Binding of the novel adenosine A(2A) receptor-selective antagonist radioligand [2-H-3]-4-(2-[7-amino-2-(2-furyl)(1,2,4)triazolo(2,3-a)(1,3,5,)triazin-5-yl amino]ethyl)phenol ([H-3]ZM241385) was examined using particulate preparations and frozen sections of rat brain. In membranes from the rat striatum, binding was saturable, reversible and temperature-dependent. Analysis of saturation isotherms indicated that [H-3]ZM241385 bound with high affinity (K-d of 0.84 nM). high density (1680 fmol mg protein(-1)) and with a high proportion of specific binding (93% at 1 nM radioligand). Examination of competition profiles indicated that [H-3]ZM241385 bound to sites with an A,, adenosine receptor-like rank order. The presence of guanosine 5'-(3-thio)-triphosphate failed to alter either [SH]ZM241385 binding or agonist competition for [H-3]ZM241385 binding. Autoradiographic analysis of [H-3]ZM241385 binding to frozen sections of rat brain indicated specific binding to the rat striatum of similar affinity (K-d of 0.43 nM) and susceptibility to adenosine receptor ligands. At 1 nM [H-3]ZM241385, specific binding comprised 95 +/- 1% total binding. In the hippocampus and frontal cortex, binding of [H-3]ZM241385 failed to saturate and was of lower density. Taken together, these results indicate that [H-3]ZM241385 should prove to be a useful radioligand in the characterisation of adenosine A(2A) receptors. (C) 2001 Elsevier Science B.V. All rights reserved.
