Superoxide anion release by human endothelial cells: Synergism between a phorbol ester and a calcium ionophore

Abstract

Abstract In order to study the signal transduction mechanism of human endothelial cells (EC), the regulation of superoxide anion (O 2 − ) release in EC has been investigated using the calcium ionophore A23187 and phorbol myristate acetate (PMA), a potential activator of the Ca 2+ activated, phospholipid‐dependent protein kinase, designated “protein kinase C.” PMA enhanced O 2 − release from EC, and this enhancement occurred regardless of the presence or absence of extracellular Ca 2+ . A similar increase was produced by A23187; omission of extracellular Ca 2+ prevented this increase. Simultaneous stimulation with PMA and A23187 produced a large increase in O 2 − release at submaximal concentrations of these agents, which, when added separately, caused minimal effects. These findings indicate that the activation of protein kinase C and mobilization of Ca 2+ evoked by PMA and A23187 respectively are synergistically effective for eliciting a full physiological response of EC in the generation and release of O 2 − .