Phosphatidic Acid-Induced Superoxide Generation in Electropermeabilized Human Neutrophils

The ability of phosphatidic acid to induce O−2 generation was examined in intact and electropermeabilized neutrophils. In intact cells, after a long lag (∼11 min), 1,2-didecanoylphosphatidic acid (PA10, 10 μM) elicited O−2 generation (30-40 nmol/min/107 cells at maximum) which lasted for 8-9 min. Electropermeabilization facilitated the response by shortening the lag (within 30s) and enhancing the maximal rate (120-130 O−2 nmol/min/ 107 cells). The induction by PA10 was concentration-dependent and the half-maximal concentrations for intact and permeabilized cells were 11 and 3 μM, respectively. In permeabilized cells, the rate of O−2 release by PA10, which was similar to that by fMet-Leu-Phe or phorbol myristate acetate, was not enhanced by addition of dioctanoylglycerol. Also, the response was unaffected by propranolol, an inhibitor of phosphatidate-phosphohydrolase that converts phosphatidic acid to diacylglycerol. Phosphatidic acids with longer acyl chains (C12-C14) also activated the permeabilized cells, although the degree of activation decreased as the chain length was increased. These results indicate the ability of phosphatidic acid to induce respiratory burst independently of diacylglycerol and support the idea that phosphatidic acid can be an activator of NADPH oxidase in human neutrophils.