Salvinorin A: Allosteric interactions at the μ-opioid receptor

Richard B. Rothman, Daniel L. Murphy, Heng Xu, Jonathan A. Godin, Christina M. Dersch, John S. Partilla, Kevin Tidgewell, Matthew Schmidt, Thomas E. Prisinzano

Research output: Contribution to journalArticlepeer-review

59 Scopus citations

Abstract

Salvinorin A [(2S,4aR,6aR,7R,9S,10aS,10bR)-9-(acetyloxy)-2-(3-furanyl)- dodecahydro-6a,10b-dimethyl-4,10-dioxo-2h-naphtho[ 2,1-c]pyran-7-carboxylic acid methyl ester] is a hallucinogenic κ-opioid receptor agonist that lacks the usual basic nitrogen atom present in other known opioid ligands. Our first published studies indicated that Salvinorin A weakly inhibited μ-receptor binding, and subsequent experiments revealed that Salvinorin A partially inhibited μ-receptor binding. Therefore, we hypothesized that Salvinorin A allosterically modulates μ-receptor binding. To test this hypothesis, we used Chinese hamster ovary cells expressing the cloned human opioid receptor. Salvinorin A partially inhibited [3H]Tyr-D-Ala-Gly-N-Me-Phe-Gly-ol (DAMGO) (0.5, 2.0, and 8.0 nM) binding with EMAX values of 78.6, 72.1, and 45.7%, respectively, and EC50 values of 955, 1124, and 4527 nM, respectively. Salvinorin A also partially inhibited [3H] diprenorphine (0.02, 0.1, and 0.5 nM) binding with EMAX values of 86.2, 64, and 33.6%, respectively, and EC50 values of 1231, 866, and 3078 nM, respectively. Saturation binding studies with [3H]DAMGO showed that Salvinorin A (10 and 30 μM) decreased the μ-receptor B max and increased the Kd in a dose-dependent nonlinear manner. Saturation binding studies with [3H]diprenorphine showed that Salvinorin A (10 and 40 μM) decreased the μ-receptor Bmax and increased the Kd in a dose-dependent nonlinear manner. Similar findings were observed in rat brain with [3H]DAMGO. Kinetic experiments demonstrated that Salvinorin A altered the dissociation kinetics of both [3H]DAMGO and [3H]diprenorphine binding to μ receptors. Furthermore, Salvinorin A acted as an uncompetitive inhibitor of DAMGO-stimulated guanosine 5′-O-(3-[35S]thio)-triphosphate binding. Viewed collectively, these data support the hypothesis that Salvinorin A allosterically modulates the μ-opioid receptor.

Original languageEnglish
Pages (from-to)801-810
Number of pages10
JournalJournal of Pharmacology and Experimental Therapeutics
Volume320
Issue number2
DOIs
StatePublished - Feb 2007

ASJC Scopus subject areas

  • Molecular Medicine
  • Pharmacology

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