Hypoxia or inflammation, activates the release of extracellular nucleotides such as ATP and UTP which interact with cell surface P2Y receptors to produce a broad range of physiological responses including cardiac function, platelet aggregation and smooth muscle cell proliferation. Eight mammalian P2Y receptors, members of G-protein coupled receptors, have been identified on the basis of sequence homology and pharmacological profile: the P2Y1, P2Y2, P2Y4, P2Y6, P2Y11, P2Y12, P2Y13 and P2Y14.