Activation of ATP-sensitive K+ channels by cyclic AMP-dependent protein kinase in cultured smooth muscle cells of porcine coronary artery.

The effects of cyclic AMP-dependent protein kinase on ATP-sensitive K+ channels in cultured smooth muscle cells of the porcine coronary artery were investigated using the patch-clamp technique. Extracellular application of isoproterenol (1mM), a beta agonist, or forskolin (2 x 10(-5)M), an activator of adenylate cyclase, activated these channels in cell-attached patch configurations, which were not blocked by phorbol 12-myristate 13-acetate (10(-6)M), an activator of protein kinase C. Cyclic AMP-dependent protein kinase activated these channels in inside-out patch configurations. These results suggest that cyclic AMP-dependent phosphorylation modulates ATP-sensitive K+ channels, in addition to its well known effects on Ca(2+)-activated K+ channels. The activation of ATP-sensitive K+ channels by cyclic AMP-dependent phosphorylation contributes to hyperpolarization of the membrane and to the relaxation of vascular smooth muscle cells.