Soslau G, McKenzie R J, Brodsky I, Devlin T M
Department of Biological Chemistry, Hahnemann University, Philadelphia, PA 19102, USA.
Biochim Biophys Acta. 1995 Jul 20;1268(1):73-80. doi: 10.1016/0167-4889(95)00051-s.
Our previous studies have demonstrated that platelets possess ATP purinergic receptors in addition to the ADP, P2T, receptor. Occupancy of the P2 receptor by ATP inhibited agonist-induced platelet aggregation. This study demonstrated that the mechanism of inhibition may involve ATP inhibition of agonist-induced mobilization of internal calcium. Within the cardiovascular system, the ATP inhibition of calcium mobilization is unique to platelets. All other cell types in the cardiovascular system, where calcium mobilization is affected by extracellular ATP, responded with an increased mobilization as opposed to inhibition. The platelet inhibitory response to ATP was enhanced by the addition of an ATP generating system, creatine phosphate/phosphocreatine kinase. ATP and ATP analogues were found to inhibit calcium mobilization with a rank order of alpha beta-methylene ATP, beta gamma-methylene ATP approximately ATP > benzoyl ATP > 2 methylthio ATP which is a characteristic of P2x-like receptors. The inhibitory effect of ATP could be abrogated by prolonged treatment of platelets with the P2x desensitizing agent, alpha beta-methylene ATP. Also, UTP and CTP were approximately as effective inhibitors as ATP while GTP was not. ATP competition with ADP for the P2T receptor was excluded in studies with platelets derived from an aspirin-treated individual which were essentially insensitive to ADP. The agonist-induced calcium mobilization and inhibition by ATP occurred with the thromboxane A2 mimetic, U46619, collagen and thrombin; however, the kinetics of mobilization varied somewhat with the different agonists. The responses to extracellular ATP were independent of extracellular Ca2+, where 1 mM calcium or 0.3 mM EGTA was added to the reaction mixture. The inhibition of calcium mobilization coupled to inhibition of platelet aggregation by extracellular ATP may serve an important physiologic role. ATP, released from activated platelets at localized sites of vascular injury, may help to limit the size of the platelet plug-clot that, if left unregulated, could occlude the injured blood vessel.
我们之前的研究表明，血小板除了具有ADP、P2T受体外，还拥有ATP嘌呤能受体。ATP占据P2受体可抑制激动剂诱导的血小板聚集。本研究表明，抑制机制可能涉及ATP对激动剂诱导的细胞内钙动员的抑制。在心血管系统中，ATP对钙动员的抑制是血小板所特有的。心血管系统中所有其他受细胞外ATP影响钙动员的细胞类型，其反应都是钙动员增加而非抑制。添加ATP生成系统磷酸肌酸/磷酸肌酸激酶可增强血小板对ATP的抑制反应。发现ATP和ATP类似物抑制钙动员的能力顺序为αβ-亚甲基ATP、βγ-亚甲基ATP≈ATP＞苯甲酰ATP＞2-甲硫基ATP，这是P2x样受体的特征。用P2x脱敏剂αβ-亚甲基ATP长期处理血小板可消除ATP的抑制作用。此外，UTP和CTP作为抑制剂的效果与ATP大致相同，而GTP则不然。在对来自阿司匹林治疗个体且对ADP基本不敏感的血小板进行的研究中，排除了ATP与ADP竞争P2T受体的可能性。激动剂诱导的钙动员以及ATP的抑制作用在血栓素A2模拟物U46619、胶原蛋白和凝血酶作用下均会发生；然而，不同激动剂作用下钙动员的动力学有所不同。细胞外ATP对细胞外钙的反应是独立的，反应混合物中添加了1 mM钙或0.3 mM乙二醇双四乙酸（EGTA）。细胞外ATP对钙动员的抑制与对血小板聚集的抑制可能具有重要的生理作用。在血管损伤的局部部位，活化血小板释放的ATP可能有助于限制血小板凝块的大小，否则若不受控制，血小板凝块可能会阻塞受损血管。
