title: Molecular mechanism of thromboxane A(2)-induced platelet aggregation. Essential role for p2t(ac) and alpha(2a) receptors.
abstract: Thromboxane A(2) is a positive feedback lipid mediator produced following platelet activation. The G(q)-coupled thromboxane A(2) receptor subtype, TPalpha, and G(i)-coupled TPbeta subtype have been shown in human platelets. ADP-induced platelet aggregation requires concomitant signaling from two P2 receptor subtypes, P2Y1 and P2T(AC), coupled to G(q) and G(i), respectively. We investigated whether the stable thromboxane A(2) mimetic, (15S)-hydroxy-9, 11-epoxymethanoprosta-5Z,13E-dienoic acid (U46619), also causes platelet aggregation by concomitant signaling through G(q) and G(i), through co-activation of TPalpha and TPbeta receptor subtypes. Here we report that secretion blockade with Ro 31-8220, a protein kinase C inhibitor, completely inhibited U46619-induced, but not ADP- or thrombin-induced, platelet aggregation. Ro 31-8220 had no effect on U46619-induced intracellular calcium mobilization or platelet shape change. Furthermore, U46619-induced intracellular calcium mobilization and shape change were unaffected by A3P5P, a P2Y1 receptor-selective antagonist, and/or cyproheptadine, a 5-hydroxytryptamine subtype 2A receptor antagonist. Either Ro 31-8220 or AR-C66096, a P2T(AC) receptor selective antagonist, abolished U46619-induced inhibition of adenylyl cyclase. In addition, AR-C66096 drastically inhibited U46619-mediated platelet aggregation, which was further inhibited by yohimbine, an alpha(2A)-adrenergic receptor antagonist. Furthermore, inhibition of U46619-induced platelet aggregation by Ro 31-8220 was relieved by activation of the G(i) pathway by selective activation of either the P2T(AC) receptor or the alpha(2A)-adrenergic receptor. We conclude that whereas thromboxane A(2) causes intracellular calcium mobilization and shape change independently, thromboxane A(2)-induced inhibition of adenylyl cyclase and platelet aggregation depends exclusively upon secretion of other agonists that stimulate G(i)-coupled receptors.
authors.affiliation: Department of Pharmacology, Temple University School of Medicine, Philadelphia, Pennsylvania 19140, USA.
authors.forename: B Z
authors.initials: BZ
authors.lastname: Paul
authors.forename: J
authors.initials: J
authors.lastname: Jin
authors.forename: S P
authors.initials: SP
authors.lastname: Kunapuli
mesh_terms: D019796:15-Hydroxy-11 alpha,9 alpha-(epoxymethano)prosta-5,13-dienoic Acid / Q000494:pharmacology; D000255:Adenosine Triphosphate / Q000031:analogs & derivatives / Q000494:pharmacology; D000262:Adenylyl Cyclases / Q000378:metabolism; D000317:Adrenergic alpha-Antagonists / Q000494:pharmacology; D002118:Calcium / Q000378:metabolism; D048429:Cell Size / Q000187:drug effects; D019204:GTP-Binding Proteins / Q000378:metabolism; D006801:Humans; D007211:Indoles / Q000494:pharmacology; D008565:Membrane Proteins; D010974:Platelet Aggregation / Q000187:drug effects*; D010975:Platelet Aggregation Inhibitors / Q000494:pharmacology; D018048:Receptors, Purinergic P2 / Q000378:metabolism*; D058472:Receptors, Purinergic P2Y1; D058925:Receptors, Purinergic P2Y12; D015398:Signal Transduction; D013928:Thromboxane A2 / Q000494:pharmacology*; D014662:Vasoconstrictor Agents / Q000494:pharmacology; D015016:Yohimbine / Q000494:pharmacology
chemical_list: C092108:2-propylthio-D-beta,gamma-difluoromethylene ATP; D000317:Adrenergic alpha-Antagonists; D007211:Indoles; D008565:Membrane Proteins; C546382:P2RY1 protein, human; C548576:P2RY12 protein, human; D010975:Platelet Aggregation Inhibitors; D018048:Receptors, Purinergic P2; D058472:Receptors, Purinergic P2Y1; D058925:Receptors, Purinergic P2Y12; D014662:Vasoconstrictor Agents; D015016:Yohimbine; D013928:Thromboxane A2; D019796:15-Hydroxy-11 alpha,9 alpha-(epoxymethano)prosta-5,13-dienoic Acid; D000255:Adenosine Triphosphate; D019204:GTP-Binding Proteins; D000262:Adenylyl Cyclases; D002118:Calcium; C064758:Ro 31-8220