Inward-rectifier potassium channels (Kir, IRK) are a specific lipid-gated subset of potassium channel ^[1]. There are seven subfamilies of Kir channels, denoted as Kir1 – Kir7, Each subfamily has multiple members (Kir1.1, Kir2.1-Kir2.4, Kir3.1-Kir3.4, Kir4.1-Kir4.2, Kir5.1, Kir6.1-Kir6.2, Kir7.1) that have nearly identical amino acid sequences across known mammalian species ^[2].

Kir channels are formed from as homotetrameric membrane proteins. Each of the four identical protein subunits is composed of two membrane-spanning alpha helices (M1 and M2). Heterotetramers can form between members of the same subfamily (i.e. Kir2.1 and Kir2.3) when the channels are overexpressed ^[1].

Cholesterol-binding sites in GIRK channels were located in the same regions as in Kir2.1, the principal cholesterol-binding pocket in these 2 GIRK channels was located at the center of the transmembrane domain ^[3]. A second putative cholesterol-binding site was also identified in GIRK2 in the transmembrane domain close to its interface with the cytosolic domain at a similar location to the transient binding site in Kir2.1 ^[4]. Site-directed mutagenesis and patch-clamp electrophysiology were used to identify Val168 or Asn171 in the upper site, which are unique to ROMK within the Kir channel family, led to a dramatic reduction in VU591 sensitivity ^[5].

Yellow: Site-directed mutagenesis of Kir7.1 channel pore-lining amino acid residues identified Glutamate 149 and Alanine 150 as essential determinants of VU714 activity ^[6].

VU6036720 inhibits Kir4.1/5.1 activity through a reduction of channel open-state probability and single-channel current amplitude. Elevating extracellular potassium ion by 20 mM shifted the IC₅₀ 6.8-fold, suggesting that VU6036720 is a pore blocker that binds in the ion-conduction pathway ^[11]. Green: Mutation of the "rectification controller" asparagine 161 (N161) to glutamate (Kir4.1/Kir5.1), which is equivalent to small-molecule binding sites in other Kir channels, led to a strong reduction of inhibition ^[11]. ML418 is sub-micromolar pore blocker of Kir7.1 potassium channel ^[12].

CL-705G is a novel chemical Kir6.2-specific KATP channel opener, it activated Kir6.2Δ36 in the presence of SUR2A, but not when expressed by itself. Further, three amino acids, I296, T294, and v291 in the C-linker domain of Kir6.2 were found critical for forming the binding pocket ^[7]. Mutation of the "rectification controller" asparagine 161 (N161) to glutamate (Kir4.1/Kir5.1), which is equivalent to small-molecule binding sites in other Kir channels, led to a strong reduction of inhibition ^[8]. Terfenadine: It acts as a slow channel blocker on Kir6.2Δ26 channels. Terfenadine-induced block of Kir6.2Δ26 channels demonstrated no marked voltage dependence, but lowering the intracellular pH to 6.5 potentiated the inhibition of Kir6.2Δ26 channels by terfenadine ^[9]. Diverse compounds exist that can either inhibit (block) or activate (open) KATP channel activity. The vast majority of KATP channel activators and blockers act by binding to the SURx subunit ^[10].

The structure of hKir6.2 (C166S, G334D) has an open pore. The radius of the ion pathway at the inner helix gate is ~3.3 Å compared to ~1.0 Å in hKir6.2 (WT). Expansion of the ion pathway is associated with rotation of the L164 and F168 side chains and modest conformational changes within the intracellular half of the inner and outer helices ^[13].