CHARACTERIZATION OF IMIDAZOLINE BINDING PROTEIN(S) SOLUBILIZED FROM HUMAN BRAIN-STEM - STUDIES WITH [H-3] IDAZOXAN AND [H-3] CLONIDINE

Imidazoline binding sites from the human brainstem were solubilized with 3-[(3-cholamidopropyl)-dimethylammonio]-1 -propane-sulfonate (CHAPS). [H-3]idazoxan and [H-3]clonidine were used as ligands to characterize the solubilized binding sites. In both the soluble and membrane fractions, [H-3]idazoxan binding was saturable, stereoselective, sensitive to imidazolines and insensitive to (-)norepinephrine and to amiloride. The affinities of [3H]idazoxan for the soluble and membrane sites were similar (K-D = 25+/-11 nM and 20+/-3 nM). In both soluble and membrane fractions, the alpha(2)-adrenoceptor binding bring masked with (-)norepinephrine, [H-3]clonidine bound to a low affinity site which was insensitive to (-)norepinephrine and which exhibited the same selectivity for various drugs as the [H-3]idazoxan binding site. alpha(2)-adrenoceptor binding was present in the membrane and the soluble fractions although if was difficult to detect in the soluble fraction because of inhibition of [H-3]rauwolscine binding by the CHAPS detergent.