Binding of [3H]cyclohexyladenosine to adenosine recognition sites in guinea pig ileal membranes: comparison with binding in brain membranes.

The stable adenosine agonist [3H]cyclohexyladenosine binds to membranes prepared from guinea pig myenteric plexus with high affinity (Kd = 1.8 nM) in a saturable, reversible manner. Binding pharmacology was consistent with the labelling of an A1 type adenosine receptor with the R-isomer of N6-phenylisopropyladenosine (PIA) being 11 times more potent than the S-diastereomer. Binding was similar to that observed in brain tissue being displaced by a number of xanthine adenosine antagonists. In terms of density of binding sites, however, there were approximately 9 times fewer higher affinity binding sites in ileal membranes than in the central nervous system.