Nitroprusside differentially inhibits ADP-stimulated calcium influx and mobilization in human platelets.
1. The effect of nitroprusside on cGMP concn., cAMP concn., shape change, aggregation, intracellular free Ca2+ concn. (by quin-2 fluorescence) and Mn2+ entry (by quenching of quin-2) was investigated in human platelets incubated with 1 mM-Ca2+ or 1 mM-EGTA. 2. Nitroprusside (10 nM-10 microM) caused similar concentration-dependent increases in platelet cGMP concn. and was without effect on cAMP concn. in the presence of extracellular Ca2+ or EGTA. 3. In ADP (3-6 microM)-stimulated platelets, nitroprusside caused 50% inhibition of shape change at 0.4 microM (+Ca2+) or 1.3 microM (+EGTA), aggregation at 0.09 microM (+Ca2+) and of increased intracellular Ca2+ at 0.02 microM (+Ca2+) or 2.1 microM (+EGTA). Entry of 1 mM-Mn2+ (-Ca2+) was inhibited by 80% by 5 microM-nitroprusside. 4. In ionomycin (20-500 nM)-stimulated platelets, nitroprusside (10 nM-100 microM) did not inhibit shape change or intracellular-Ca2+-increase responses, and only partially inhibited aggregation. 5. In phorbol myristate acetate (10 nM)-stimulated platelets, neither shape change nor aggregation was inhibited by 5 microM-nitroprusside. 6. The data demonstrate that nitroprusside inhibits ADP-mediated Ca2+ influx more potently than Ca2+ mobilization. Nitroprusside appears not to influence Ca2+ efflux or sequestration and not to affect the sensitivity of the activation mechanism to intracellular Ca2+ concn. or activation of protein kinase C.
Morgan
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Department of Cardiology, University of Wales College of Medicine, Heath Park, Cardiff, U.K.
Newby
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D000244:Adenosine Diphosphate / Q000378:metabolism*; D001665:Binding Sites; D001792:Blood Platelets / Q000187:drug effects* / Q000378:metabolism; D002118:Calcium / Q000097:blood*; D006152:Cyclic GMP / Q000378:metabolism; D004987:Ethers / Q000494:pharmacology; D005260:Female; D005292:Ferricyanides / Q000494:pharmacology*; D006801:Humans; D015759:Ionomycin; D007476:Ionophores / Q000494:pharmacology; D008297:Male; D009599:Nitroprusside / Q000494:pharmacology*; D013755:Tetradecanoylphorbol Acetate / Q000494:pharmacology
D004987:Ethers; D005292:Ferricyanides; D007476:Ionophores; D009599:Nitroprusside; D015759:Ionomycin; D000244:Adenosine Diphosphate; D006152:Cyclic GMP; D013755:Tetradecanoylphorbol Acetate; D002118:Calcium