Importance of basal and agonist-stimulated intracellular calcium for superoxide anion generation in peritoneal macrophages

The cellular signalling mechanisms initiated by platelet-activating factor (PAF) for stimulation of superoxide anion (O2-) generation in peritoneal macrophages were investigated by monitoring intracellular calcium ([Ca2+](i)) levels. In rat peritoneal macrophages, exogenous PAF elicited an increase in [Ca2+](i), but there was no O2- generation. PAF elicited similar increases in [Ca2+](i) in guinea pig macrophages, which were accompanied by O2- generation. Removal of external calcium revealed that the major component of the PAF-induced increase in [Ca2+](i), in both rat and guina pig peritoneal macrophages, was dependent on transmembrane Ca2+ flux. Pertussis toxin pretreatment had no effect on basal or PAF-induced increases in [Ca2+](i). In guinea pig macrophages, removal of external calcium or pertussis toxin pretreatment reduced O2- generation by approximately 50 and the combination of these pretreatments caused almost complete suppression of the response. Thus, additional second mesenger systems are activated in guinea pig macrophages following PAF receptor activation which appear to be essential for O2- generation.