CHARACTERIZATION OF P2X1 PURINORECEPTORS ON RAT PLATELETS - EFFECT OFCLOPIDOGREL

This study aimed to determine the binding characteristics of [H-3]alph a,beta-Me-ATP, a specific ligand of the P2x1 receptors to rat platelet s, and to investigate the effect of clopidogrel, a thienopyridine comp ound which has been found to selectively inhibit ADP-induced platelet aggregation and adenylyl cyclase ex vivo. Binding of [H-3]alpha,beta-M e-ATP to rat platelets was time-dependent and saturable, Scatchard ana lysis of the saturation binding data indicated that [H-3]alpha,beta-Me -ATP bound to one population of specific binding sites with high. affi nity (K-d=23.6 +/- 1.6 nM; B-max = 690 +/- 24 fmole/10(8)cells) (n=3). Unlabelled alpha,beta-Me-ATP as well as 2-MeS-ADP and ADP competitive ly inhibited the specific binding of [H-3]alpha,beta-Me-ATP with IC50 values of 19.0 +/- 6.6, 103 divided by/- 20 and 1120 +/- 80 nM respect ively (n=3). Other nucleotide analogues such as ATP. ATP-gamma S, UTP and GTP also antagonized [H-3]alpha,beta-Me-ATP binding. When administ ered orally (10mg/kg, p.o.), clopidogrel inhibited ADP- or 2-MeS-ADP-i nduced platelet aggregation but did not affect the binding of [H-3]alp ha,beta-Me-ATP to rat platelets ex vivo. In vitro, alpha,beta-Me-ATP d id not induce the aggregation or shape change of rat platelets and did not interfere with ADP-induced platelet aggregation.