A subtype-selective, competitive and reversible P2X1 receptor antagonist. Displays IC50 values of 0.21, 28.9, > 50 and > 100 μM for human P2X1, P2X3, P2X2, and P2X4-mediated responses respectively. Selective over adrenoceptors, histamine and P2Y receptors. Also selectively inhibits the α-subunit of Go/i (EC50 ~300 nM).