G protein-gated inwardly rectifying potassium channel (GIRK (also known as Kir3))

G protein-gated inwardly rectifying potassium channels (GIRKs, also called Kir3 channels) are a family within the larger group of inwardly rectifying potassium ion channels. They are directly activated by βγ-subunits released from heterotrimeric G proteins following stimulation of various G protein-coupled receptors (GPCRs) such as muscarinic acetylcholine receptors, adenosine A₁ receptors, dopamine D₂ receptors, opioid receptors among others. Upon activation—requiring both PIP₂ lipid cofactor and direct interaction with Gβγ—the channels allow K⁺ ions into cells more easily than outwards flow (“inward rectification”), resulting in hyperpolarization that reduces cell excitability. In the central nervous system (CNS), they play critical roles regulating synaptic transmission and neuronal firing rates; dysfunction is implicated in epilepsy, mood disorders including depression/schizophrenia/bipolar disorder/anxiety disorders as well as substance abuse/addiction. In the heart—especially atrial myocytes—they mediate parasympathetic slowing via muscarinic signaling pathways. Therapeutically relevant modulation can be achieved either indirectly through targeting upstream GPCRs or directly using small-molecule modulators developed for research purposes. However safety concerns exist due to their widespread physiological roles across tissues.[1][2][3][4][5]

Other names

G protein-coupled inwardly rectifying potassium channelGIRK channelKir3 channelInwardly rectifying potassium channel, subfamily J, member 3/6/9/5 (for specific subunits)Muscarinic potassium channel (I_KACh) [when referring to cardiac heterotetramers]

– Direct activation by binding small molecules to allosteric sites on the channels themselves (e.g., ML297 activates certain GIRKs independently of G-proteins). – Indirect activation via release of Gβγ subunits from activated GPCRs leading to opening/hyperpolarization effect on target cells. – Modulation by endogenous lipids such as PIP₂ is required for gating; some drugs alter this interaction or mimic it.