FUNCTIONAL EXPRESSION FROM COMPLEMENTARY-DNA OF A RAT ATRIAL INWARDLYRECTIFYING POTASSIUM CHANNEL

Complementary DNAs encoding two types of inwardly rectifying K+ channe ls, GIRK1 and IRK1, have been cloned from rat atrium and mouse macroph age, respectively. GIRK1 expressed in Xenopus oocytes was activated by acetylcholine (ACh) when m2 muscarinic ACh receptor was co-expressed. The ACh-induced activation of GIRK1 was not enhanced by co-expression with the GTP-binding protein (G-protein) alpha-subunits. On the other hand, the ACh-induced GIRK1 was increased by co-expression with the G -protein beta gamma-subunits. However, the IRK1 channel was not activa ted by the G-protein alpha-subunits and beta gamma-subunits. These fin dings clarified that the GIRK1 channel was not regulated by the G-prot ein alpha-subunits, but by the beta gamma-subunits alone.