title: Characterization and localization of [3H]-clonidine binding in membranes prepared from guinea-pig spleen.
abstract: 1. [3H]-Clonidine binds to membranes prepared from guinea-pig spleen with high affinity. 2. Kinetic experiments indicated that [3H]-clonidine associates rapidly to the binding site and that the binding is reversible. A study of the dissociation of [3H]-clonidine from splenic membranes revealed two components. The slowly dissociating component corresponded to a high affinity process (Kd = 2.1 nmol/l) in good agreement to that obtained by saturation analysis. 3. Over the concentration range used, saturation experiments revealed only a single population of sites with a dissociation constant (Kd) of 2.4 nmol/l and a density of 5.1 pmol/g wet weight tissue. 4. Examination of the relatively potency of a series of alpha-adrenoceptor agonists and antagonists indicates that [3H]-clonidine binding is to alpha 2-adrenoceptors. 5. High levels of binding were obtained to lymphocytes prepared from guinea-pig spleen and to membranes from the splenic capsule. Pretreatment of animals with 6-hydroxydopamine produced changes in apparent affinity of binding with little change in the number of receptor sites. 6. It is concluded that [3H]-clonidine labels is a site resembling the alpha 2-adrenoceptor in guinea-pig spleen. Few if any of these sites are located prejunctionally and a significant fraction are associated with lymphocytes.
mesh_terms: D000818:Animals; D001667:Binding, Competitive; D003000:Clonidine / Q000378:metabolism*; D006168:Guinea Pigs; D006892:Hydroxydopamines / Q000494:pharmacology; D066298:In Vitro Techniques; D007668:Kidney / Q000378:metabolism; D007700:Kinetics; D008214:Lymphocytes / Q000378:metabolism; D008297:Male; D008566:Membranes / Q000378:metabolism; D011485:Protein Binding; D011942:Receptors, Adrenergic, alpha / Q000378:metabolism; D013154:Spleen / Q000378:metabolism*
chemical_list: D006892:Hydroxydopamines; D011942:Receptors, Adrenergic, alpha; D003000:Clonidine