Characterization of adenosine receptors in Mullus surmuletus

Abstract The intent of the present study was to investigate adenosine receptor sites in brain membranes of the saltwater teleost fish, Mullus surmuletus , using the A 1 receptor selective agonist, [ 3 H]CHA, and A 2a receptor selective agonist [ 3 H]CGS 21680. The A 1 selective agonist, [ 3 H]CHA, bound saturably, reversibly and with high affinity to a single-class of binding sites (K d 1.47 nM; B max 100–190 fmol/mg protein, dependent on fish length). The A 2a selective agonist, [ 3 H]CGS 21680, also bound saturably, reversibly and with relative high affinity to a single-class of binding sites (K d 44.2 nM; B max 150–300 fmol/mg protein dependent on fish length). In equilibrium competition experiments, adenosine analogous, NECA, CGS 21680, CHA, CPA, S-PIA, R-PIA, CPCA, DPMA, and xanthine antagonists, DPCPX, XAC, and THEO all displaced [ 3 H]CHA and [ 3 H]CGS 21680 specifically bound to brain membranes from Mullus surmuletus . Specific binding of both [ 3 H]CHA and [ 3 H]CGS 21680 was inhibited by GDPβS. For [ 3 H]CHA the IC 50 value was 2.5 ± 0.1 μ M, while for [ 3 H]CGS 21680 the IC 50 value was 7.7 ± 0.3 μ M. Our results indicate that the high affinity binding sites for [ 3 H]CHA have some pharmacological characteristics of mammalian A 1 adenosine receptors, while the binding sites for [ 3 H]CGS 21680 appear to be virtually identical to the binding sites for [ 3 H]CHA.