Direct measurement of nitric oxide production in platelets: relationship with cytosolic Ca2+ concentration.

NO production in platelets has been followed by electrochemical detection. It was undetectable in unstimulated platelets and in thrombin or ADP-stimulated platelets, but dose-dependently stimulated by collagen. A production of 5 10(-19) mol/platelet was reached with 9 micrograms collagen. In collagen-stimulated platelets, preincubation with 1 mM L-Arg, D-Arg or L-NMMA increased by 77%, left unchanged or decreased by 63% NO production, respectively. NO production did not parallel cytosolic Ca2+ changes, although it decreased in low Ca2+ medium or when Ca2+ transients were attenuated by intracellular Ca2+ buffer. These results confirm that human platelets can generate NO. They demonstrate that cytosolic [Ca2+], although participating in the regulation of its synthesis, is not the messenger for NO synthase activation. Platelet NO production could become functionally important when collagen fibrils of the sub-endothelium are accessible.