Protein kinase C activation stimulates calcium transport in adrenal zona glomerulosa cells

Adrenal zona glomerulosa (ZG) cells produce aldosterone in response to angiotensin II and extracellular potassium through different mechanisms which involve changes in cytosolic free calcium (Cai). Protein kinase C (PKC) activation is part of the angiotensin II signalling cascade but its effects on Cai are unknown. PKC activation with 1 microM phorbol 12-myristate 13-acetate (PMA) and 8 mM Ko significantly increased the rate of calcium influx (P < 0.001). Both the PKC- and the Ko-induced calcium influx occurred via a nifedipine-sensitive pathway. When both were combined, PKC activation and 8 mM Ko were not additive over either agent alone. PKC activation and 8 mM Ko also stimulated calcium efflux (P < 0.01). When combined together PKC activation and 8 mM Ko had additive effects on calcium efflux (P < 0.05). PKC activation did not increase Cai nor the exchangeable calcium pool in contrast to 8 mM Ko which significantly increased both (P < 0.001). Thus, PKC activation in ZG cells induces a pattern of calcium transport characterized by accelerated calcium recycling across the cell membrane without increasing cell calcium content.