Aggregation of human polymorphonuclear leukocytes by endothelin: role of platelet-activating factor

Abstract The mechanisms by which endothelin-1 (ET-1) acts on polymorphonuclear leukocytes (PMN) are insufficiently known. In this study, we assessed the hypotheses that ET-1 is a PMN-aggregating agent, and that platelet-activating factor (PAF) is the principal mediator of ET-1-induced PMN aggregation. ET-1 induced dose-related PMN aggregation, which started 1 min after ET-1 exposure. Two different specific PAF receptor antagonists blocked the effect of ET-1 on PMN aggregation. In addition, FT-1 induced a significant increase in the production of PAF by PMN after 2 to 5 min of FT-1 incubation. FT 1 induced PAF release from PMN rather than accumulation. This PAF production was dependent on intra- and extracellular Ca 2+ . In this regard, the PAF receptor antagonists significantly blunted the ET-1-induced peak in cytosolic free Ca 2+ ([Ca 2+ ] i ). Our results, therefore, indicate that ET-1 is effective in causing aggregation of human PMN and that its action appears to be mediated by PAF production via a Ca 2+ -dependent mechanism.