Cloning and functional expression of a cardiac inward rectifier K+ channel.

We have isolated a cDNA coding for an inward rectifier K+ channel (RBHIK1) from rabbit heart. The cloned cDNA encodes a protein of 427 amino acids with two putative transmembrane segments. The primary structure of RBHIK1 is highly homologous to that of IRK1 which is an inward rectifier K+ channel recently cloned from mouse macrophage by expression cloning. When expressed in Xenopus oocytes, RBHIK1 current showed strong inward rectification and was inhibited by extracellular Ba2+ and Cs+. RNA blot analysis revealed the expression of RBHIK1 mRNA in various rabbit tissues, especially high level in the ventricular muscle.