title: Identification of A1 and A2 adenosine receptors in the rat spinal cord.
abstract: The adenosine receptors in membranes prepared from rat ventral and dorsal lumbar spinal cord were characterized by comparing the binding characteristics of [3H]5'-N-ethylcarboxamide adenosine ([3H]NECA), an agonist with nearly equal affinities at the A1 and A2 adenosine receptor subtypes, with those of [3H]N6-[(R)-1-methyl-2-phenylethyl]adenosine ([3H]R-PIA), an A1-selective agonist. Saturation isotherms of the ventral and dorsal spinal cord yielded Kd values 1.9 to 2.3 nM for [3H]R-PIA and 18.1 to 19.5 nM for [3H]NECA. The Bmax for [3H]NeCA was approximately twice the Bmax for [3H]R-PIA in ventral and dorsal halves (267 vs. 128 fmol/mg of protein and 402 vs. 206 fmol/mg of protein, respectively). Displacement of specific [3H]NECA binding by the A2-selective agonist, 2-(phenylamino)adenosine, the relatively nonselective antagonist, theophylline and six A1-selective agonists, R-PIA, S-PIA, N6-(cyclohexyl)adenosine, N6-(cyclopentyl)adenosine, N6-(m-aminophenyl)adenosine and N6-(m-iodophenyl)adenosine, revealed two [3H]NECA binding components with the characteristics of A1 and A2 receptors. All curves best fit a two-site model when analyzed by the computer program LIGAND. R-PIA, N6-(cyclohexyl)adenosine and N6-(cyclopentyl)adenosine were the most potent displacers at the first site (Ki = 0.6-1.4 nM). All A1-selective agonists were poor displacers of [3H]NECA at the second site (Ki = 0.6-18.6 microM). The A2-selective agonist, 2-(phenylamino)adenosine, was as potent as R-PIA in displacing [3H]NECA from this site with a Ki value 0.57 microM. Finally, the A1 and A2 adenosine receptor-mediated inhibition and stimulation of adenylate cyclase were demonstrated directly in synaptic membranes prepared from the spinal cord.
authors: Department of Pharmacology, University of Illinois, College of Medicine, Chicago.
authors: J I
authors: JI
authors: Choca
authors: H K
authors: HK
authors: Proudfit
authors: R D
authors: RD
authors: Green
mesh_terms: D000241:Adenosine / Q000031:analogs & derivatives / Q000378:metabolism / Q000494:pharmacology; D019830:Adenosine-5'-(N-ethylcarboxamide); D000262:Adenylyl Cyclases / Q000032:analysis; D000698:Analgesia; D000818:Animals; D004305:Dose-Response Relationship, Drug; D005033:Ethylmaleimide / Q000494:pharmacology; D005260:Female; D007700:Kinetics; D008297:Male; D051381:Rats; D011919:Rats, Inbred Strains; D011983:Receptors, Purinergic / Q000032:analysis*; D013116:Spinal Cord / Q000032:analysis*
chemical_list: D011983:Receptors, Purinergic; C047235:N-(1-methyl-2-phenylethyl)adenosine; D019830:Adenosine-5'-(N-ethylcarboxamide); C027513:N(6)-cyclohexyladenosine; C048599:N(6)-cyclopentyladenosine; D000262:Adenylyl Cyclases; D000241:Adenosine; D005033:Ethylmaleimide