Requirement of Calcium Influx for Hydrolytic Action of Membrane Phospholipids by Cytosolic Phospholipase A2 Rather than Mitogen-Activated Protein Kinase Activation in FcεRI-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 crosslinking of the IgE receptor or with thapsigargin. Stimulation with thapsigargin, but not with antigen, resulted in apparent lysophosphatidyicholine (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.