RT Journal Article
SR Electronic
T1 Thrombin-stimulated phospholipase C activity is inhibited without visible delay by a rapid increase in the cyclic GMP levels induced by sodium nitroprusside.
JF Molecular Pharmacology
JO Mol Pharmacol
FD American Society for Pharmacology and Experimental Therapeutics
SP 367
OP 379
VO 50
IS 2
A1 F J Azula
A1 E S Alzola
A1 M Conde
A1 M Trueba
A1 J M Macarulla
A1 A Marino
YR 1996
UL http://molpharm.aspetjournals.org/content/50/2/367.abstract
AB Different drugs that elevate the cGMP levels inhibit the agonist-induced platelet activation. The mechanisms of action of cGMP probably include inhibition of both phospholipase C and the increase in intracellular Ca2+ concentration, and these effects seem to be mediated by cGMP-dependent protein kinases. However, in most studies, cells were preincubated with nitrovasodilators before stimulation. The effect of the preincubation with sodium nitroprusside before stimulation or the simultaneous addition of sodium nitroprusside and thrombin has been compared. The simultaneous addition of sodium nitroprusside and thrombin was able to inhibit without any significant delay the platelet aggregation. This rapid effect was correlated with an inhibition of both the maximum increase in intracellular Ca2+ concentration and the phospholipase C activity. Also, the simultaneous addition of sodium nitroprusside and thrombin clearly accelerated the decline in the Ca2+ signal, which was not observed in platelets preincubated with sodium nitroprusside. The rapid inhibition induced by sodium nitroprusside was correlated with a rapid and significant increase in the cGMP levels and reversed when platelets were pretreated with methylene blue. The inhibitor of cAMP-dependent protein kinase Rp-8-(4-chlorophenylthio)-adenosine-3',5'-cyclic monophosphorothioate was able to abolish nearly completely the inhibitory effect induced by sodium nitroprusside independent of the protocol used. Thus, the rapid inhibition induced by sodium nitroprusside seems to be induced by a rapid phosphorylation-dependent mechanism. In addition, both cGMP- and cAMP-dependent protein kinase seem to be involved; however, the cAMP-dependent protein kinase seems to be more important.