[Induction of human platelet Ca2+ fluxes by anti-GP IIb/IIIa and anti-CD9 monoclonal antibodies].

Calcium plays a central role in platelet activation. Calcium changes in acquorin-loaded human platelets induced by monoclonal antibodies (McAbs) were recorded using a PIGA-apparatus. McAb Apt4 is specific for GP IIb/IIIa and McAb XW-1 and SJ-9A4 are directed against CD9 antigen. All three McAbs were shown to elicit a Ca2+ rise in aequorin-loaded platelets. This rise was the sole result of Ca2+ influx in the case of Apt4 and XW-1 and of both Ca2+ influx and mobilization in the case of SJ-9A4. Platelet Ca2+ fluxes and aggregation induced by the three McAbs were inhibited by an anti-GP IIb/IIIa McAb HIP8. The Ca2+ channel blocker vorapamil exerted a complete inhibitory effect on platelet Ca2+ fluxes and aggregation induced by Apt4, and had a partial effect on that induced by XW-1 and SJ-9A4. The ADP inhibitor CP/CPK had a partial inhibitory effect on platelet Ca2+ fluxes and aggregation induced by Apt4 and XW-1, and a smal effect on that induced by SJ-9A4. The effects of the three McAbs were inhibited partially by the calmodulin inhibitor EBB. The results indicate that platelet Ca2+ fluxes induced by these three McAbs depend on different pathways.