Autoradiographic evidence for G-protein coupled A2-receptors in rat neostriatum using [3H]-CGS 21680 as a ligand

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Abstract
Summary Recently [3H]-CGS 21680 (2-[p-(2-carbonylethyl)-phenylethylamino]-5′-N-ethylcarboxamidoadeno-sine) has been identified as a selective adenosine A2-receptor agonist. In this study the binding of [3H]-CGS 21680 to 10 μm sections of rat neostriatum was investigated with quantitative autoradiography. Specific, saturable binding was detectable, and Scatchard analysis of saturation experiments gave estimates for K D and B max of 1.7 nM and 322 fmol/mg protein, respectively. The rank order of potency for inhibition of [3H]-CGS 21680 binding was 5′-N-ethylcarboxamidoadenosine (1.9 nM) > 2-chloroadenosine (18 nM) > R-N6-phenylisoprop-yladenosine (59 nM) > S-N6-phenylisoprophyladeno sine (460 nM) > 1,3-dipropyl-8-cyclopentylxanthine (700 nM). The binding of [3H]-CGS 21680 was sensitive to GTP, since 1 μM GTP reduced binding to 4.7% of control. These data support the identity of CGS 21680 as an agonist at high affinity adenosine A2-receptors and indicate these receptors in rat striatum are coupled to guanine nucleotide binding proteins.

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