Affinage

KCNJ9

G protein-activated inward rectifier potassium channel 3 · UniProt Q92806

Length
393 aa
Mass
44.0 kDa
Annotated
2026-06-10
20 papers in source corpus 13 papers cited in narrative 13 extracted findings
Cross-family judge vs UniProt: Affinage preferred faithfulness: 5/5 claims corpus-supported (100%)

Mechanistic narrative

Synthesis pass · prose summary of the discoveries below

KCNJ9/GIRK3 (Kir3.3) is a pore-forming subunit of G-protein-gated inwardly rectifying K+ (GIRK) channels that co-assembles with GIRK1 or GIRK2 into functional heteromultimeric channels gated by Gβγ, with GIRK2/GIRK3 channels showing markedly lower Gβγ sensitivity than GIRK1-containing channels (PMID:10341034, PMID:10956667). In neurons, GIRK2/GIRK3-containing channels mediate the acute opioid-induced hyperpolarization of locus ceruleus neurons, accounting for the bulk of the opioid-sensitive K+ current (PMID:12040038), and GIRK3 sits in a shared pathway downstream of opioid, α2-adrenergic, and cannabinoid receptors that produces analgesia (PMID:18300945). GIRK3 assembles into stable receptor-channel complexes with GABA-B receptors as GIRK1/GIRK3 heterotetramers, likely forming early in the secretory pathway (PMID:20846323), and its C-terminal intracellular domain directly binds NCAM and TrkB, the latter regulating GIRK3 plasma-membrane expression (PMID:20610389). Through these channels GIRK3 shapes addiction-relevant circuitry: it gates the mesolimbic dopaminergic response to ethanol in the VTA (PMID:25964320), is required for methamphetamine-induced plasticity of GABA-B/GIRK signaling (PMID:26985023), and contributes to sedative-hypnotic withdrawal severity (PMID:19759313). Beyond the nervous system, GIRK3 acts in non-excitable skeletal cells, restraining endochondral bone formation downstream of kappa-opioid receptor signaling in chondrocytes (PMID:35314385) and limiting bone mass in osteoblasts/osteocytes through modulation of Wnt/β-catenin signaling (PMID:39228688).

Mechanistic history

Synthesis pass · year-by-year structured walk · 9 steps
  1. 1999 Medium

    Established that GIRK3 is not an orphan subunit but co-assembles with GIRK1 into functional Gβγ-gated K+ channels, defining its molecular identity as a GIRK channel subunit.

    Evidence Patch-clamp electrophysiology of GIRK1/GIRK3 channels in CHO cells

    PMID:10341034

    Open questions at the time
    • Single in vitro reconstitution, no native-tissue confirmation in this study
    • Did not address other partner subunits or physiological context
  2. 2000 High

    Showed GIRK3 also partners with GIRK2 to form channels with distinct (lower) Gβγ sensitivity, revealing that subunit composition tunes channel gating properties.

    Evidence Patch-clamp, co-immunoprecipitation from transfected cells and native brain tissue

    PMID:10956667

    Open questions at the time
    • Functional consequence of reduced Gβγ sensitivity in neurons not yet tested
    • Stoichiometry of native complexes not resolved
  3. 2002 High

    Demonstrated a defined neuronal function: GIRK2/GIRK3 channels mediate acute opioid hyperpolarization of locus ceruleus neurons, linking the subunit to GPCR-driven inhibition.

    Evidence Brain slice patch-clamp in Kir3.2, Kir3.3, and double-KO mice with pharmacology

    PMID:12040038

    Open questions at the time
    • Relative contribution of GIRK3 alone (vs GIRK2) not isolated
    • Did not address GIRK3 role outside locus ceruleus
  4. 2003 Medium

    Revealed unusual axonal/presynaptic sorting of GIRK3 in hippocampal GABAergic interneurons, distinguishing its trafficking from somatodendritic Kir3 subunits.

    Evidence Immunocytochemistry and EM in primary cultures and tissue

    PMID:14664820

    Open questions at the time
    • Sorting determinants and functional role of axonal GIRK3 not established
    • Single lab, descriptive localization only
  5. 2008 Medium

    Genetic KO placed GIRK3 in a convergent multi-receptor analgesic pathway and identified cis-acting strain variation in Kcnj9 expression, connecting the gene to pharmacogenetic differences.

    Evidence Kcnj9-KO hot-plate analgesia plus QTL/haplotype mapping in F2 mice

    PMID:18300945

    Open questions at the time
    • Circuit/cell-type basis of attenuated analgesia not mapped
    • Causal cis-element not identified
  6. 2009 Medium

    Extended GIRK3's behavioral role to sedative-hypnotic and ethanol withdrawal, showing reduced expression attenuates withdrawal severity.

    Evidence Kcnj9-null mice in withdrawal behavioral assays across multiple drugs

    PMID:19759313

    Open questions at the time
    • Underlying circuit and channel-level mechanism not defined
    • Single lab behavioral readout
  7. 2010 High

    Defined the protein interactome of GIRK3: stable assembly with GABA-B receptors as GIRK1/GIRK3 tetramers, and direct C-terminal binding to NCAM and TrkB with TrkB controlling surface expression.

    Evidence BRET, reciprocal co-IP, surface biotinylation, Xenopus oocyte electrophysiology, TrkB-KO mice

    PMID:20610389 PMID:20846323

    Open questions at the time
    • Structural basis of C-terminal interactions not resolved
    • In vivo significance of NCAM/TrkB regulation in adult circuits not fully established
  8. 2016 High

    Linked GIRK3 to addiction circuitry: it gates VTA dopamine-neuron sensitivity to ethanol (with viral rescue) and is required for methamphetamine-induced plasticity of GABA-B/GIRK signaling.

    Evidence GIRK3-KO mice, VTA viral re-expression, microdialysis, slice electrophysiology, pharmacology, behavior

    PMID:25964320 PMID:26985023

    Open questions at the time
    • Molecular link between GIRK3 subunit composition and ethanol excitation not fully mechanistic
    • Signaling intermediary for methamphetamine plasticity downstream of D1/D2 not identified
  9. 2024 Medium

    Established a non-neuronal role: GIRK3 restrains endochondral bone formation and bone mass via KOR signaling in chondrocytes and Wnt/β-catenin signaling in osteoblasts.

    Evidence Germline and Col1a1-Cre conditional Girk3 KO, microCT, histomorphometry, primary chondrocyte/BMSC cultures, KOR ligand and Wnt inhibitor treatments

    PMID:35314385 PMID:39228688

    Open questions at the time
    • Whether GIRK3 acts as a K+ channel or scaffold in skeletal cells not resolved
    • Mechanism linking K+ flux to cAMP/CREB and Wnt outputs unknown

Open questions

Synthesis pass · forward-looking unresolved questions
  • How GIRK3 subunit incorporation mechanistically converts upstream GPCR signals into the diverse cell-type-specific outputs (neuronal excitability, dopamine sensitivity, bone formation) remains unresolved.
  • No structural model of GIRK3-containing channels or its interaction interfaces
  • Unclear whether skeletal phenotypes require channel conductance or scaffolding function
  • Channel-level basis of withdrawal and analgesia phenotypes undefined

Mechanism profile

Synthesis pass · controlled-vocabulary classification · explore literature graph →
Molecular activity
GO:0005215 transporter activity 3 GO:0005198 structural molecule activity 2 GO:0098772 molecular function regulator activity 2
Localization
GO:0005856 cytoskeleton 2 GO:0005886 plasma membrane 1
Pathway
R-HSA-112316 Neuronal System 3 R-HSA-162582 Signal Transduction 3 R-HSA-1266738 Developmental Biology 2
Partners
GABBR1GABBR2KCNJ3KCNJ6NCAM1NTRK2
Complex memberships
GABA-B receptor-GIRK1/GIRK3 complexGIRK1/GIRK3 channelGIRK2/GIRK3 channel

Evidence

Reading pass · 13 per-paper findings extracted from the source corpus
Year Finding Method Journal Conf PMIDs
1999 GIRK3 (Kir3.3) co-assembles with GIRK1 to form functional heteromultimeric G-protein-gated inwardly rectifying K+ channels in CHO cells; the GIRK1/GIRK3 channel has nearly identical single-channel conductance, kinetics, and Gβγ sensitivity compared to GIRK1/GIRK2 and GIRK1/GIRK4 channels. Patch-clamp electrophysiology and CHO cell expression system The Journal of membrane biology Medium 10341034
2000 GIRK2 and GIRK3 co-assemble to form functional heteromultimeric GIRK channels in CHO-K1 cells; these GIRK2/GIRK3 channels have approximately 5-fold lower sensitivity to activation by Gβγ compared to GIRK1-containing channels. GIRK2/GIRK3 complexes were immunoprecipitated from transfected cells and purified from native brain tissue. Patch-clamp electrophysiology, co-immunoprecipitation, co-transfection in CHO-K1 cells The Journal of biological chemistry High 10956667
2002 G-protein-gated K+ channels containing Kir3.2 (GIRK2) and Kir3.3 (GIRK3) subunits mediate acute opioid ([Met]5enkephalin)-induced hyperpolarization of locus ceruleus neurons; Kir3.2/3.3 double knockout abolished ~80% of the opioid-sensitive current, and residual current was blocked by Ba2+/Cs+. The cAMP-dependent cation conductance does not contribute significantly to acute opioid inhibition. Brain slice patch-clamp electrophysiology in Kir3.2 KO, Kir3.3 KO, and Kir3.2/3.3 double KO mice The Journal of neuroscience High 12040038
2003 Kir3.3 (GIRK3) protein is specifically sorted to axons in a population of large GABAergic interneurons in the CA3 region of rodent hippocampus, where it colocalizes with the vesicular GABA transporter in large synaptic terminals; this axonal sorting is distinct from the somatodendritic localization of most Kir3 subunits. Immunocytochemistry, primary hippocampal subarea cultures, light and electron microscopy Molecular and cellular neurosciences Medium 14664820
2008 Kir3.3 (GIRK3) protein is expressed in serotonergic supraependymal axons of dorsal raphe neurons at the light and electron microscopic level, with no other Kir3 subfamily members or KATP subunits detectable in these axons, suggesting a role in excitability autoregulation of these fibers. Immunocytochemistry (light and electron microscopy) Neuroscience letters Low 18755244
2008 Kcnj9 (GIRK3) knockout mice have attenuated analgesic responses to opioid (morphine), α2-adrenergic (clonidine), and cannabinoid (WIN55,212-2) drugs, placing GIRK3 in the pathway of multi-drug analgesic signaling; differential expression of Kcnj9 in the periaqueductal gray between 129P3 and C57BL/6 strains is driven by cis-acting genetic elements. QTL mapping in F2 mice, in silico haplotype analysis, Kcnj9 knockout phenotyping with hot-plate analgesia assay Pharmacogenetics and genomics Medium 18300945
2009 Kcnj9 (GIRK3) null mutant mice exhibit significantly less severe withdrawal from pentobarbital, zolpidem, and ethanol compared to wild-type littermates, demonstrating a role for GIRK3 in sedative-hypnotic withdrawal; reduced Kcnj9 expression is associated with attenuated withdrawal severity. Generation of Kcnj9-null mice, sedative-hypnotic withdrawal behavioral assays The Journal of neuroscience Medium 19759313
2010 GABA-B receptors form stable protein complexes with GIRK channels containing the GIRK1 and GIRK3 subunits (GIRK1/GIRK3 heterotetramers); BRET measurements in living cells showed direct interaction, and co-IP confirmed complexes in HEK-293 cells and in vivo in cerebellar granule cells. These receptor-channel complexes are likely assembled shortly after biosynthesis in the ER/Golgi. Bioluminescence resonance energy transfer (BRET), co-immunoprecipitation, confocal and electron microscopy in HEK-293 cells and native cerebellar tissue The European journal of neuroscience High 20846323
2010 Kir3.3 (GIRK3) directly binds to NCAM and TrkB via its C-terminal intracellular domain; TrkB co-expression increases Kir3.1/3.3-mediated K+ currents in Xenopus oocytes, while NCAM co-expression reduces this enhancement; TrkB regulates cell surface expression of Kir3.3 (but not Kir3.2), and TrkB-deficient mice have reduced Kir3.3 at the plasma membrane; premature expression of Kir3.1/3.3 in hippocampal neurons reduces NCAM-induced neurite outgrowth. Co-immunoprecipitation, surface biotinylation, Xenopus oocyte electrophysiology, immunocytochemistry, TrkB-KO mouse analysis The Journal of biological chemistry High 20610389
2015 GIRK3 expression in the ventral tegmental area (VTA) gates the mesolimbic dopaminergic pathway response to ethanol; GIRK3 KO mice show blunted ethanol-induced excitation of VTA neurons and reduced dopamine release in the nucleus accumbens; viral re-expression of GIRK3 in VTA rescued the KO phenotype and reduced ethanol binge drinking, demonstrating that VTA GIRK channel subunit composition determines DA neuron sensitivity to ethanol. GIRK3 KO mice, viral vector-mediated re-expression in VTA, in vivo microdialysis (dopamine), brain slice electrophysiology, voluntary ethanol consumption assays Proceedings of the National Academy of Sciences of the United States of America High 25964320
2016 The GIRK3 subunit is required for methamphetamine-induced attenuation of GABA-B receptor-activated GIRK currents in VTA dopamine neurons; this methamphetamine-dependent plasticity requires both D1R-like and D2R-like receptor activation and is independent of GABA-B R2 subunit dephosphorylation. Brain slice patch-clamp electrophysiology in GIRK3 KO and wild-type mice, pharmacological receptor antagonism, repeated methamphetamine treatment paradigm The Journal of neuroscience High 26985023
2022 GIRK3 controls endochondral bone formation in non-excitable chondrocytes; Girk3-/- mice have longer femurs and tibiae, and Girk3-/- chondrocytes show enhanced responsiveness to the kappa opioid receptor ligand dynorphin (greater pCREB, cAMP, and GAG production; upregulation of Col2a1 and Sox9), along with reduced VEGF receptor expression and delayed vascularization of bone. Girk3-/- mouse skeletal phenotyping, primary chondrocyte cultures, in vitro micromass assays, KOR ligand stimulation, gene expression analysis, bone imaging Bone Medium 35314385
2024 Girk3 deletion in osteoblasts/osteocytes (via 2.3 kb-Col1a1-Cre) is sufficient to increase bone mass and bone strength in male mice; Girk3-/- bone marrow stromal cells are more proliferative and osteogenic, with altered Wnt pathway gene expression; Wnt/β-catenin inhibition prevents enhanced mineralization in Girk3-/- cells. Conditional KO (Col1a1-Cre), germline Girk3-/- mice, microCT, histomorphometry, in vitro BMSC and calvarial osteoblast cultures, Wnt inhibitor treatments JBMR plus Medium 39228688

Source papers

Stage 0 corpus · 20 papers · ranked by NIH iCite citations
Year Title Journal Citations PMID
2002 G-protein-gated potassium channels containing Kir3.2 and Kir3.3 subunits mediate the acute inhibitory effects of opioids on locus ceruleus neurons. The Journal of neuroscience : the official journal of the Society for Neuroscience 163 12040038
2000 Functional and biochemical evidence for G-protein-gated inwardly rectifying K+ (GIRK) channels composed of GIRK2 and GIRK3. The Journal of biological chemistry 88 10956667
1999 Functional expression and characterization of G-protein-gated inwardly rectifying K+ channels containing GIRK3. The Journal of membrane biology 50 10341034
2015 GIRK3 gates activation of the mesolimbic dopaminergic pathway by ethanol. Proceedings of the National Academy of Sciences of the United States of America 49 25964320
2009 Mapping a barbiturate withdrawal locus to a 0.44 Mb interval and analysis of a novel null mutant identify a role for Kcnj9 (GIRK3) in withdrawal from pentobarbital, zolpidem, and ethanol. The Journal of neuroscience : the official journal of the Society for Neuroscience 49 19759313
2010 Evidence for oligomerization between GABAB receptors and GIRK channels containing the GIRK1 and GIRK3 subunits. The European journal of neuroscience 48 20846323
2008 Quantitative trait locus and computational mapping identifies Kcnj9 (GIRK3) as a candidate gene affecting analgesia from multiple drug classes. Pharmacogenetics and genomics 46 18300945
2016 A Role for the GIRK3 Subunit in Methamphetamine-Induced Attenuation of GABAB Receptor-Activated GIRK Currents in VTA Dopamine Neurons. The Journal of neuroscience : the official journal of the Society for Neuroscience 32 26985023
2003 Axonal sorting of Kir3.3 defines a GABA-containing neuron in the CA3 region of rodent hippocampus. Molecular and cellular neurosciences 24 14664820
2010 Functional consequences of the interactions among the neural cell adhesion molecule NCAM, the receptor tyrosine kinase TrkB, and the inwardly rectifying K+ channel KIR3.3. The Journal of biological chemistry 20 20610389
2001 Analysis of linkage disequilibrium between polymorphisms in the KCNJ9 gene with type 2 diabetes mellitus in Pima Indians. Molecular genetics and metabolism 20 11350189
2000 Genomic structure and expression of human KCNJ9 (Kir3.3/GIRK3). Biochemical and biophysical research communications 18 10913335
2022 GIRK3 deletion facilitates kappa opioid signaling in chondrocytes, delays vascularization and promotes bone lengthening in mice. Bone 8 35314385
2024 Girk3 deletion increases osteoblast maturation and bone mass accrual in adult male mice. JBMR plus 2 39228688
2008 Expression of Kir3.3 potassium channel subunits in supraependymal axons. Neuroscience letters 2 18755244
2025 Atp1a2 and Kcnj9 Are Candidate Genes Underlying Sensitivity to Oxycodone-Induced Locomotor Activation and Withdrawal-Induced Anxiety-Like Behaviors in C57BL/6 Substrains. Genes, brain, and behavior 1 39801366
2026 The circ-GLG1/miR-346/KCNJ9 axis drives malignant progression of bladder cancer by modulating KCNJ9 expression. Experimental cell research 0 41490595
2025 Global but not myeloid lineage-directed Girk3 deletion increases bone mass in female mice. JBMR plus 0 41084512
2024 Atp1a2 and Kcnj9 are candidate genes underlying sensitivity to oxycodone-induced locomotor activation and withdrawal-induced anxiety-like behaviors in C57BL/6 substrains. bioRxiv : the preprint server for biology 0 38798314
2023 De Novo Variant in the KCNJ9 Gene as a Possible Cause of Neonatal Seizures. Genes 0 36833293

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