The beta gamma subunits of GTP-binding proteins activate the muscarinic K+ channel in heart.

Subunits of guanine nucleotide regulatory proteins purified from bovine cerebral cortex were used to perfuse the intracellular surface of excised patches of chick embryonic atrial cells. Single-channel current measurements unexpectedly indicate that the beta gamma, and not the alpha subunits, are responsible for activating the muscarinic-gated potassium channel.