title: Characterization of A2A adenosine receptors in human lymphocyte membranes by [3H]-SCH 58261 binding.
abstract: 1. The present study describes for the first time the characterization of the adenosine A2A receptor in human lymphocyte membranes with the new potent and selective antagonist radioligand, [3H]-5-amino-7-(2-phenylethyl)-2-(2-furyl)-pyrazolo [4,3-e]-1,2,4 triazolo [1,5-c] pyrimidine, ([3H]-SCH 58261). In addition, both receptor affinity and potency of reference adenosine receptor agonists and antagonists were determined in binding and adenylyl cyclase studies. 2. Saturation experiments revealed a single class of binding sites with Kd and Bmax values of 0.85 nM and 35 fmol mg-1 protein, respectively. A series of adenosine receptor ligands were found to compete for the binding of 0.8 nM [3H]-SCH 58261 to human lymphocyte membranes with a rank order of potency consistent with that typically found for interactions with the A2A-adenosine receptor. In the adenylyl cyclase assay the same compounds exhibited a rank order of potency similar to that observed in binding experiments. 3. Thermodynamic data indicate that [3H]-SCH 58261 binding to human lymphocytes is entropy and enthalpy-driven, a finding in agreement with the thermodynamic behaviour of antagonists for rat striatal A2A-adenosine receptors. 4. It is concluded that in human lymphocyte membranes [3H]-SCH 58261 directly labels binding sites showing the characteristic properties of the adenosine A2A-receptor. The presence of A2A-receptors in peripheral tissue such as human lymphocytes strongly suggests an important role for adenosine in modulating immune and inflammatory responses.
authors.affiliation: Department of Clinical and Experimental Medicine, University of Ferrara, Italy.
authors.forename: K
authors.initials: K
authors.lastname: Varani
authors.forename: S
authors.initials: S
authors.lastname: Gessi
authors.forename: A
authors.initials: A
authors.lastname: Dalpiaz
authors.forename: E
authors.initials: E
authors.lastname: Ongini
authors.forename: P A
authors.initials: PA
authors.lastname: Borea
mesh_terms: D002462:Cell Membrane / Q000187:drug effects; D000242:Cyclic AMP / Q000096:biosynthesis; D006801:Humans; D008214:Lymphocytes / Q000187:drug effects / Q000378:metabolism*; D058906:Purinergic P1 Receptor Agonists; D011743:Pyrimidines / Q000737:chemistry / Q000378:metabolism* / Q000494:pharmacology; D043705:Receptor, Adenosine A2A; D018047:Receptors, Purinergic P1 / Q000097:blood; D013816:Thermodynamics; D014230:Triazoles / Q000737:chemistry / Q000378:metabolism* / Q000494:pharmacology; D014316:Tritium
chemical_list: C098657:5-amino-7-(2-phenylethyl)-2-(2-furyl)pyrazolo(4,3-e)-1,2,4-triazolo(1,5-c)pyrimidine; D058906:Purinergic P1 Receptor Agonists; D011743:Pyrimidines; D043705:Receptor, Adenosine A2A; D018047:Receptors, Purinergic P1; D014230:Triazoles; D014316:Tritium; D000242:Cyclic AMP