title: Ascorbate/Fe(3+)-induced peroxidation and inhibition of the binding of A1 adenosine receptor ligands in rat brain membranes.
abstract: The effect of peroxidation induced by the ascorbate/Fe3+ system on the binding properties of the A1 adenosine receptor, was studied in rat brain membranes, using the agonist, [3H]R-N6-phenylisopropyladenosine ([3H]R-PIA), and the antagonist, [3H]1,3-dipropyl-8-cyclopentylxanthine ([3H]DPCPX). For the agonist, as well as for the antagonist, the number of binding sites (Bmax) was significantly (P < 0.05) reduced after pretreatment of the membranes with ascorbate/Fe3+. The affinity of the agonist for the binding sites was not statistically modified (P > 0.05) after ascorbate/Fe3+ pretreatment, whereas the Kd value of the antagonist was increased (P < 0.05) by a factor of 2. Ascorbate/Fe3+ pretreatment affected agonist binding in the presence of GTP in a similar way as that observed in the absence of GTP, suggesting that peroxidation also affects agonist binding to A1 adenosine receptors uncoupled to G-proteins. The results suggest that when brain membranes suffer free radical oxidative damage, the adenosine modulation of neuronal activity through A1 receptors could be less efficient.
authors.affiliation: Laboratory of Pharmacology, Gulbenkian Institute of Science, Oeiras, Portugal.
authors.forename: J C
authors.initials: JC
authors.lastname: Oliveira
authors.forename: M D
authors.initials: MD
authors.lastname: Constantino
authors.forename: A M
authors.initials: AM
authors.lastname: Sebastião
authors.forename: J A
authors.initials: JA
authors.lastname: Ribeiro
mesh_terms: D000818:Animals; D001205:Ascorbic Acid / Q000494:pharmacology*; D001665:Binding Sites / Q000187:drug effects; D001921:Brain / Q000378:metabolism*; D005290:Ferric Compounds / Q000494:pharmacology*; D006160:Guanosine Triphosphate / Q000494:pharmacology; D008024:Ligands; D008054:Lipid Peroxides / Q000378:metabolism*; D008297:Male; D008566:Membranes / Q000378:metabolism; D010660:Phenylisopropyladenosine / Q000378:metabolism; D058915:Purinergic P1 Receptor Antagonists; D051381:Rats; D017208:Rats, Wistar; D018047:Receptors, Purinergic P1 / Q000378:metabolism*; D014970:Xanthines / Q000378:metabolism
chemical_list: D005290:Ferric Compounds; D008024:Ligands; D008054:Lipid Peroxides; D058915:Purinergic P1 Receptor Antagonists; D018047:Receptors, Purinergic P1; D014970:Xanthines; D010660:Phenylisopropyladenosine; D006160:Guanosine Triphosphate; C051360:1,3-dipropyl-8-cyclopentylxanthine; D001205:Ascorbic Acid