The novel heteromeric bivalent ligand SB9 potently antagonizes P2Y(1) receptor-mediated responses

Effects of 6-[(4,6,8-trisulfo-1-naphthyl)iminocarbonyl-1,3-(4-methylphenyle ne)iminocarbonyl-1,3-phenylene-azo]-pyridoxal-5'-phosphate (SB9), a heterod imeric bivalent ligand consisting of pyridoxal-5'-phosphate and the suramin monomer, were studied on contractions of the rat vas deferens elicited by alpha beta-methylene ATP (alpha beta meATP; mediated by P2X(1)-like recepto rs), contractions of the guinea-pig ileal longitudinal smooth muscle elicit ed by adenosine 5'-O-(2-thiodiphosphate) (ADP beta S; mediated by P2Y(1)-li ke receptors), and the degradation of ATP by ecto-nucleotidases in follicul ated Xenopus laevis oocytes. SB9 (0.1-10 mu M) antagonized contractile resp onses produced by alpha beta meATP or ADP beta S in a concentration-depende nt manner. Schild analysis yielded linear regression lines of unit slope, i ndicating competitive antagonism. From the rightward shifts of the agonist concentration-response curves pA(2) values of 6.05+/-0.13 (vas deferens) an d 6.98+/-0.07 (ileum) were derived. In both preparations, SB9 behaved as a slow onset, slow offset antagonist. Incubation of three oocytes in the pres ence of ATP produced an increase in inorganic phosphate (P-i) over a 30-min period, which amounted to 35.1+/-1.9 mu M P-i from 100 mu M ATP. SB9 (10-1 000 mu M) reduced this degradation (pIC(50) = 4.33+/-0.10). The results ill ustrate that SB9 is a high-affinity P2Y(1) receptor antagonist with a remar kable selectivity for P2Y(1) vs. P2X(1) receptors (about 10-fold) and ecto- nucleotidases (447-fold). These properties make it unique among the pyridox al-5'-phosphate and suramin derivatives reported to date. (C) 2000 Publishe d by Elsevier Science B.V. All rights reserved.