ROLE OF P2Y1 PURINOCEPTOR IN ADP-INDUCED PLATELET ACTIVATION

ADP acts as an agonist of platelet aggregation via specific receptors which are still to be characterised, Amplification by PCR of a human p latelet cDNA library confirmed the presence of mRNA of the P2Y1 recept or in platelets, In order to determine if these P2Y1 receptors mere in volved in ADP-induced platelet activation, me determined the effects o f A3P5PS, an antagonist of the P2Y1 receptor, on the binding of [P-33] 2-MeS-ADP, a potent analogue of ADP, We found that A3P5PS displaced ab out 27% of [P-33]2-MeS-ADP binding, a receptor population which has be en shown to be resistant to treatment with clopidogrel, a selective an ti-ADP agent, A3P5PS specifically inhibited 2-MeS-ADP-induced shape ch ange and calcium increase but did not affect adenylyl cyclase down-reg ulation, 2-MeS-ADP-induced platelet aggregation was also inhibited by A3P5PS but was restored when platelets were further activated by serot onin, a non-aggregating compound, therefore suggesting that P2Y1-media ted stimulation is an absolute prerequisite for ADP to induce platelet aggregation and a key event for platelet activation and aggregation t o occur, These results therefore show that ADP-induced aggregation can not be attributed to activation of P2Y1 alone, but must be attributed to the simultaneous activation of the high affinity receptor (P2Y1) an d a low affinity receptor of ADP (still to be discovered), each of the m essential, but neither able to trigger aggregation alone. (C) 1998 F ederation of European Biochemical Societies.