title: Role of cGMP and cGMP-dependent protein kinase in nitrovasodilator inhibition of agonist-evoked calcium elevation in human platelets.
abstract: Most platelet agonists activate and elevate the cytosolic free calcium concentration in human platelets through receptor-dependent mechanisms that are antagonized by cAMP- and cGMP-elevating agents. Nitrovasodilators such as nitroprusside and endothelium-derived relaxing factor are potent cGMP-elevating platelet inhibitors. In the present study, the role of cGMP and cGMP-dependent protein kinase in nitrovasodilator inhibition of ADP- and thrombin-evoked calcium elevation and activation of human platelets was investigated. Preincubation of platelets with 8-(4-chlorophenylthio)guanosine 3',5'-cyclic monophosphate (8-pCPT-cGMP; a membrane-permeant selective activator of the cGMP-dependent protein kinase that does not significantly affect cGMP-regulated phosphodiesterases) inhibited the thrombin-induced phosphorylation mediated by myosin light chain kinase and protein kinase C. Nitrovasodilator-induced protein phosphorylation in human platelets was distinct from that induced by cAMP-elevating prostaglandins and could be mimicked by 8-pCPT-cGMP. Preincubation of human platelets with nitrovasodilators or 8-pCPT-cGMP inhibited the ADP- and thrombin-evoked calcium elevation in the presence and absence of external calcium. Nitrovasodilators and 8-pCPT-cGMP also inhibited the agonist-induced Mn2+ influx, but stopped-flow experiments indicated that the ADP receptor-operated cation channel was not significantly inhibited. These results suggest that in human platelets nitrovasodilators inhibit the agonist-induced calcium mobilization from intracellular stores and the secondary store-related calcium influx but not the ADP receptor-operated cation channel. The results also suggest that these nitrovasodilator effects are mediated by cGMP and the cGMP-dependent protein kinase.
authors.affiliation: Medizinische Universitätsklinik, Klinische Forschergruppe, Würzburg, Federal Republic of Germany.
authors.forename: J
authors.initials: J
authors.lastname: Geiger
authors.forename: C
authors.initials: C
authors.lastname: Nolte
authors.forename: E
authors.initials: E
authors.lastname: Butt
authors.forename: S O
authors.initials: SO
authors.lastname: Sage
authors.forename: U
authors.initials: U
authors.lastname: Walter
mesh_terms: D000244:Adenosine Diphosphate / Q000494:pharmacology; D000527:Alprostadil / Q000494:pharmacology*; D001792:Blood Platelets / Q000187:drug effects* / Q000378:metabolism; D002118:Calcium / Q000378:metabolism*; D002451:Cell Compartmentation; D006152:Cyclic GMP / Q000502:physiology*; D003593:Cytoplasm / Q000378:metabolism; D006801:Humans; D066298:In Vitro Techniques; D015640:Ion Channel Gating; D007700:Kinetics; D008981:Molsidomine / Q000031:analogs & derivatives* / Q000494:pharmacology; D009599:Nitroprusside / Q000494:pharmacology*; D010750:Phosphoproteins / Q000378:metabolism; D011494:Protein Kinases / Q000502:physiology*; D011956:Receptors, Cell Surface / Q000502:physiology; D013917:Thrombin / Q000494:pharmacology; D014665:Vasodilator Agents / Q000494:pharmacology*
chemical_list: D010750:Phosphoproteins; D011956:Receptors, Cell Surface; D014665:Vasodilator Agents; D009599:Nitroprusside; C002385:linsidomine; D000244:Adenosine Diphosphate; D008981:Molsidomine; D011494:Protein Kinases; D013917:Thrombin; D000527:Alprostadil; D006152:Cyclic GMP; D002118:Calcium