Requirement of calcium influx for hydrolytic action of membrane phospholipids by cytosolic phospholipase A2 rather than mitogen-activated protein kinase activation in Fc epsilon RI-stimulated rat peritoneal mast cells.

The mechanism by which cytosolic phospholipase A2 (cPLA2) is not responsible for eicosanoid production in rat peritoneal mast cells upon antigen stimulation [Ishimoto et al. (1996) J. Biochem. 120, 616-623] was investigated in the mast cells stimulated by cross-linking of the IgE receptor or with thapsigargin. Stimulation with thapsigargin, but not with antigen, resulted in apparent lysophosphatidylcholine (lysoPC) formation. Antigen stimulation significantly increased the activities of mitogen-activated protein (MAP) kinase and cPLA2. These activities were further potentiated by phorbol ester. The antigen elicited a rapid and transient increase in intracellular Ca2+ concentration, while thapsigargin produced a slow and sustained increase. Furthermore, a combination of antigen and thapsigargin rapidly increased and prolonged the intracellular Ca2+ concentration. Under these conditions, lysoPC was apparently generated, whereas it was not in response to antigen alone. These results suggest that a prolonged increase in the intracellular Ca2+ concentration is required for cPLA2 to associate with membranes, thus leading to hydrolysis of membrane phospholipids by the enzyme.