Regulations by cyclic nucleotides and phorbol ester of calcium efflux from cultured bovine adrenal chromaffin cells

Abstract

The effects of cyclic nucleotides and phorbol ester on Ca 2+ efflux from cultured bovine adrenal chromaffin cells were examined. Dibutyryl cyclic AMP (DB-cAMP), forskolin (an activator of adenylate cyclase ), dibutyryl cyclic GMP (DB-cGMP) and nitroprusside (an activator of guanylate cyclase) all stimulated 45Ca 2+ efflux from the cells preloaded with 45Ca 2+. These agents did not increase the intracellular free Ca 2+ ([Ca 2+]i) level. On the contrary, phorbol 12-myristate 13-acetate (PMA; an activator of protein kinase C) did not affect the efflux of 45Ca 2+, but inhibited the increase in 45Ca 2+ efflux caused by DB-cAMP, forskolin, DB-cGMP or nitroprusside. The 45Ca 2+ effluxes stimulated by cyclic nucleotides, forskolin and nitroprusside were inhibited by deprivation of extracellular Na + ([Na +]o). These results suggest that both cAMP- and cGMP-dependent protein kinases are involved in the stimulatory mechanism of [Na +]o dependent Ca 2+ efflux, probably through acceleration of [Na +]o [Ca 2+]i exchange and that protein kinase C plays an inhibitory role in this mechanism.