Characterization of A 1 adenosine receptors in membranes from whole goldfish brain

Abstract

1. 1. A 1 adenosine receptor binding was investigated using the selective agonist [ 3H]-cyclohexl-adenosine ([ 3H]CHA) on membranes prepared from adult (12–14 cm length) goldfish whole brain. 2. 2. The A 1 receptor agonist [ 3H]-cyclohexyladenosine bound saturably, reversibly and with high affinity ( K d = 1.20 ± 0.08 nM; B max = 6.8 ± 3.02 fmol/mg protein). 3. 3. The specific binding was increased by Mg 2+ and inhibited by guanosine 5′-triphosphate ( K i = 5.81 ± 1.54 μM). 4. 4. In equilibrium competition experiments, the adenosine analogs R-phenylisopropyladenosine, cyclohexyladenosine, N-ethylcarboxamidoadenosine, 2-chloroadenosine, S-phenylisopropyladenosine and the antagonists 8-cyclopentyl-1,3-dipropylxanthine and theophylline all displaced [ 3H]-cyclohexyladenosine from high-affinity binding sites with the rank order of potency in displacing characteristics of an A 1 adenosine receptor.