Influence of nitric oxide on agonist-mediated calcium mobilization in platelets

Recent studies have characterized endothelium-derived relaxing factor as nitric oxide. It appears to exert its effect by elevating intracellular levels of cyclic GMP. In this study we confirm that nitric oxide is a potent inhibitor of agonist-induced irreversible aggregation. At the concentrations tested nitric oxide effectively blocked thrombin-stimulated mobilization of cytosolic-free calcium in Fura 2-loaded platelets. In addition, nitric oxide prevented the inositol 1,4,5-trisphosphate-stimulated calcium rise in cytosolic calcium in saponin-permeabilized Fura 2-loaded platelets. Similar to the action of adenylate cyclase stimulators, nitric oxide facilitated lowering of calcium levels raised by the action of agonists. The specific mechanism by which it exerts its effect on intracellular levels of calcium is not clear.