Influence of chemical pollution on brain adenosine receptors of Mugil cephalus

The aim of this study was to investigate adenosine receptor sites in whole brain membranes of the saltwater teleost fish, Mugil cephalus, using the A1 receptor selective agonist, [3H]- N6-cyclohexyladenosine ([3H]-CHA). Specific binding was saturable and reversible. A single class of high-affinity binding sites was identify, showing Kd and Bmax values of 1.43±0.26 nM and 69.5±5.4 fmol/mg protein, respectively. In competition experiments, the following adenosine analogues, CHA, (2-[p-(2-carboxyethyl)-phenylethylamino]-5′-N-ethylcarboxamidoadenosine) (CGS21680), 5′-(N-cyclopropyl)carboxamidoadenosina (CPCA) and N6-[2-(3,5-dimethoxyphenyl)-2-(2methylphenyl)-ethyl]adenosine (DPMA), displaced [3H]-CHA specifically bound to brain membranes, revealing that the high-affinity binding sites have some pharmacological properties of mammalian A1 adenosine receptors. Furthermore, our findings indicate that in captivity chemical pollution determines a decrease of the Kd value corresponding to a 5-fold increase in affinity, whereas it does not induce any variation of the receptor density.