Biochemical and pharmacological characterization of adenosine A1 receptors in eel (Anguilla anguilla) brain

Abstract

N 6 -cyclohexyl[3H]adenosine ([ 3 H]CHA) was used to label adenosine Al receptors in membranes prepared from male and female eel whole brain. The Al receptor agonist [ 3 H]CHA bound saturably, reversibly and with high affinity (Kd = 0.91 ± 0.12 nM; Bma = 120.36 5.2 fmol mg 1 protein). In equilibrium competition experiments, the adenosine agonists and antagonists all displaced [ 3 H]CHA from high-affinity binding sites with the rank order of potency in displacing, characteristics of an Al adenosine receptor. Mg 2 ' dramatically increased the affinity of [ 3 H]CHA without modifying the maximal binding capacity. The specific binding was inhibited by guanosine 5'-triphosphate (K i = 2.54 i 0.98 M). The [ 3 H]CHA binding sites are ubiquitously distributed with a maximum in cerebellum and a minimum in olfactory bulb. No difference was observed between male and female brain. In eel brain, synaptosomes (P2), stimulation of adenosine 3',5'-monophosphate (cyclic AMP) accumulation with 10 -5 M forskolin was markedly reduced (45.5%) by treatment with the adenosine Al receptor agonist CHA (10 -M), and the reduction was reversed in presence of the selective Al receptor antagonist 8-cyclopentyltheophylline (10-5 M). In superfused eel cerebellar synaptosomes, K + stimulated the release of adenosine in a partially Ca 2 +-dependent manner. The findings, taken together, suggest the hypothesis that adenosine Al receptors present in eel brain could modulate synaptic transmission, as Al receptors do in other vertebrates.

Evolutionary origins of the purinergic signalling system

“…1999). A 1 receptors have also been identified and pharmacologically characterized in the brain of the eel Anguilla anguilla (Poli et al. 1997).…”