Soslau G, Brodsky I, Parker J
Department of Biochemistry, Hahnemann University School of Medicine, Philadelphia, PA 19102-1192.
Biochim Biophys Acta. 1993 Jun 6;1177(2):199-207. doi: 10.1016/0167-4889(93)90041-m.
This report demonstrates that platelets possess P2 purinoceptors with unique properties that distinguish them from the ADP (P2T) receptor. Extracellular ATP, and its poorly hydrolyzable analogues, inhibit collagen- and U46619 (a thromboxane mimetic)-induced platelet aggregations. Adenosine deaminase was without effect on ATP action while reversing the inhibitory effect of adenosine. A unique aspect of the P2 receptor is the sensitivity to UTP and CTP and insensitivity to GTP. The rank order of inhibition by beta gamma-methylene ATP, alpha beta-methylene ATP > ATP indicates that a P2x-like receptor is present on the platelet membrane. This conclusion is further supported by the nearly complete desensitization to ATP by pre-exposure of platelets to alpha beta-methylene-ATP. However, unlike previously described P2x purinoceptors, the inhibition of platelet aggregation by extracellular ATP appears to result, at least in part, from the ATP-induced increase of intracellular cyclic AMP levels apparently coupled through a Gs protein. The combined addition of iloprost (0.14 to 1.39 nM) and ATP (18 microM) or ATP (20-40 microM) and the phosphodiesterase inhibitor theophylline (0.5 to 1 mM) synergistically inhibited platelet aggregation implying a common interactive site with adenylate cyclase. This is further substantiated by the ability of the adenylate cyclase inhibitor, 2',5'-dideoxyadenosine, to abrogate the inhibitory effects of ATP. The protein kinase A (PKA) inhibitor H1004 blocks ATP inhibition of platelet aggregation while the protein kinase C inhibitor H7 did not. This implies that the generation of cyclic AMP, with the subsequent activation of PKA and phosphorylation of selected proteins is required, in part, for the action of ATP.
本报告表明，血小板具有P2嘌呤受体，其独特性质使其有别于ADP（P2T）受体。细胞外ATP及其水解缓慢的类似物可抑制胶原和U46619（一种血栓素类似物）诱导的血小板聚集。腺苷脱氨酶对ATP的作用无影响，但可逆转腺苷的抑制作用。P2受体的一个独特之处在于其对UTP和CTP敏感，而对GTP不敏感。βγ-亚甲基ATP、αβ-亚甲基ATP＞ATP的抑制作用强度顺序表明血小板膜上存在类似P2x的受体。血小板预先暴露于αβ-亚甲基-ATP后对ATP几乎完全脱敏，这进一步支持了该结论。然而，与先前描述的P2x嘌呤受体不同，细胞外ATP对血小板聚集的抑制作用似乎至少部分是由于ATP诱导细胞内环状AMP水平升高，这显然是通过Gs蛋白偶联实现的。联合添加伊洛前列素（0.14至1.39 nM）和ATP（18 μM）或ATP（20 - 40 μM）与磷酸二酯酶抑制剂茶碱（0.5至1 mM）可协同抑制血小板聚集，这意味着它们与腺苷酸环化酶有共同的相互作用位点。腺苷酸环化酶抑制剂2',5'-二脱氧腺苷能够消除ATP的抑制作用，这进一步证实了这一点。蛋白激酶A（PKA）抑制剂H1004可阻断ATP对血小板聚集的抑制作用，而蛋白激酶C抑制剂H7则无此作用。这意味着环状AMP的生成以及随后PKA的激活和特定蛋白质的磷酸化在ATP的作用中部分是必需的。
