A group of potassium channels with a predicted membrane topology of two TMDs (M1–M2) and a pore (P) domain comprises inward rectifier channels (K_ir) and ATP-sensitive (K_ATP) channels. Currently, seven subfamilies (Kir1–7) have been identified, the majority of which form K⁺ channels with varying degrees of inward rectification when expressed in heterologous expression systems. They can be classified into four functional groups: classical Kir channels (Kir2.x) are constitutively active, G protein-gated Kir channels (K_G or Kir3.x) are regulated by G protein-coupled receptors, ATP-sensitive K⁺ channels (Kir6.x) are tightly linked to cellular metabolism, and K⁺ transport channels (Kir1.x, Kir4.x, Kir5.x, and Kir7.x) [1].