title: Solubilized rat brain adenosine receptors have two high-affinity binding sites for 1,3-dipropyl-8-cyclopentylxanthine.
abstract: The specific binding of L-N6-[3H]phenylisopropyladenosine (L-[3H]PIA) to solubilized receptors from rat brain membranes was studied. The interaction of these receptors with relatively low concentrations of L-[3H]PIA (0.5-12.0 nM) in the presence of Mg2+ showed the existence of two binding sites for this agonist, with respective dissociation constant (KD) values of 0.24 and 3.56 nM and respective receptor number (Bmax) values of 0.28 +/- 0.03 and 0.66 +/- 0.05 pmol/mg of protein. In the presence of GTP, the binding of L-[3H]PIA also showed two sites with KD values of 24.7 and 811.5 nM and Bmax values of 0.27 +/- 0.09 and 0.93 +/- 0.28 pmol/mg of protein for the first and the second binding site, respectively. Inhibition of specific L-[3H]PIA binding by 1,3-dipropyl-8-cyclopentylxanthine (DPCPX) (0.1-300 nM) performed with the same preparations revealed two DPCPX binding sites with Ki values of 0.29 and 13.5 nM, respectively. [3H]DPCPX saturation binding experiments also showed two binding sites with respective KD values of 0.81 and 10.7 nM and respective Bmax values of 0.19 +/- 0.02 and 0.74 +/- 0.06 pmol/mg of protein. The results suggest that solubilized membranes from rat brain possess two adenosine receptor subtypes: one of high affinity with characteristics of the A1 subtype and another with lower affinity with characteristics of the A3 subtype of adenosine receptor.
authors.affiliation: Laboratory of Pharmacology, Gulbenkian Institute of Science, Oeiras, Portugal.
authors.forename: J C
authors.initials: JC
authors.lastname: Oliveira
authors.forename: A M
authors.initials: AM
authors.lastname: Sebastião
authors.forename: J A
authors.initials: JA
authors.lastname: Ribeiro
mesh_terms: D000818:Animals; D001665:Binding Sites; D001667:Binding, Competitive; D001921:Brain / Q000378:metabolism*; D006160:Guanosine Triphosphate / Q000494:pharmacology; D015636:Magnesium Chloride / Q000494:pharmacology; D008297:Male; D010660:Phenylisopropyladenosine / Q000378:metabolism; D051381:Rats; D011919:Rats, Inbred Strains; D011983:Receptors, Purinergic / Q000378:metabolism*; D012995:Solubility; D014970:Xanthines / Q000378:metabolism* / Q000494:pharmacology
chemical_list: D011983:Receptors, Purinergic; D014970:Xanthines; D015636:Magnesium Chloride; D010660:Phenylisopropyladenosine; D006160:Guanosine Triphosphate; C051869:8-(4-((2-aminoethyl)aminocarbonylmethyloxy)phenyl)-1,3-dipropylxanthine; C051360:1,3-dipropyl-8-cyclopentylxanthine