Extended pharmacological profiles of rat P2Y2 and rat P2Y4 receptors and their sensitivity to extracellular H+ and Zn2+ ions

1 Two molecularly distinct rat P2Y receptors activated equally by adenosine-5'-triphosphate (ATP) and uridine-5'-triphosphate (UTP) (rP2Y(2) and rP2Y(4) receptors) were expressed in Xenopus oocytes and studied extensively to find ways to pharmacologically distinguish one from the other. 2 Both P2Y subtypes were activated fully by a number of nucleotides. Tested nucleotides were equipotent at rP2Y(4) (ATP = UTP = CTP = GTP = ITP), but not at rP2Y(2) (ATP = UTP>CTP>GTP>ITP). For dinucleotides (Ap(n)A, n=2-6), rP2Y(4) was only fully activated by Ap(4)A which was as potent as ATP. All tested dinucleotides, except for Ap(2)A, fully activated rP2Y(2), but none were as potent as ATP. ATPgammaS and BzATP fully activated rP2Y(2), whereas ATPgammaS was a weak agonist and BzATP was inactive (as an agonist) at rP2Y4 receptors. 3 Each P2Y subtype showed different sensitivities to known P2 receptor antagonists. For rP2Y(2), the potency order was suramin > > PPADS = RB-2 > TNP-ATP and suramin was a competitive antagonist (pA(2), 5.40). For rP2Y(4), the order was RB-2 > > suramin > PPADS > TNP-ATP and RB-2 was a competitive antagonist (pA(2), 6.43). Also, BzATP was an antagonist at rP2Y(4) receptors. 4 Extracellular acidification (from pH 8.0 to pH 5.5) enhanced the potency of ATP and UTP by 8-10-fold at rP2Y(4) but did not affect agonist responses at rP2Y(2) receptors. 5 Extracellular Zn2+ ions (0.1-300 muM) coapplied with ATP inhibited agonist responses at rP2Y(4) but not at rP2Y(2) receptors. 6 These two P2Y receptors differ significantly in terms of agonist and antagonist profiles, and the modulatory activities of extracellular H+ and Zn2+ ions. These pharmacological differences will help to distinguish between rP2Y(2) and rP2Y(4) receptors, in vivo.