Identification and characterization of imidazoline-binding sites from calf striatum.

"Non-adrenoceptor'-binding sites for [3H]clonidine (I1-sites) and [3H]idazoxan (I2-sites) are identified in calf striatum membranes. The pharmacological profile of both subtypes was investigated by competition binding with the imidazolines idazoxan, cirazoline, Bu 224 (2-(4,5-dihydroimidaz-2-yl)-quinoline) and Bu 239 (2-(4,5-dihydroimidaz-2-yl)-quinoxaline); the guanidino derivatives clonidine, moxonidine, guanabenz, amiloride and agmatine; the oxazoline rilmenidine and the imidazole histamine. The competition experiments indicate that both populations of imidazoline-binding sites in calf striatum consist of a high- (H) and a low-affinity (L) compartment. The monoamine oxidase (MAO) inhibitors pargyline (non-selective) and deprenyl (MAO-B-selective) have micromolar affinity for the I1-sites and much lower affinity for the I2-sites. The venom of the marine snail Conus geographus is the most potent of the 13 tested Conus venom preparations. None of the tested venoms is able to discriminate between both sites.