TitleA subset of kappa opioid ligands bind to the membrane glucocorticoid receptor in an amphibian brain
Publication TypeJournal Article
Year of Publication2000
AuthorsEvans, SJ, Searcy, BT, Moore, FL
Type of ArticleJournal Article

Previous studies demonstrated that a membrane receptor for glucocorticoids (mGR) exists in neuronal membranes from the roughskin newt (Taricha granulosa) and that this receptor appears to be a G protein-coupled receptor (GPCR). The present study investigated the question of whether this mGR recognizes nonsteroid ligands that bind to cognate receptors in the GPCR superfamily. To address this question, ligand-binding competition studies evaluated the potencies of various ligands to displace [H-3]corticosterone (CORT) binding to neuronal membranes. Initial screening studies tested 21 different competitors and found that [H-3]CORT binding was displaced only by dynorphin 1-13 amide (an endogenous kappa-selective opioid peptide), U50,488 (a synthetic kappa-specific agonist) and naloxone (a nonselective opioid antagonist). Follow-up studies revealed that the kappa agonists bremazocine (BRE) and ethylketocyclazocine (EKC) also displaced [H-3]CORT binding to neuronal membranes, but that U69,593 (a kappa specific agonist) and nor-BNI (a kappa specific antagonist) were ineffective. The K-i values measured for the opioid competitors were in the subnanomolar to low micromolar range and had the following rank-order: dynorphin > U50,488 > naloxone > BRE > EKC. Because these ligands displaced, at most, only 70% of [H-3]CORT specific binding, it appears that some [H-3]CORT binding sites are opioid insensitive. Kinetic analysis of [H-3]CORT off-rates in the presence of U50,488 and/or CORT revealed no differences in dissociation rate constants, suggesting that there is a direct, rather than allosteric, interaction with the [H-3]CORT binding site. In summary, these results are consistent with the hypothesis that the high-affinity membrane binding site for [H-3] CORT is located on a kappa opioid-like receptor.

URL<Go to ISI>://WOS:000088386200003