Phorbol esters induce a slow, non-cytotoxic release of histamine from rat peritoneal mast cells

The phorbol ester 12-O-tetradecanoylphorbol-13-acetate (TPA) and the synthetic diacylglycerol, 1-oleoyl-2-acetylglycerol (OAG) were employed to investigate the consequences of protein kinase C activation in rat peritoneal mast cells. TPA (10 ng/ml) induced a biphasic release of histamine from mast cells. At short periods of incubation histamine release was low; about 10% at 10 min. At 15 min a second phase of release commenced, achieving a maximum at 90 min incubation by which time about 70% of cell histamine was released. Histamine release by TPA was dependent on glycolytic and oxidative metabolism, temperature-dependent and occurred in purified mast cells. In contrast, histamine release induced by OAG 50 micrograms/ml was maximal after 20 min. Studies using RHC 80267, a diacylglycerol (DAG) lipase inhibitor, indicated that metabolism of OAG by DAG lipase as well as spontaneous degradation accounts for the comparatively short-lived response to OAG.