Protein Kinase C Inhibits the Ca2+-Activated K+ Channel of Cultured Porcine Coronary Artery Smooth Muscle Cells

Abstract

The effect of protein kinase C (C-kinase) on the Ca2+-activated K+ channel (KCa-channel) was studied in cultured smooth muscle cells from porcine coronary artery by the patch-clamp technique. In cell-attached patches, bath application of phorbol 12-myristate 13-acetate (PMA, 1 μM), a C-kinase activator, significantly decreased the open probability of the activated KCa-channel in the presence of the calcium ionophore A23187 (20 μM), which increases intracellular Ca2+. This decrease in the open probability was reversed by subsequent application of staurosporine (1 nM), a C-kinase inhibitor. Application of 1-oleoyl-2-acetylglycerol (OAG, 30 μM) or 1,2-dioctanoylglycerol (DG8; 30 μM), activators of C-kinase, also inhibited KCa-channel activation by A23187, and these inhibitions were also reversed by staurosporine. PMA (1 μM) also inhibited KCa-channel activation by dibutylyl cyclic AMP (db-cAMP, 2 mM) or caffeine (30 mM). In inside-out patches, bath application of the C-kinase fraction from rat brain in the presence of ATP (1 mM) and PMA (1 μM ) markedly inhibited the KCa-channel. These results indicate that activation of C-kinase inhibits the KCa-channel and may cause membrane depolarization and vascular contraction.