Protein Kinase C Modulates Ca²⁺ -Activated K⁺ Channels in Cultured Rat Mesenteric Artery Smooth Muscle Cells

Abstract

The electrical and pharmacological properties of protein kinase C (PKC) and its effect its effect on the single Ca²⁺ -activated K⁺ channel (Kca-channel) in the cultured smooth muscle cells of rat mesenteric artery were studied using a patch-clamp technique. The Kca-channel had a slope conductance of 151±7 pS (mean±S.E.) in symmetrical 142 mM K solutions. The high conductance K⁺ channel, applied to the outer side of membrane patches, was potently inhibited by charybdotoxin (0.1 μM) and tetraethylammonium (0.5 μM), but not by apamin (0.4 μM.). In cell-attached patches, bath application of phorbol 12-myristate 13-acetate (PMA, 2 μM), a PKC activator, inhibited the activity of the Kca-channel in the presence of the Ca²⁺ ionophore, A 23187 (10 μM). This inhibition was reversed by subsequent application of staurosporine (1 nM), a PKC inhibitor. Application of 1-oleoyl-2-acetylglycerol (OAG, 30 μM), another PKC activator, also inhibited the A 23187-induced activation of the K⁺ channel, and this inhibition was reversed by staurosporine. In inside-out patches, bath application of PKC (0.2 munits), in the presence of ATP (1 mM) and PMS (1 μM), inhibited the K⁺ channel. These results indicate that protein kinase C inhibits the Ca²⁺ -activsted K⁺ channel of mesenteric artery smooth muscle cells in the rat.