Phosphatidic acid (PA) dose-dependently induced Superoxide (O2 −) production of electropermeabilized human neutrophils but not of intact neutrophils, indicating that PA induces the activation of NADPH oxidase by acting on an intracellular target. The O2 − production by PA was not inhibited by protein kinase C (PKC) inhibitors, such as staurosporine and calphostin C, and an inhibitor of PA phosphohydrolase, propranolol. These observations suggest that the activation of the oxidase by PA is independent of the activity of PKC and may dominate the activation by diacylglycerol which is formed from PA via the action of PA phosphohydrolase. Furthermore, the production by PA, as well as that by phorbol myristate acetate, was inhibited by cyclic AMP and GDPßS. Therefore, PA seems to act at a site downstream of PKC.
