Dangelmaier C, Jin J, Smith J B, Kunapuli S P
Department of Pharmacology, Temple University Medical School, Philadelphia, PA, USA.
Thromb Haemost. 2001 Feb;85(2):341-8.
Platelet activation results in shape change, aggregation, generation of thromboxane A2, and release of granule contents. We have recently demonstrated that secreted ADP is essential for thromboxane A2-induced platelet aggregation (J. Biol. Chem. 274: 29108-29114, 1999). The aim of this study was to investigate the role of secreted ADP interacting at P2 receptor subtypes in platelet secretion. Platelet secretion induced by the thromboxane A2 mimetic U46619 was unaffected by adenosine-3'phosphate-5'-phosphate, a P2Y1 receptor selective antagonist. However, AR-C66096, a selective antagonist of the P2T(AC) receptor, inhibited U46619-induced platelet secretion, indicating an important role for Gi signaling in platelet secretion. Selective activation of either the P2T(AC) receptor or the alpha2A adrenergic receptor did not cause platelet secretion, but potentiated U46619-induced platelet secretion. SC57101, a fibrinogen receptor antagonist, failed to inhibit platelet secretion, demonstrating that outside-in signaling was not required for platelet secretion. Since Gi signaling results in reduction of basal cAMP levels through inhibition of adenylyl cyclase, we investigated whether this is the signaling event that potentiates platelet secretion. SQ22536 or dideoxyadenosine, inhibitors of adenylyl cyclase, failed to potentiate U46619-induced primary platelet secretion, indicating that reduction in cAMP levels does not directly contribute to platelet secretion. Wortmannin, a selective inhibitor of PI-3 kinase, minimally inhibited U46619-induced platelet secretion when it was solely mediated by Gq, but dramatically ablated the potentiation of Gi signaling. We conclude that signaling through the P2T(AC) receptor by secreted ADP causes positive feedback on platelet secretion through a PI-3 kinase pathway.
血小板活化会导致其形态改变、聚集、血栓素A2的生成以及颗粒内容物的释放。我们最近证明，分泌的ADP对于血栓素A2诱导的血小板聚集至关重要（《生物化学杂志》274: 29108 - 29114, 1999）。本研究的目的是探讨分泌的ADP在P2受体亚型上相互作用在血小板分泌中的作用。血栓素A2模拟物U46619诱导的血小板分泌不受P2Y1受体选择性拮抗剂3'-磷酸-5'-磷酸腺苷的影响。然而，P2T(AC)受体的选择性拮抗剂AR - C66096抑制了U46619诱导的血小板分泌，表明Gi信号在血小板分泌中起重要作用。选择性激活P2T(AC)受体或α2A肾上腺素能受体均未引起血小板分泌，但增强了U46619诱导的血小板分泌。纤维蛋白原受体拮抗剂SC57101未能抑制血小板分泌，表明血小板分泌不需要外向内信号传导。由于Gi信号通过抑制腺苷酸环化酶导致基础cAMP水平降低，我们研究了这是否是增强血小板分泌的信号事件。腺苷酸环化酶抑制剂SQ22536或双脱氧腺苷未能增强U46619诱导的初级血小板分泌，表明cAMP水平降低并不直接促进血小板分泌。渥曼青霉素是一种PI - 3激酶的选择性抑制剂，当U46619诱导的血小板分泌仅由Gq介导时，它对其抑制作用最小，但显著消除了Gi信号的增强作用。我们得出结论，分泌的ADP通过P2T(AC)受体发出的信号通过PI - 3激酶途径对血小板分泌产生正反馈作用。
