INVOLVEMENT OF PROTEIN KINASE C IN THE REGULATION OF Na+/Ca2+ EXCHANGER IN BOVINE ADRENAL CHROMAFFIN CELLS

P>The Na+/Ca2+ exchanger (NCX) exchanges Na+ and Ca2+ bidirectionally through the forward mode (Ca2+ extrusion) or the reverse mode (Ca2+ influx). The present study was undertaken to clarify the role of protein kinase C (PKC) in the regulation of NCX in bovine adrenal chromaffin cells. The Na+-loaded cells were prepared by treatment with 100 mu mol/L ouabain and 50 mu mol/L veratridine. Incubation of Na+-loaded cells with Na+-free solution in the presence of the Ca2+ channel blockers nicardipine (3 mu mol/L) and omega-conotoxin MVIIC (0.3 mu mol/L) caused Ca2+ uptake and catecholamine release. The Na+-dependent Ca2+ uptake and catecholamine release were inhibited by 2-[4-[(2,5-difluorophenyl)methoxy]phenoxy]-5-ethoxyaniline (SEA0400; 1 mu mol/L) and 2-[2-[4-(4-nitrobenzyloxy)phenyl]isothiourea (KB-R7943; 10 mu mol/L), both NCX inhibitors. These results indicate that the Na+-dependent responses are mostly due to activation of the NCX working in the reverse mode. In addition, we examined the effects of PKC inhibitors and an activator on the NCX-mediated Ca2+ uptake and catecholamine release. Bisindolylmaleimide I (0.3-10 mu mol/L) and chelerythrine (3-100 mu mol/L), both PKC inhibitors, inhibited NCX-mediated responses. In contrast, phorbol 12,13-dibutyrate (0.1-10 mu mol/L), a PKC activator, enhanced the responses. Bisindolylmaleimide I and chelerythrine, at effective concentrations for inhibition of Na+-dependent catecholamine release, had a little or no effect on high K+-induced catecholamine release in intact cells or on Ca2+-induced catecholamine release in beta-escin-permeabilized cells. These results suggest that PKC is involved in the activation of NCX in bovine adrenal chromaffin cells.