Methadone: Does it really have low efficacy at mu-opioid receptors?

I Rodriguez-Martin, E Braksator, C P Bailey, S Goodchild, N V Marrion, E Kelly, G Henderson

Research output: Contribution to journalArticlepeer-review

17 Citations (SciVal)


There is confusion in the literature concerning the relative agonist efficacy of methadone at mu-opioid receptors (MOPrs). Here, we confirm that methadone is a full agonist in guanosine 5'-O-[gamma-thio]triphosphate (GTP gamma S) binding studies. Methadone, however, seems to have low efficacy in studies of MOPr activation of G-protein-gated potassium (GIRK) channels, but this is because it directly inhibits the GIRK channels. Methadone also inhibits alpha(2)-adrenoceptor-activated GIRK channels. Methadone is not a specific GIRK channel blocker. It also inhibits small conductance Ca2+-activated K+ (SK2) channels. We conclude that methadone is a full agonist at MOPrs that, as we and others have shown, induces MOPr desensitization and internalization.
Original languageEnglish
Pages (from-to)589-593
Number of pages5
Issue number5
Publication statusPublished - Mar 2008

Bibliographical note

ID number: ISI:000254372100016


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