Primary structure and functional expression of a mouse inward rectifier K⁺ channel and a rat Gprotein-coupled muscarinic K⁺ channel

Abstract

A cDNA encoding an inward rectifier K⁺ channel (IRK1) was isolated by expression cloning. This channel conducts inward K⁺ current below the K⁺ equilibrium potential but passes little outward K⁺ current. By sequence homology with IRK1, a cDNA for a muscarinic K⁺ channel, another inward rectifying K⁺ channel which is activated by direct interaction with G-protein was isolated. In contrast with the voltage-gated K⁺ channels which have six transmembrane segments, the IRK1 channel and the GIRK1 channel contains only two putative transmembrane segments per subunit and corresponds to the inner core structure of voltagegated K⁺ channels. The IRK1 channel and the GIRK1 channel show extensive sequence similarity and constitute a new superfamily.