence confocal microscopy\",\n      \"journal\": \"The Journal of Biological Chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — reciprocal double immunoprecipitation plus fractionation plus confocal localization, multiple orthogonal methods\",\n      \"pmids\": [\"9334228\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1998,\n      \"finding\": \"Kvbeta1.2 N-terminus (beta-ball) directly blocks both Kv1.4 and N-terminal-deleted Kv1.4; Kvbeta1-C (C-terminus alone) and Kvbeta2 enhance N-type inactivation of Kv1.4 allosterically without direct ball domain involvement; alpha-beta interaction is restricted to the N-terminus of Kv1.4 and the C-terminus of Kvbeta.\",\n      \"method\": \"Two-electrode voltage clamp in Xenopus oocytes, yeast two-hybrid, deletion mutants\",\n      \"journal\": \"The Journal of Physiology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — yeast two-hybrid plus functional oocyte electrophysiology, single lab\",\n      \"pmids\": [\"9763623\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1997,\n      \"finding\": \"Kvbeta1.1 and Kvbeta2.1 both accelerate the activation time constant of Kv1.4 without altering voltage dependence of activation or steady-state inactivation; Kvbeta2.1, which lacks an N-terminal inactivation domain, is nearly as effective as Kvbeta1.1 at speeding activation.\",\n      \"method\": \"Two-electrode voltage clamp in Xenopus oocytes, co-expression\",\n      \"journal\": \"Pflügers Archiv\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Weak — functional co-expression with quantitative kinetics, single lab, single method\",\n      \"pmids\": [\"9359902\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2001,\n      \"finding\": \"Kvbeta2 NADPH-binding and putative catalytic site mutations do not disrupt Kvbeta2–Kv1.4 physical interaction (confirmed by yeast two-hybrid) but abolish the expression-enhancing effect of Kvbeta2 on Kv1.4 surface protein and current amplitude without affecting the rate of inactivation increase, suggesting NADPH binding/oxidoreductase activity mediates Kv1.4 processing/trafficking separately from inactivation modulation.\",\n      \"method\": \"Yeast two-hybrid, Xenopus oocyte co-expression, Western blot, site-directed mutagenesis\",\n      \"journal\": \"The Journal of Biological Chemistry\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — yeast two-hybrid plus functional electrophysiology plus Western blot, multiple methods, single lab\",\n      \"pmids\": [\"11024060\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1998,\n      \"finding\": \"Kv1.4 immunoreactivity in hippocampus is concentrated presynaptically on axons and axonal necks near excitatory synaptic boutons (mossy fiber and perforant path terminals), as established by confocal immunofluorescence and ultrastructural immunoelectron microscopy.\",\n      \"method\": \"Confocal immunofluorescence microscopy, ultrastructural immunoelectron microscopy\",\n      \"journal\": \"The Journal of Neuroscience\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — dual ultrastructural and confocal immunolabeling establishing presynaptic axonal localization, single lab\",\n      \"pmids\": [\"9437018\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1996,\n      \"finding\": \"N-type inactivation of Kv1.4 is mediated by the proximal N-terminal ball domain; a single inactivating Kv1.4 subunit confers inactivation on heteromultimers with non-inactivating Kv1.5, and rate of inactivation is indistinguishable in channels with one versus two inactivating subunits.\",\n      \"method\": \"Two-electrode voltage clamp in Xenopus oocytes, Kv1.4-Kv1.5 tandem fusion constructs, N-terminal deletion mutants\",\n      \"journal\": \"The Journal of Membrane Biology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — reconstituted heteromultimers with tandem constructs and deletions, single lab\",\n      \"pmids\": [\"8661510\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1996,\n      \"finding\": \"Oxidation of N-terminal cysteine residues by cysteine-modifying reagents (DTBNP, chloramine-T) removes Kv1.4 inactivation and slows deactivation; these effects are reversed by the reducing agent DTT, indicating redox state controls Kv1.4 gating.\",\n      \"method\": \"Whole-cell patch clamp in HEK-293 cells, cysteine-specific oxidizing and reducing agents\",\n      \"journal\": \"Pflügers Archiv\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — pharmacological manipulation with reversibility controls, single lab, single method\",\n      \"pmids\": [\"8584439\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2001,\n      \"finding\": \"Riluzole irreversibly slows Kv1.4 inactivation by an oxidative, voltage-dependent mechanism involving a cysteine in the N-terminal inactivation domain; this effect is abolished by reducing agents (DTT, glutathione) in the pipette and does not occur when applied at depolarized holding potentials (where the N-terminal is in the inactivated position), indicating the accessible cysteine is protected in the inactivated state.\",\n      \"method\": \"Whole-cell patch clamp in bovine adrenal zona fasciculata cells, pharmacological manipulation with antioxidants and nucleotide analogs\",\n      \"journal\": \"The Journal of Pharmacology and Experimental Therapeutics\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — native channel electrophysiology with multiple pharmacological controls, single lab\",\n      \"pmids\": [\"11561084\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2003,\n      \"finding\": \"Quinidine blocks Kv1.4 through open channel block and subsequently promotes C-type inactivation by a voltage-dependent allosteric conformational change; interventions that prevent C-type inactivation (elevated extracellular K+ or K532Y mutation) abolish the time-dependent quinidine effect, and the V561A S6 mutation reduces channel affinity for both quinidine and the N-terminal domain.\",\n      \"method\": \"Two-electrode voltage clamp in Xenopus oocytes, site-directed mutagenesis (K532Y, V561A), extracellular K+ manipulation, mathematical modeling\",\n      \"journal\": \"The Journal of Physiology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — systematic mutagenesis of inactivation-related residues combined with ionic and pharmacological manipulations, with quantitative modeling\",\n      \"pmids\": [\"12527726\", \"14608006\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2006,\n      \"finding\": \"DPP10 (a dipeptidyl peptidase-related ancillary subunit) co-expressed with Kv1.4 accelerates time to peak current and shifts the half-inactivation potential of steady-state activation and inactivation to more negative values, but slows recovery from inactivation, demonstrating DPP10 as a modulator of Kv1.4 inactivation.\",\n      \"method\": \"Xenopus oocyte co-expression electrophysiology, DPP10 truncation mutants\",\n      \"journal\": \"American Journal of Physiology – Cell Physiology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — functional co-expression with truncation mutant controls, single lab\",\n      \"pmids\": [\"16738002\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2006,\n      \"finding\": \"EA1 mutations (E325D, V404I, V408A, I177N) in Kv1.1 reduce the rate and degree of N-type inactivation and accelerate recovery from fast inactivation in heteromeric Kv1.4-Kv1.1/Kvbeta1.x channels; Kvbeta1.1 and Kvbeta1.2 modulate Kv1.4-1.1 channels by increasing N-type inactivation rate, slowing recovery, and accelerating cumulative inactivation.\",\n      \"method\": \"Two-electrode voltage clamp in Xenopus oocytes, tandem-linked Kv1.4-Kv1.1 constructs, co-expression with Kvbeta subunits\",\n      \"journal\": \"The European Journal of Neuroscience\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — heteromeric channel functional analysis with multiple mutations, single lab\",\n      \"pmids\": [\"17156368\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2006,\n      \"finding\": \"EA1 mutation F184C in Kv1.1 increases Zn2+ sensitivity of heteromeric Kv1.4-Kv1.1/Kvbeta1.1 channels; Zn2+ occupies a high-affinity and a low-affinity site in this heteromeric complex, slowing activation, increasing time to peak current, decreasing N-type inactivation rate and amount, and slowing repriming.\",\n      \"method\": \"Two-electrode voltage clamp in Xenopus oocytes, Zn2+ dose-response analysis, EA1 point mutant\",\n      \"journal\": \"American Journal of Physiology – Cell Physiology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — concentration-response and kinetic analysis of heteromeric channels with mutation, single lab\",\n      \"pmids\": [\"16956965\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2005,\n      \"finding\": \"Ser229 in the T1 domain of Kv1.4 is phosphorylated by PKA in cultured rat cortical neurons; neuronal transmission stimuli (glutamate, high K+, K+ channel blockers) stimulate this phosphorylation via NMDA receptor-mediated Ca2+ influx, while tetrodotoxin and Ca2+ depletion inhibit it; S229A mutation increases Kv1.4 current density.\",\n      \"method\": \"In vitro protein kinase assay, phospho-specific antibody Western blot, site-directed mutagenesis, pharmacological dissection\",\n      \"journal\": \"Journal of Neurochemistry\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 1–2 / Moderate — in vitro kinase assay plus phospho-Western plus mutagenesis functional assay, single lab\",\n      \"pmids\": [\"16000151\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2003,\n      \"finding\": \"Arachidonic acid and cis-polyunsaturated fatty acids directly inhibit Kv1.4 current and accelerate inactivation kinetics in bovine adrenal zona fasciculata cells; this inhibition is kinetically distinct from TREK-1 activation and does not require formation of AA metabolites (ETYA also inhibits Kv1.4).\",\n      \"method\": \"Whole-cell patch clamp on native cells, pharmacological manipulation with fatty acid analogs and pathway inhibitors\",\n      \"journal\": \"The Journal of Membrane Biology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — native cell electrophysiology with metabolic pathway controls, single lab\",\n      \"pmids\": [\"14724761\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2003,\n      \"finding\": \"Endothelin-1 acting via ETA receptor decreases Kv1.4 transient outward current by ~85% in Xenopus oocytes; mutagenesis identified two phosphorylation sites (PKC and CaMKII) in the Kv1.4 sequence responsible for ET-1-mediated suppression.\",\n      \"method\": \"Xenopus oocyte co-expression electrophysiology, ETA receptor co-expression, site-directed mutagenesis of phosphorylation sites\",\n      \"journal\": \"Biochemical and Biophysical Research Communications\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — functional co-expression with receptor and channel mutagenesis, single lab\",\n      \"pmids\": [\"14521958\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2011,\n      \"finding\": \"Position-dependent attenuation of Kv1.4 N-type inactivation by the Kv1.6 NIP domain requires Kv1.4 and Kv1.6 to be adjacent subunits in the tetramer; when separated by one Kv1.2 subunit, fast inactivation is restored; mutation of critical glutamates within the NIP abolishes suppression of inactivation.\",\n      \"method\": \"Gene concatenation to form single-chain heterotetramers expressed in HEK293 cells, whole-cell electrophysiology, NIP mutagenesis\",\n      \"journal\": \"The Biochemical Journal\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — defined heterotetramers with programmed subunit positions plus mutagenesis, rigorous structure-function study\",\n      \"pmids\": [\"21352098\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2014,\n      \"finding\": \"Synaptotagmin I directly interacts with the N-terminus of Kv1.4 (independent of other synaptic proteins) and delays Kv1.4 N-type fast inactivation in a Ca2+-dependent manner, as shown by Co-IP and patch-clamp in HEK293T cells.\",\n      \"method\": \"Co-immunoprecipitation, whole-cell patch clamp in HEK293T cells, mutagenesis of Kv1.4 N-terminus\",\n      \"journal\": \"Molecular Brain\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — co-IP plus functional electrophysiology with mutagenesis, single lab\",\n      \"pmids\": [\"24423395\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2010,\n      \"finding\": \"Electrostatic interaction between the positively charged (residues 83–98) and negatively charged (residues 123–137) segments of the Kv1.4 N-terminus accelerates N-type inactivation; neutralization or deletion of the positive segment, or making both segments the same charge, slows inactivation without altering voltage dependence of activation.\",\n      \"method\": \"Whole-cell patch clamp, site-directed and deletion mutagenesis of N-terminal charged segments\",\n      \"journal\": \"Biochimica et Biophysica Acta\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — mutagenesis of multiple residues with functional electrophysiology, single lab\",\n      \"pmids\": [\"20674541\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2007,\n      \"finding\": \"Ginsenoside Rg3 inhibits Kv1.4 current by interacting with the extracellular Lys531 residue (part of the K+ activation and TEA binding site); K531Y mutation abolishes Rg3 inhibition and makes the channel sensitive to external TEA; elevated external K+ also reduces Rg3 inhibition, and Rg3 promotes C-type inactivation via this residue.\",\n      \"method\": \"Xenopus oocyte two-electrode voltage clamp, site-directed mutagenesis (K531Y and others), docking modeling\",\n      \"journal\": \"Molecular Pharmacology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — mutagenesis plus pharmacological manipulations plus computational docking, single lab\",\n      \"pmids\": [\"17959711\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2016,\n      \"finding\": \"A missense variant p.Arg89Gln in KCNA4 causes severe loss-of-function of Kv1.4 channels (significantly reduced current amplitude); co-expression of WT and R89Q mRNA in Xenopus oocytes confirms dominant-negative-like reduction in current, and KCNA4 interacts with synaptotagmin I, DLG1, and DLG2.\",\n      \"method\": \"Two-electrode voltage clamp in Xenopus oocytes, whole-exome sequencing, RT-PCR, co-immunoprecipitation/interaction assays\",\n      \"journal\": \"Journal of Medical Genetics\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — functional expression with disease mutant and interaction data, single study, multiple methods\",\n      \"pmids\": [\"27582084\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"Nucleoporin 50 (Nup50) directly binds the Kcna4 promoter region via its FG-repeat domain and activates Kcna4 transcription and translation; Nup50 overexpression increases Ito,s currents in cardiomyocytes and knockdown reduces them.\",\n      \"method\": \"Luciferase reporter assay, chromatin immunoprecipitation, immunofluorescence, whole-cell patch clamp in cardiomyocytes\",\n      \"journal\": \"Journal of Cell Science\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — ChIP plus reporter plus functional electrophysiology, single lab\",\n      \"pmids\": [\"34409458\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2017,\n      \"finding\": \"PKC and AMPK activation reduce Kv1.4 cell-surface expression and current levels; PI3K, SGK1, Nedd4-1, and Nedd4-2 do not affect Kv1.4 surface localization, distinguishing Kv1.4 trafficking regulation from related Kv channels.\",\n      \"method\": \"Confocal microscopy in MDCK cells, two-electrode voltage clamp in Xenopus oocytes, pharmacological kinase activation\",\n      \"journal\": \"Channels\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — imaging plus electrophysiology in two systems, single lab, pharmacological approach\",\n      \"pmids\": [\"29168928\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2023,\n      \"finding\": \"miR-448 directly binds the 3'-UTR of KCNA4 mRNA and reduces KCNA4 expression and Ito current; inhibition of miR-448 restores KCNA4 levels, establishing a post-transcriptional regulatory mechanism for Kv1.4 downregulation in ischemia.\",\n      \"method\": \"RNA pull-down assay, miR-448 decoy and binding site mutation, qRT-PCR, electrophysiology\",\n      \"journal\": \"Heart Rhythm\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — pull-down assay with binding site mutation and functional current rescue, single lab\",\n      \"pmids\": [\"36693615\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2000,\n      \"finding\": \"Kv1.4-encoded slow transient outward current (Ito,s) is eliminated in Kv1.4 knockout mice; upregulation of Kv1.4 in ventricular myocytes of Kv4.2W362F-expressing mice underlies the appearance of slow Ito in those cells; double knockout/transgenic mice (Kv4.2W362F×Kv1.4−/−) lack both Ito,f and Ito,s, develop early afterdepolarizations, AV block, and ventricular tachycardia.\",\n      \"method\": \"Targeted gene knockout, transgenic mouse models, in vivo telemetric ECG, patch clamp of isolated myocytes\",\n      \"journal\": \"Circulation Research\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — genetic loss-of-function (KO mice) combined with in vivo electrophysiology and cellular recordings, multiple orthogonal readouts\",\n      \"pmids\": [\"10884375\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1998,\n      \"finding\": \"Knockdown of Kv1.4 by antisense oligonucleotides in rat hippocampus eliminates both early- and late-phase LTP and reduces paired-pulse facilitation (a presynaptic effect) in CA1 pyramidal neurons without affecting spatial memory or dentate gyrus LTP.\",\n      \"method\": \"Intraventricular antisense oligonucleotide injection, RT-PCR, Western blot, hippocampal slice electrophysiology, behavioral maze testing\",\n      \"journal\": \"PNAS\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — antisense knockdown confirmed by protein Western blot and functional LTP assays, single lab\",\n      \"pmids\": [\"9844011\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"A de novo missense variant Kv1.4-V558L (located in the S6 hinge/selectivity filter) causes severe loss-of-function in a cell-based patch-clamp system without significantly affecting channel trafficking or plasma membrane localization, associated with early-onset developmental epileptic encephalopathy.\",\n      \"method\": \"Whole-exome sequencing trio, patch-clamp in cell-based system, trafficking/localization assay\",\n      \"journal\": \"Human Molecular Genetics\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — functional electrophysiology with localization assay, single study, single lab\",\n      \"pmids\": [\"40472070\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2023,\n      \"finding\": \"Tyramine acting via TAAR1 receptor reduces Kv1.4-mediated IA in trigeminal ganglion neurons through a Gβγ-dependent PKCθ signaling cascade; siRNA knockdown of Kv1.4 abolishes TAAR1-induced IA decrease and pain hypersensitivity, while lentiviral Kv1.4 overexpression occludes TAAR1 blockade analgesia.\",\n      \"method\": \"Whole-cell patch clamp, siRNA knockdown, lentiviral overexpression, PKC isoform inhibition, Gβγ inhibition, mouse behavioral pain assays\",\n      \"journal\": \"The Journal of Headache and Pain\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — multiple genetic and pharmacological interventions with behavioral readout, single lab\",\n      \"pmids\": [\"37158881\"],\n      \"is_preprint\": false\n    }\n  ],\n  \"current_model\": \"Kv1.4 (KCNA4) is a voltage-gated, rapidly-inactivating A-type potassium channel that undergoes N-type inactivation via a ball-and-chain mechanism (N-terminal inactivation domain) and slower C-type inactivation regulated by extracellular residues H508 and K532, intracellular S6 residue V561, and permeant K+ ions; its inactivation kinetics are modulated by CaMKII phosphorylation of an N-terminal residue and by PKA-mediated phosphorylation of Ser229, by redox state of N-terminal cysteines, by interacting beta-subunits (Kvbeta1.1, Kvbeta1.2, Kvbeta2, Kvbeta3) and the ancillary subunit DPP10, and by synaptotagmin I; cell-surface expression is governed by N-glycosylation, a pore-region trafficking determinant, a C-terminal VXXSL motif, PKC and AMPK signaling, and stabilization by PSD-95 clustering (which also recruits Kv1.4 into palmitoylation-dependent lipid rafts and suppresses internalization); presynaptically localized at excitatory hippocampal synapses, Kv1.4 is required for slow Ito,s in heart and contributes to IA in cortical neurons, bladder and trigeminal afferents, and SCN circadian pacemaking, with loss-of-function causing arrhythmias, neuronal hyperexcitability, and in humans, epileptic encephalopathy and a syndrome of striatal thinning, congenital cataract, and intellectual disability.\"\n}\n```","stage2_raw":"{\n  \"mechanistic_narrative\": \"KCNA4 encodes Kv1.4, a voltage-gated, rapidly-inactivating A-type potassium channel that shapes membrane excitability in heart and nervous system by generating a slow transient outward current (Ito,s in cardiomyocytes) and A-type currents (IA) in neurons [#36, #39]. Its hallmark fast N-type inactivation is conferred by a proximal N-terminal ball domain, where an electrostatic interaction between positively and negatively charged segments tunes inactivation rate; a single inactivating subunit suffices to inactivate a heteromultimer [#18, #30, #1]. Removal of this N-terminal domain unmasks a slower C-type inactivation coupled to activation and governed by pore residues—extracellular H508 and K532/K531 and the S6 residue V561—and by permeant K+ ions, with extracellular acidosis enhancing C-type inactivation through protonation of H508 [#1, #10, #11]. Channel gating is dynamically regulated: CaMKII and PKA (at Ser229 in the T1 domain) phosphorylation, redox modification of N-terminal cysteines, fatty acids, and accessory subunits (Kvbeta1.1/1.2/2/3, DPP10) and synaptotagmin I all modulate inactivation and recovery kinetics [#0, #25, #19, #26, #12, #14, #22, #29]. Surface expression and stability depend on N-glycosylation, a pore trafficking determinant interdependent with the C-terminal VXXSL motif, PKC/AMPK signaling, and clustering by PSD-95, which suppresses internalization and recruits Kv1.4 into palmitoylation-dependent lipid rafts via its C-terminal PDZ-binding motif [#7, #8, #34, #3, #4]. Kv1.4 localizes presynaptically at excitatory hippocampal synapses and is required for hippocampal LTP, and its loss in mice eliminates Ito,s and predisposes to arrhythmias including ventricular tachycardia [#17, #37, #36]. In humans, loss-of-function KCNA4 missense variants (p.Arg89Gln; p.Val558L in the S6 hinge) cause severe channel dysfunction associated with developmental epileptic encephalopathy [#32, #38].\",\n  \"teleology\": [\n    {\n      \"year\": 1995,\n      \"claim\": \"Establishing the two-component inactivation architecture of Kv1.4 separated the fast N-type 'ball' mechanism from a slower intrinsic C-type process and showed C-type inactivation sets the overall recovery rate.\",\n      \"evidence\": \"N-terminal deletion and S4 mutagenesis with two-electrode voltage clamp in Xenopus oocytes\",\n      \"pmids\": [\"8788936\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Structural basis of C-type inactivation not resolved\", \"Coupling to activation defined functionally, not structurally\"]\n    },\n    {\n      \"year\": 1996,\n      \"claim\": \"Identifying the proximal N-terminal ball domain and the redox sensitivity of N-terminal cysteines defined the molecular determinant of fast inactivation and its chemical regulation.\",\n      \"evidence\": \"Tandem Kv1.4-Kv1.5 fusion/deletion constructs and cysteine-modifying reagents with voltage/patch clamp\",\n      \"pmids\": [\"8661510\", \"8584439\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Stoichiometry of redox effect on tetramer not quantified\", \"Physiological oxidant in vivo not identified\"]\n    },\n    {\n      \"year\": 1997,\n      \"claim\": \"Phosphoregulation made Kv1.4 inactivation Ca2+-responsive, linking CaMKII/calcineurin signaling to channel gating and use-dependent availability.\",\n      \"evidence\": \"In vitro kinase/phosphatase assays plus oocyte electrophysiology and mutagenesis\",\n      \"pmids\": [\"9133364\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Precise N-terminal phosphoresidue partially defined\", \"Native neuronal/cardiac relevance not directly tested here\"]\n    },\n    {\n      \"year\": 1997,\n      \"claim\": \"Beta-subunit and dominant-negative truncation studies established that Kv1.4 assembles into heteromultimers whose assembly state controls both gating and ER export.\",\n      \"evidence\": \"Co-expression electrophysiology and double immunoprecipitation/fractionation in GH3 cells\",\n      \"pmids\": [\"9359902\", \"9334228\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Native subunit composition not enumerated\", \"Trafficking checkpoint mechanism not molecularly defined\"]\n    },\n    {\n      \"year\": 1998,\n      \"claim\": \"Defining the PSD-95 palmitoylation-PDZ axis and presynaptic localization placed Kv1.4 within scaffolded synaptic membrane microdomains and a functional LTP role.\",\n      \"evidence\": \"Palmitoylation labeling, co-IP, immuno-EM localization, and hippocampal antisense knockdown with slice electrophysiology\",\n      \"pmids\": [\"9459448\", \"9437018\", \"9844011\", \"9763623\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Direct presynaptic current contribution not isolated\", \"Causal chain from channel loss to LTP deficit not fully resolved\"]\n    },\n    {\n      \"year\": 2000,\n      \"claim\": \"Demonstrating PSD-95 clustering suppresses internalization and that acidosis enhances C-type inactivation via H508 connected scaffolding and pore chemistry to channel surface stability and pathophysiological modulation.\",\n      \"evidence\": \"Biotinylation internalization assays in HEK293 and site-directed mutagenesis (H508Q, K532Y) with oocyte voltage clamp\",\n      \"pmids\": [\"10625685\", \"10896716\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Internalization endocytic machinery not identified\", \"In vivo significance of acidosis effect not tested\"]\n    },\n    {\n      \"year\": 2000,\n      \"claim\": \"Knockout and transgenic mouse models proved Kv1.4 is the molecular basis of cardiac Ito,s and that its loss combined with Ito,f deficiency produces lethal arrhythmias.\",\n      \"evidence\": \"Gene knockout/transgenic mice with in vivo ECG and myocyte patch clamp\",\n      \"pmids\": [\"10884375\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Compensatory channel remodeling not fully mapped\", \"Human cardiac translation indirect\"]\n    },\n    {\n      \"year\": 2003,\n      \"claim\": \"Defining glycosylation, pore-region, and VXXSL trafficking determinants, plus lipid-raft recruitment, established the structural code controlling Kv1.4 surface expression.\",\n      \"evidence\": \"Chimeric and glycosylation mutagenesis, surface expression assays, and lipid raft fractionation in heterologous cells\",\n      \"pmids\": [\"14688283\", \"12901718\", \"14559911\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Trafficking machinery and chaperones not identified\", \"Interdependence mechanism between pore and C-terminus not structurally resolved\"]\n    },\n    {\n      \"year\": 2005,\n      \"claim\": \"Identifying PKA phosphorylation of T1-domain Ser229 driven by NMDA-receptor Ca2+ influx linked synaptic activity to Kv1.4 current density in native neurons.\",\n      \"evidence\": \"In vitro kinase assay, phospho-specific Western blot, and S229A mutagenesis in cortical neurons\",\n      \"pmids\": [\"16000151\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Mechanism by which Ser229 phosphorylation alters current density unclear\", \"Single lab\"]\n    },\n    {\n      \"year\": 2011,\n      \"claim\": \"Programmed heterotetramer studies showed positional, subunit-adjacency requirements for inactivation modulation, refining the structural logic of heteromeric Kv1.4 channels.\",\n      \"evidence\": \"Single-chain concatenated heterotetramers in HEK293 with NIP mutagenesis and whole-cell electrophysiology\",\n      \"pmids\": [\"21352098\", \"16738002\", \"20674541\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Native tetramer subunit arrangement unknown\", \"Generality across other Kv1.x partners not established\"]\n    },\n    {\n      \"year\": 2014,\n      \"claim\": \"Identifying direct synaptotagmin I binding to the Kv1.4 N-terminus added a Ca2+-dependent presynaptic regulator of fast inactivation.\",\n      \"evidence\": \"Co-IP and whole-cell patch clamp with N-terminal mutagenesis in HEK293T\",\n      \"pmids\": [\"24423395\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Single Co-IP system without reciprocal in vivo validation\", \"Physiological synaptic consequence not measured\"]\n    },\n    {\n      \"year\": 2021,\n      \"claim\": \"Transcriptional and post-transcriptional regulators (Nup50, miR-448) and trafficking kinases (PKC, AMPK) were shown to set Kv1.4 abundance and current, expanding regulation beyond gating.\",\n      \"evidence\": \"ChIP/reporter assays, RNA pull-down with binding-site mutation, and kinase activation with imaging/electrophysiology\",\n      \"pmids\": [\"34409458\", \"36693615\", \"29168928\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Disease contexts inferred (ischemia) not fully tested in vivo\", \"Integration of these inputs with channel function incomplete\"]\n    },\n    {\n      \"year\": 2025,\n      \"claim\": \"Human genetic and functional studies established KCNA4 loss-of-function variants as causes of developmental epileptic encephalopathy, providing direct disease relevance.\",\n      \"evidence\": \"Trio whole-exome sequencing with cell-based patch clamp and trafficking assays (p.Arg89Gln, p.Val558L)\",\n      \"pmids\": [\"27582084\", \"40472070\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Genotype-phenotype spectrum not delineated\", \"Mechanism linking channel loss to encephalopathy circuit defects unknown\"]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"How the diverse regulatory inputs—phosphorylation, redox, lipid, scaffolding, accessory subunits, and transcriptional control—are integrated in native presynaptic and cardiac contexts, and how loss-of-function produces specific human neurodevelopmental phenotypes, remains unresolved.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"No structural model of full regulated channel complex\", \"Native cell-type-specific regulatory hierarchy undefined\", \"Disease mechanism at circuit level uncharacterized\"]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0005215\", \"supporting_discovery_ids\": [1, 36, 39]},\n      {\"term_id\": \"GO:0005216\", \"supporting_discovery_ids\": [1, 18]},\n      {\"term_id\": \"GO:0060089\", \"supporting_discovery_ids\": [1, 11, 18]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005886\", \"supporting_discovery_ids\": [3, 7, 34]},\n      {\"term_id\": \"GO:0005783\", \"supporting_discovery_ids\": [13]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"R-HSA-112316\", \"supporting_discovery_ids\": [17, 37, 39]},\n      {\"term_id\": \"R-HSA-397014\", \"supporting_discovery_ids\": [36]}\n    ],\n    \"complexes\": [\n      \"Kv1.4/Kvbeta heteromultimeric channel\",\n      \"Kv1.4-Kv1.1 heteromeric channel\",\n      \"PSD-95/Kv1.4 scaffold complex\"\n    ],\n    \"partners\": [\n      \"DLG1\",\n      \"DLG2\",\n      \"KCNAB1\",\n      \"KCNAB2\",\n      \"DPP10\",\n      \"SYT1\",\n      \"ACTN2\",\n      \"KCNA1\"\n    ],\n    \"other_free_text\": []\n  }\n}","audit_flag":null,"evaluation":{"pairwise":"win","faith_supported":7,"faith_total":7,"faith_pct":100.0}}