[IgE-receptor stimulation induces biphasic 1,2-diacylglycerol production in RBL-2H3 cells. Phosphatidylcholine hydrolysis by phospholipase D plays a major role in the second sustained 1,2-diacylglycerol accumulation].

: Activation of RBL-2H3 cells by cross-linking their IgE receptors resulted in a biphasic increase in cellular 1,2-diacylglycerol (DG) content. The first-phase DG production was coincident with a transient breakdown of phosphatidylinositol 4,5-bisphosphate (PIP2). The second large sustained phase of DG accumulation appeared to be derived mainly from phosphatidylcholine (PC) and partly from phosphatidylinositol (PI). The accumulation of phosphatidylethanol (PEt) and the reduction of DG formation in the presence of ethanol suggested that more than 50% of the DG due to PC hydrolysis was formed through the action of phospholipase D. The addition of phorbol myristate acetate or Ca2+ ionophore A23187 stimulated the hydrolysis of PC. In protein kinase C (PKC) down-regulated cells, PC hydrolysis induced by A23187 was markedly suppressed. Taken together, these results lead as to speculate that hydrolysis of PC is regulated by the increase in cellular Ca2+ and PKC activation through the hydrolysis of PIP2. The exocytotic response became evident with a 1 min time lag after antigen (Ag) stimulation, followed by the transient breakdown of PIP2. Ethanol inhibited Ag-stimulated serotonin secretion. The concentration-dependent inhibitory profile of secretion by ethanol correlated well with that of the sustained phase of DG accumulation. These results suggest that sustained DG production, mainly derived from PC through phospholipase D action, plays an important role in maintaining secretory response.