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J. Biol. Chem., Vol. 275, Issue 38, 29709-29716, September 22, 2000

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A Switch Mechanism for G Activation of I_KACh^*

Igor Medina, Grigory Krapivinsky, Susanne Arnold, Pramesh Kovoor, Luba Krapivinsky, and David E. Clapham

From the Howard Hughes Medical Institute, Children's Hospital and Harvard Medical School, Boston, Massachusetts 02115

G protein-gated inwardly rectifying potassium (GIRK) channels are a family of K⁺-selective ion channels that slow the firing rate of neurons and cardiac myocytes. GIRK channels are directly bound and activated by the G protein G subunit. As heterotetramers, they comprise the GIRK1 and the GIRK2, -3, or -4 subunits. Here we show that GIRK1 but not the GIRK4 subunit is phosphorylated when heterologously expressed. We found also that phosphatase PP2A dephosphorylation of a protein in the excised patch abrogates channel activation by G. Experiments with the truncated molecule demonstrated that the GIRK1 C-terminal is critical for both channel phosphorylation and channel regulation by protein phosphorylation, but the critical phosphorylation sites were not located on the C terminus. These data provide evidence for a novel switch mechanism in which protein phosphorylation enables G gating of the channel complex.

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