Differentiating Adenosine Receptors and Adenosine Uptake Sites in Brain

Abstract

The characteristics of adenosine receptors and adenosine uptake sites in brain are presented. High affinity adenosine receptors of the A₁ type bind ³H]cyclohexyladenosine (³H]CHA) and ³ H]diethyl-phenyl-xanthine (³H]DPX) with 10^?9 potency while adenosine uptake sites are labeled 10^?10 potency with ³ H]nitrobenzyl-thioinosine (³H]NBI). NBI does not inhibit either ³H]CHA (agonist) or ³H]DPX (antagonist) binding to adenosine receptors in brain cortical membranes and conversely CHA and other adenosine receptor ligands are very poor inhibitors of ³H]NBI binding to adenosine uptake sites. A number of other differences between the receptor and uptake site are discussed which provide rather strong evidence that these two sites are quite distinct and that the labeled ligands used represent specific probes for each site.