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Differential Agonist Regulation of the Human κ‐Opioid Receptor
Author(s) -
Blake Allan D.,
Bot George,
Li Shuixing,
Freeman John C.,
Reisine Terry
Publication year - 1997
Publication title -
journal of neurochemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.75
H-Index - 229
eISSN - 1471-4159
pISSN - 0022-3042
DOI - 10.1046/j.1471-4159.1997.68051846.x
Subject(s) - levorphanol , agonist , pertussis toxin , adenylyl cyclase , diprenorphine , chemistry , etorphine , dynorphin , opioid receptor , receptor , hek 293 cells , pharmacology , opioid , endocrinology , dynorphin a , medicine , g protein , (+) naloxone , biochemistry , opioid peptide , biology
Opiates are potent analgesics used clinically in the treatment of pain. A significant drawback to the chronic use and clinical effectiveness of opiates is the development of tolerance. To investigate the cellular mechanisms of tolerance, the cloned human κ‐opioid receptor was stably expressed in human embryonic kidney (HEK 293) cells, and the effects of opioid agonist treatment were examined. The receptor‐expressing cells showed specific high‐affinity membrane binding for a κ‐selective opioid, 3 H‐labeled (+)‐(5α,7α,8β)‐ N ‐methyl‐ N ‐[7‐(1‐pyrrolidinyl)‐1‐oxaspiro[4,5]dec‐8‐yl]benzeneacetamide ([ 3 H]U69,593), and a nonselective opioid antagonist, [ 3 H]diprenorphine. Pretreatment with pertussis toxin or guanosine 5′‐ O ‐(3‐thiotriphosphate) reduced [ 3 H]69,593 binding, indicating that the human κ receptor coupled to G proteins of the G i or G o families in HEK 293 cells. The receptor‐mediated inhibition of adenylyl cyclase was abolished by pertussis toxin pretreatment and was blocked by a κ‐selective antagonist, norbinal‐torphimine. A 3‐h pretreatment with a κ‐selective agonist, (±)‐ trans ‐3,4‐dichloro‐ N ‐methyl‐ N ‐[2‐(1‐pyrrolidinyl)cyclohexyl]benzeneacetamide (U50,488), caused receptor down‐regulation, whereas no receptor down‐regulation was found after levorphanol pretreatment. U50,488 or dynorphin A 1–17 pretreatments (3 h) desensitized the ability of U50,488 or dynorphin A 1–17 to inhibit cyclic AMP accumulation, as evidenced by a decrease in functional potency. Also, U50,488 pretreatment desensitized the ability of levorphanol to inhibit forskolin‐stimulated cyclic AMP accumulation. In contrast, pretreatment of cells with either levorphanol or a potent nonselective opioid, etorphine, resulted in no apparent receptor desensitization. Taken together, these results demonstrate that the human κ receptor is differentially regulated by selective and nonselective opioid agonists, with selective agonists able to desensitize the receptor.