Activity of novel adenine nucleotide derivatives as agonists and antagonists at recombinant rat P2X receptors

The effects of structural modifications of adenine nucleotides previously s hown to enhance either agonist (2-thioether groups) or antagonist (addition al phosphate moieties at the 3'- or 2'-position) properties at P2Y(1) recep tors were examined at recombinant rat P2X(1), P2X(2), P2X(3), and P2X(4) re ceptors exp pressed in Xenopus oocytes. The potency of P2Y(1) agonists HT-A MP (2-(hexylthio)adenosine-5'-monophosphate) and PAPET (2-[2-(4-aminophenyl )ethylthio]adenosine was examined at P2X receptors. Both nucleotides showed a preference for the Group I (alpha,beta-meATP-sensitive, fast-inactivatin g) P2X subunits. HT-AMP was 5-fold more potent than ATP at P2X(3) receptors and a partial agonist at all except P2X(2) receptors, at which it was a fu ll agonist. The efficacy of HT-AMP was as low as 23% at P2X(4) receptors. P APET was a weak partial agonist at rat P2X(4) receptors and a nearly full a gonist at the other subtypes. At rat P2X(3) receptors, PAPET was more poten t than any other known agonist (EC50 = 17 +/- 3 nM). MRS 2179 (N-6- methyl- 2'-deoxyadenosine 3', 5-bisphosphate, a potent P2Y(1) receptor antagonist) inhibited ATP-evoked responses at rat P2X(1) receptors with an IC50 value o f 1.15 +/- 0.21 mu M. MRS 2179 was a weak antagonist at rat P2X(3) receptor s, with an IC50 value of 12.9 +/- 0.1 mu M, and was inactive at rat P2X(2) and P2X(4) receptors. Thus, MRS 2179 was 11-fold and 130-fold selective for P2Y(1) receptors vs. P2X(1) and P2X(3) receptors, respectively. MRS 2209, the corresponding 3'-deoxy-2'-phosphate isomer, was inactive at rat P2X(1) receptors, thus demonstrating its greater selectivity as a P2Y(1) receptor antagonist. Various adenine bisphosphates in the family of MRS 2179 contain ing modifications of either the adenine (P2Y(1) antagonists with 2- and 6-s ubstitutions), the phosphate (a 3',5'-cyclic diphosphate, inactive at P2Y(1 ) receptors), or the ribose moieties (antagonist carbocyclic analogue), wer e inactive at both rat P2X(1) and P2X(3) receptors. An anhydrohexitol deriv ative (MRS 2269) and an acyclic derivative (MRS 2286), proved to be selecti ve antagonists at P2Y(1) receptors, since they were inactive as agonist or antagonist at P2X(1) and P2X(3) receptors. Published 2000 Wiley-Liss, Inc.d agger