title: Agonist-induced desensitization and down-regulation of the human kappa opioid receptor expressed in Chinese hamster ovary cells.
abstract: In this study, we examined whether the human kappa opioid receptor stably expressed in Chinese hamster ovary cells underwent desensitization and down-regulation after prolonged exposure to the agonist (-)U50,488H. Pretreatment with (-)U50,488H led to a reduction in the magnitude of increase in [35S]GTPgammaS binding by the subsequent application of (-)U50,488H. The extent of desensitization was related to duration of exposure and (-)U50,488H concentration. Pretreatment with (-)U50,488H also reduced the potency of (-)U50,488H in inhibiting forskolin-stimulated adenylate cyclase. In membranes of (-)U50,488H-pretreated cells, the affinity of (-)U50,488H was lower than that in the untreated control, and GTPgammaS had no effect on (-)U50,488H affinity, consistent with the notion of uncoupling of the receptor-G protein complex by (-)U50, 488H treatment. Down-regulation of the kappa opioid receptor also occurred on exposure to (-)U50,488H. Higher (-)U50,488H concentrations and/or longer incubation periods were required for down-regulation than for desensitization. The degree of down-regulation depended on the agonist concentration and incubation time. (-)U50,488H-induced desensitization and down-regulation were blocked by naloxone. (+)U50,488H, an inactive stereoisomer, did not cause desensitization or down-regulation. These results indicate that both processes were receptor-mediated. After incubation with (-)U50,488H and removal of (-)U50,488H, both (-)U50,488H-induced [35S]GTPgammaS binding and receptor number returned to the control level, which indicates that both processes were reversible. Thus, desensitization and down-regulation of the kappa opioid receptor occur after agonist exposure and represent two different adaptation mechanisms.
authors.affiliation: Department of Pharmacology, Temple University School of Medicine, Philadelphia, Pennsylvania 19140, USA.
authors.forename: J
authors.initials: J
authors.lastname: Zhu
authors.forename: L Y
authors.initials: LY
authors.lastname: Luo
authors.forename: G F
authors.initials: GF
authors.lastname: Mao
authors.forename: B
authors.initials: B
authors.lastname: Ashby
authors.forename: L Y
authors.initials: LY
authors.lastname: Liu-Chen
mesh_terms: D019900:3,4-Dichloro-N-methyl-N-(2-(1-pyrrolidinyl)-cyclohexyl)-benzeneacetamide, (trans)-Isomer / Q000494:pharmacology*; D000262:Adenylyl Cyclases / Q000187:drug effects / Q000378:metabolism; D000818:Animals; D000959:Antihypertensive Agents / Q000494:pharmacology*; D001667:Binding, Competitive; D016466:CHO Cells / Q000187:drug effects; D005576:Colforsin / Q000494:pharmacology; D006224:Cricetinae; D015536:Down-Regulation; D004789:Enzyme Activation; D016244:Guanosine 5'-O-(3-Thiotriphosphate) / Q000378:metabolism; D006801:Humans; D017473:Receptors, Opioid, kappa / Q000187:drug effects* / Q000378:metabolism
chemical_list: D000959:Antihypertensive Agents; D017473:Receptors, Opioid, kappa; D005576:Colforsin; D016244:Guanosine 5'-O-(3-Thiotriphosphate); D019900:3,4-Dichloro-N-methyl-N-(2-(1-pyrrolidinyl)-cyclohexyl)-benzeneacetamide, (trans)-Isomer; D000262:Adenylyl Cyclases