Prostacyclin and other related compounds known to increase intracellular cAMP levels inhibit platelet responses. The mechanisms involved are only partially known, especially those concerning the complex relations between Ca2+ and cAMP as opposite intracellular mediators. Here, we have investigated aggregation and secretion in quin2-loaded platelets under conditions in which Ca2+ and cAMP are the only intracellular mediators. Our results show that cAMP inhibits aggregation and secretion in ionophore-treated cell without modifying their intracellular Ca2+ levels. This result suggests that the inhibition takes place on some intracellular target for Ca2+.
