[3H]phosphatidic acid formed in response to FMLP is not inhibited by R59 022, a diacylglycerol kinase inhibitor.

R59 022 has been suggested to function as a selective inhibitor of diacylglycerol kinase in platelets and erythrocyte membranes. In the present study we have studied the effect of this drug on [3H]diacylglycerol and [3H]phosphatidic acid formed in response to FMLP in human neutrophils. Our results indicate that R59 022 (50 microM) itself (without any stimulus) caused a significant hydrolysis of [3H]phosphatidylinositol (6-7%), which resulted in an accumulation of [3H]diacylglycerol and [3H]phosphatidic acid. On the other hand, R59 022 at lower concentrations (10 microM) exhibited a biphasic response on the time-dependent formation of [3H]phosphatidic acid in response to FMLP. [3H]phosphatidic acid formed at 30 sec and 60 sec after stimulation with FMLP was neither inhibited nor stimulated whereas the amount of [3H]phosphatidic acid formed at 2 min and 3 min was significantly higher than that obtained with FMLP alone. Our results demonstrate that the increased formation of diacylglycerol and phosphatidic acid in response to FMLP in the presence of R59 022 is likely due to the activation of phospholipase C and/or D rather than the inhibition of DG kinase. We therefore conclude that R59 022 is relatively nonspecific and can affect several other enzymes involved in the agonist-stimulated turnover of phospholipids.