K_ir3.1 (or G-protein regulated Inward-Rectifier K⁺ channel, GIRK1) is a member of the family of inward rectifying K⁺ channels. The family includes 15 members that are structurally and functionally different from the voltage-dependent K⁺ channels.

The family’s topology consists of two transmembrane domains that flank a single and highly conserved pore region with intracellular N- and C-termini. As is the case for the voltage-dependent K+ channels the functional unit for the K_ir channels is composed of four subunit that can assembly as either homo or heterotetramers.

K_ir channels are characterized by a K⁺ efflux that is limited by depolarizing membrane potentials thus making them essential for controlling resting membrane potential and K⁺ homeostasis.

K_ir3.1 is a member of the K_ir3.x subfamily that includes four members (K_ir3.1- K_ir3.4). The K_ir3 family is characterized by the fact that the channels can be activated by neurotransmitters and other factors acting via the activation of G-protein coupled receptors. Binding of the corresponding ligand to the G-protein receptor induces the dissociation of Ga-GTP from the Gbg dimer. The latter directly binds to K_ir3 and activates the channel.^1,3

In the heart, K_ir3.1 co-assembles with K_ir3.4 to form the prototypical muscarinic-gated K⁺ channel K_Ach current, responsible for slowing the heart rate in response of parasympathetic stimulation.²

In the brain, K_ir3.1 co-assembles with K_ir3.2 and mediates the inhibitory effects of many neurotransmitters including opioid, adrenergic, muscarinic, dopaminergic and -aminobutyric acid (GABA).^1,3

A peptide toxin originating from the Apis mellifera bee venom, Tertiapin (#RTT-250) was shown to be a potent blocker of K_ir3.1 containing channels (8.6nM for the K_ir3.1/3.4 combination and 5.4nM for the K_ir3.1/3.2).^4,5