INTERACTION OF PROSTAGLANDINS WITH ADENOSINE-DIPHOSPHATE INDUCED INCREASE IN CYTOSOLIC FREE CALCIUM IN HUMAN PLATELETS

The interaction of prostaglandins with changes in cytosolic Ca2+ concentration ([Ca2+]) and aggregation of human platelets induced by adenosine diphosphate (ADP) were investigated. Cytosolic [Ca2+] was measured with the fluorescent dye Quin2. Addition of ADP (0.25-2.5-mu-mol l-1) to platelet suspensions produced a dose dependent increase in cytosolic [Ca2+] from a basal level of 51 +/- 1 nmol l-1 to maximum levels exceeding 1-mu-mol l-1 and induced platelet aggregation. Chelation of extracellular calcium with 100-mu-mol l-1 EGTA markedly reduced the increase in cytosolic [Ca2+] induced by 0.25-mu-mol l-1 ADP, while pretreatment with the calcium entry blocker verapamil was without effect. Stimulation of cyclic AMP with prostaglandins (PGD2, PGE1, PGE2, PGI2, but not PGF2-alpha) and forskolin, OT incubation with dibutyryl-cAMP, inhibited the rise in cytosolic [Ca2+] and platelet aggregation following ADP. We conclude that prostaglandins inhibit the increase in cytosolic [Ca2+] and aggregation of human platelets induced by ADP, probably by stimulation of cyclic AMP generation, thereby opposing the mechanism by which ADP increases cytostolic [Ca2+] and subsequently induces platelet aggregation.