RT Journal Article
SR Electronic
T1 Agonist-Induced Desensitization and Down-regulation of the Human<em>Kappa</em> Opioid Receptor Expressed in Chinese Hamster Ovary Cells
JF Journal of Pharmacology and Experimental Therapeutics
JO J Pharmacol Exp Ther
FD American Society for Pharmacology and Experimental Therapeutics
SP 28
OP 36
VO 285
IS 1
A1 Zhu, Jinmin
A1 Luo, Lai-Yi
A1 Mao, Guan-Fen
A1 Ashby, Barrie
A1 Liu-Chen, Lee-Yuan
YR 1998
UL http://jpet.aspetjournals.org/content/285/1/28.abstract
AB In this study, we examined whether the human kappaopioid 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]GTPγS 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 GTPγS 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]GTPγS binding and receptor number returned to the control level, which indicates that both processes were reversible. Thus, desensitization and down-regulation of the kappaopioid receptor occur after agonist exposure and represent two different adaptation mechanisms. The American Society for Pharmacology and Experimental Therapeutics