Interaction of prostaglandins with adenosine diphosphate induced increase in cytosolic free calcium in human platelets

Abstract

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 μmol 1⁻¹) to platelet suspensions produced a dose dependent increase in cytosolic [Ca²⁺] from a basal level of 51 ± 1 nmol 1⁻¹ to maximum levels exceeding 1 μmol 1⁻¹ and induced platelet aggregation. Chelation of extracellular calcium with 100 μmol 1⁻¹ EGTA markedly reduced the increase in cytosolic [Ca²⁺] induced by 0.25 μmol 1⁻¹ ADP, while pretreatment with the calcium entry blocker verapamil was without effect. Stimulation of cyclic AMP with prostaglandins (PGD₂, PGE₁, PGE₂, PGI₂, but not PGF_2α) and forskolin, or 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.

Key Words:

• adenosine diphosphate
• calcium blockade
• cyclic AMP
• cytosolic calcium
• forskolin
• human platelets
• platelet aggregation
• prostaglandins
• Quin2