title: Characterization of [3H]clonidine binding to two sites in calf brain membranes.
abstract: Kinetic studies showed that under appropriate conditions, [3H]clonidine binds to two distinct receptor sites in calf cortex membranes. At 23 degrees C, binding was obtained at a low-affinity site (dissociation constant, KD = 5.4 nM) and a high-affinity site (KD = 1.1 nM). In contrast, at 0 degree C, selective binding occurred to the low-affinity site only. Consequently, at 0 degree C, it was possible to evaluate the interaction of drugs with the low-affinity receptor directly. On the other hand, competition with the high-affinity receptor could be ascertained by generating displacement curves representing the differential between specific binding values obtained at 23 and 0 degree C. Guanine nucleotides selectively decreased binding to the high-affinity site without apparent influence on the low-affinity [3H]clonidine binding. The activities of various pharmacological agents at the low- and high-affinity clonidine receptors are discussed and compared with WB-4101 binding data.
mesh_terms: D000317:Adrenergic alpha-Antagonists / Q000378:metabolism; D000818:Animals; D001665:Binding Sites; D001667:Binding, Competitive; D001921:Brain / Q000378:metabolism*; D002417:Cattle; D002540:Cerebral Cortex / Q000378:metabolism*; D003000:Clonidine / Q000378:metabolism*; D004146:Dioxanes / Q000378:metabolism; D006160:Guanosine Triphosphate / Q000494:pharmacology; D007700:Kinetics; D011942:Receptors, Adrenergic, alpha / Q000378:metabolism
chemical_list: D000317:Adrenergic alpha-Antagonists; D004146:Dioxanes; D011942:Receptors, Adrenergic, alpha; D006160:Guanosine Triphosphate; C010654:(2-(2',6'-dimethoxy)phenoxyethylamino)methylbenzo-1,4-dioxane; D003000:Clonidine