Study on the diversity of the cardiac inward rectifier potassium channels

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The inward rectifier potassium (Kir) channels play an important role in maintaining the resting potential, promoting the repolarization of action potentials and controlling the cell excitability in cardiac myocytes. Kir genes in the subgroup Kir2 encode the a subunits of Kir channels that display the properties of the strong inward rectifier I_<K1> in cardiac myocytes. To explore the significance of different Kir channels in the cardiac function, we studied the electrophysiological properties of the Kir2.1 and Kir2.2 channels of the mouse and human by heterologously expressing them in mammalian cells. We found that Kir2.1 and Kir2.2 channels showed different sensitivities to the blockage by intracellular polyamines and Mg^<2+>, which function as the intrinsic Kir channel blockers. The results suggested that Kir2.1 channel underlies I_<K1> in cardiac myocytes at physiological cytoplasmic conditions. We also studied the function of the human Kir2.1 and Kir2.2 genes cloned from healthy individuals, and found a variance in the Kir2.2 gene, which caused a functional loss of the channel.