Influence of Bay k 8644 on aequorin-loaded human platelets.

In aequorin-loaded human platelets, Bay k 8644 (1-100 microM) had no effect on the resting level of cytoplasmic Ca2+ and did not induce aggregation by itself. Though the rise of cytoplasmic Ca2+ and platelet aggregation induced by thrombin (0.1 U/ml) also was not inhibited by 1-10 microM of Bay k 8644, at concentration of 3-10 microM, it dose-dependently reduced those induced by collagen (5 micrograms/ml). The present study shows that human platelets do not have dihydropyridine sensitive Ca channels.