title: Binding of the A1-selective adenosine antagonist 8-cyclopentyl-1,3-dipropylxanthine to rat brain membranes.
abstract: 8-Cyclopentyl-1,3-dipropylxanthine (PD 116,948) is a very potent, very A1-selective adenosine antagonist, with a Ki of 0.46 nM in 3H-CHA binding to A1 receptors in rat whole brain membranes and 340 nM in 3H-NECA binding to A2 receptors in rat striatal membranes. Its 740-fold A1-selectivity is the highest reported for an adenosine antagonist. 3H-PD 116,948 (117 Ci/mmol) was prepared by reduction of the diallyl analog. 3H-PD 116,948 bound to a single site in rat whole brain membranes, with a Bmax of 46 pmol/g wet weight and Kd of 0.42 nM. Nonspecific binding was extremely low, amounting to about 3% of total binding under standard conditions and less than 1% when higher tissue concentrations were used. Affinities of compounds for inhibition of 3H-PD 116,948 binding were highly consistent with an A1 adenosine receptor. Antagonists were equally potent in 3H-PD 116,948 binding and in 3H-CHA binding, while agonists were consistently about 12-fold more potent in 3H-CHA binding. Hill coefficients were 1.0 for antagonists and about 0.65 for agonists. 3H-PD 116,948 should be a useful antagonist ligand for adenosine A1 receptors.
mesh_terms: D000241:Adenosine / Q000031:analogs & derivatives / Q000037:antagonists & inhibitors* / Q000494:pharmacology; D000818:Animals; D001921:Brain / Q000378:metabolism*; D002462:Cell Membrane / Q000378:metabolism; D005260:Female; D007700:Kinetics; D009705:Nucleosides / Q000378:metabolism; D051381:Rats; D014970:Xanthines / Q000138:chemical synthesis / Q000378:metabolism* / Q000494:pharmacology
chemical_list: D009705:Nucleosides; D014970:Xanthines; C048599:N(6)-cyclopentyladenosine; C051360:1,3-dipropyl-8-cyclopentylxanthine; D000241:Adenosine