Molecular Probes for Adenosine Receptors
High affinity adenosine agonists and antagonists have been developed as radioligands for characterizing adenosine receptors in binding studies. Previous studies have utilized reversibly binding tritiated ligands such as the A1-selective agonists (Table 1) N6-cyclohexyladenosine, 1 (Bruns et al, 1983), and R-N6-(phenylisopropyl)adenosine, 2 (Schwabe and Trost, 1980), or the A1-selective antagonists (Table 2), XAC, 7 (xanthine amine congener, 8-((2-aminoethyl)-aminocarbonylmethyloxyphenyl)-l,3-dipropybcanthine) (Jacobson et al, 1986) and CPX, 6 (l,3-dipropyl-8-cyclopentylxanthine) (Bruns et al, 1987). [3H]CPX has a Kd at rat brain A1 receptors of 0.42 nM and a Ki at A2 receptors of 410 nM. At present, [3H]CPX is the most A1-selective among the commonly used antagonist radioligands. pH]XAC is 60-fold A1-selective in the rat brain and is of nearly the same affinity (Kd = 1.2 nM) as CPX.
KeywordsAdenosine Caffeine Theophylline Biotin Purine
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