We have used the antagonist radioligand 8-cyclopentyl-1,3-[3H]dipropylxanthine to label adenosine recognition sites in porcine atrial membranes. 8-Cyclopentyl-1,3-[3H]dipropylxanthine bound saturably, reversibly and with high affinity to an apparently homogenous population of recognition sites with a Bmax of 32.0 ± 0.9 fmol/mg protein and a KD of 0.394 ± 0.049 nM. Prototypic adenosine receptor agonists inhibited the specific binding of 8-cyclopentyl-1,3-[3H]dipropylxanthi in a manner consistent with the labeling of an A1 adenosine receptor. 8-Cyclopentyl-1,3-[3H]dipropylxanthine appears to be a valuable antagonist radioligand for the characterization of cardiac adenosine receptors.
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