Potent purinergic receptor antagonist that displays high selectivity for P2X 1 (IC 50 values are 0.28, 0.69, 120, 1820, 47000 and > 300000 nM for rP2X 1 , rP2X 1+5 , rP2X 2+3 , rP2X 3 , rP2X 2 and P2X 4 receptors respectively). Provides antithrombotic protection in vivo . Also acts as a G s α -selective antagonist.