Protein kinase c-independent inhibition of the Ca 2+-activated K + channel by angiotensin II and endothelin-1

Abstract

We previously reported that the Ca 2+-activated K + channel (K ca-channel) in cultured smooth muscle cells from porcine coronary artery was inhibited by protein kinase C (C-kinase). In this study, inhibition of the K ca-channel by receptor-mediated vascular contractile agonists, such as angiotensin II (ANG II) and endothelin-1 (ET-1), was investigated by the patch-clamp technique. In cell-attached patches, addition of ANG II (500 nM) or ET-1 (50 nM) to the bath inhibited the K ca-channel activated by the calcium ionophore A23187 (10–20 μM). Phorbol 12-myristate 13-acetate (PMA, 1 μM), a C-kinase activator, also decreased the open probability of the K ca-channel. The PMA-induced decrease in the open probability was reversed by subsequent application of staurosporine (1 nM), a C-kinase inhibitor, but the ANG II- and ET-1-induced decreases were not reversed by subsequent application of staurosporine (> 30 nM). Pretreatment of smooth muscle cells with 30 nM staurosporine, a protein kinase inhibitor, or 1 mM neomycin, an inhibitor of phospholipase C, also did not abolish the inhibition of the K ca-channel by ANG II. Furthermore, ANG II inhibited the K ca-channel in cells in which C-kinase was down-regulated. These results indicate that, in porcine coronary artery smooth muscle cells, ANG II and ET-1 inhibit the K ca-channel by a C-kinase-independent mechanism.