Role of protein kinase C in U46619-induced platelet shape change, aggregation and secretion

Stimulation of rat platelets with U46619 induced Ca2+ mobilization and platelet shape change, but aggregation and secretion were induced when platelets were stimulated with U46619 plus phorbol 12-myristate 13-acetate (PMA). However, stimulation of rabbit platelets with U46619 induced all the three platelet responses. Aggregation and secretion of rabbit platelets were enhanced by simultaneous addition of PMA and inhibited by staurosporine, but platelet shape change was not affected by them. These results suggest that protein kinase C is important for aggregation and secretion, but not for platelet shape change. On the other hand, pretreatment of platelets with PMA inhibited platelet shape change as well as Ca2+ mobilization and inositol phosphate formation, indicating that the shape change was mediated by PMA-sensitive mechanism which was not clarified.