Potassium inward rectifying (Kir) channels are a class of transmembrane proteins which play important roles in various physiological processes, controlling the resting membrane potential, regulating excitability of cardiac cells and neurons, coupling insulin secretion and maintaining electrolyte balance.Kir channels prefer to conduct inward currents at membrane voltages negative to the K+ equilibrium potential other than outward currents at voltages positive to it, even with equal K+ concentrations on both sides of the membrane.This conduction property, named as inward rectification,is not an inherent property of the channel protein itself, but reflects strong voltage dependence of channel block by intracellular cations such as Mg2+ and polyamines.