Nitric oxide and platelet energy metabolism.

This study was undertaken to determine whether nitric oxide (NO) can affect platelet responses through the inhibition of energy production. It was found that NO donors: S-nitroso-N-acetylpenicyllamine, SNAP, (5-50 μM) and sodium nitroprusside, SNP, (5-100 μM) inhibited collagen- and ADP-induced aggregation of porcine platelets. The corresponding IC50 values for SNAP and SNP varied from 5 to 30 μM and from 9 to 75 μM, respectively. Collagen- and thrombin-induced platelet secretion was inhibited by SNAP (IC50 = 50 μM) and by SNP (IC50 = 100 μM). SNAP (20-100 μM), SNP (10-200 μM) and collagen (20 μg/ml) stimulated glycolysis in intact platelets. The degree of glycolysis stimulation exerted by NO donors was similar to that produced by respiratory chain inhibitors (cyanide and antimycin A) or uncouplers (2,4-dinitrophenol). Neither the NO donors nor the respiratory chain blockers affected glycolysis in platelet homogenate. SNAP (20-100 μM) and SNP (50-200 μM) inhibited oxygen consumption by platelets. The effect of SNP and SNAP on glycolysis and respiration was not reduced by 1H-[1,2,4]oxadiazolo-[4,3-a]quinoxalin-1-one, a selective inhibitor of NO-stimulated guanylate cyclase. SNAP (5-100 μM) and SNP (10-300 μM) inhibited the activity of platelet cytochrome oxidase and had no effect on NADH:ubiquinone oxidoreductase and succinate dehydrogenase. Blocking of the mitochondrial energy production by antimycin A slightly affected collagen-evoked aggregation and strongly inhibited platelet secretion. The results indicate that: 1) in porcine platelets NO is able to diminish mitochondrial energy production through the inhibition of cytochrome oxidase, 2) the inhibitory effect of NO on platelet secretion (but not aggregation) can be attributed to the reduction of mitochondrial energy production