Synergistic actions of Ca²⁺ and the phorbol ester TPA on K⁺-induced catecholamine release from bovine adrenal chromaffin cells

Enhancement of Ca²⁺-dependent high K⁺-evoked catecholamine secretion was observed after pretreatment of cultured bovine adrenal chromaffin cells with the phorbol ester 4B-phorbol 12-myristate 13-acetate (TPA) in the absence of added extracellular Ca²⁺. This effect of TPA was not reproduced when the secretagogues acetylcholine, nicotine, or veratrine were substituted for high K⁺. The implications of these results are discussed in relation to the role of protein kinase C in stimulus-secretion coupling in the chromaffin cell.