Potent purinergic receptor antagonist that displays high selectivity for P2X1 (IC50 values are 0.28, 0.69, 120, 1820, 47000 and > 300000 nM for rP2X1, rP2X1+5, rP2X2+3, rP2X3, rP2X2 and P2X4 receptors respectively). Provides antithrombotic protection in vivo. Also acts as a Gsα-selective antagonist.