Cyclic nucleotides modulate store-mediated calcium entry through the activation of protein-tyrosine phosphatases and altered actin polymerization in human platelets.
Agonists elevate the cytosolic calcium concentration in human platelets via a receptor-operated mechanism, involving both Ca(2+) release from intracellular stores and subsequent Ca(2+) entry, which can be inhibited by platelet inhibitors, such as prostaglandin E(1) and nitroprusside which elevate cAMP and cGMP, respectively. In the present study we investigated the mechanisms by which cAMP and cGMP modulate store-mediated Ca(2+) entry. Both prostaglandin E(1) and sodium nitroprusside inhibited thapsigargin-evoked store-mediated Ca(2+) entry and actin polymerization. However, addition of these agents after induction of store-mediated Ca(2+) entry did not affect either Ca(2+) entry or actin polymerization. Furthermore, prostaglandin E(1) and sodium nitroprusside dramatically inhibited the tyrosine phosphorylation induced by depletion of the internal Ca(2+) stores or agonist stimulation without affecting the activation of Ras or the Ras-activated phosphatidylinositol 3-kinase or extracellular signal-related kinase (ERK) pathways. Inhibition of cyclic nucleotide-dependent protein kinases prevented inhibition of agonist-evoked Ca(2+) release but it did not have any effect on the inhibition of Ca(2+) entry or actin polymerization. Phenylarsine oxide and vanadate, inhibitors of protein-tyrosine phosphatases prevented the inhibitory effects of the cGMP and cAMP elevating agents on Ca(2+) entry and actin polymerization. These results suggest that Ca(2+) entry in human platelets is directly down-regulated by cGMP and cAMP by a mechanism involving the inhibition of cytoskeletal reorganization via the activation of protein tyrosine phosphatases.
Department of Physiology, University of Cambridge, Downing Street, Cambridge CB2 3EG, United Kingdom.
J A
JA
Rosado
T
T
Porras
M
M
Conde
S O
SO
Sage
D000199:Actins / Q000097:blood* / Q000737:chemistry; D000244:Adenosine Diphosphate / Q000494:pharmacology; D000527:Alprostadil / Q000494:pharmacology; D001152:Arsenicals / Q000494:pharmacology; D001792:Blood Platelets / Q000187:drug effects / Q000502:physiology*; D002118:Calcium / Q000097:blood*; D002227:Carbazoles; D000242:Cyclic AMP / Q000097:blood*; D006152:Cyclic GMP / Q000097:blood*; D004533:Egtazic Acid / Q000494:pharmacology; D004789:Enzyme Activation; D004791:Enzyme Inhibitors / Q000494:pharmacology; D006801:Humans; D066298:In Vitro Techniques; D007211:Indoles / Q000494:pharmacology; D019950:Mitogen-Activated Protein Kinase 1 / Q000097:blood; D048052:Mitogen-Activated Protein Kinase 3; D020928:Mitogen-Activated Protein Kinases / Q000097:blood*; D009599:Nitroprusside / Q000494:pharmacology; D010766:Phosphorylation; D015539:Platelet Activation / Q000187:drug effects / Q000502:physiology; D010975:Platelet Aggregation Inhibitors / Q000494:pharmacology*; D017027:Protein Tyrosine Phosphatases / Q000037:antagonists & inhibitors / Q000097:blood*; D011758:Pyrroles / Q000494:pharmacology; D019284:Thapsigargin / Q000494:pharmacology; D013917:Thrombin / Q000494:pharmacology; D014638:Vanadates / Q000494:pharmacology
D000199:Actins; D001152:Arsenicals; D002227:Carbazoles; D004791:Enzyme Inhibitors; D007211:Indoles; D010975:Platelet Aggregation Inhibitors; D011758:Pyrroles; C029341:oxophenylarsine; D009599:Nitroprusside; D014638:Vanadates; D004533:Egtazic Acid; C057416:KT 5720; D000244:Adenosine Diphosphate; D019284:Thapsigargin; D000242:Cyclic AMP; D019950:Mitogen-Activated Protein Kinase 1; D048052:Mitogen-Activated Protein Kinase 3; D020928:Mitogen-Activated Protein Kinases; D017027:Protein Tyrosine Phosphatases; D013917:Thrombin; D000527:Alprostadil; D006152:Cyclic GMP; D002118:Calcium