The in vitro and in vivo enantioselectivity of etomidate implicates the GABAA receptor in general anaesthesia

Delia Belelli, Anna-Lisa Muntoni, Simon D. Merrywest, Luc J. Gentet, Anna Casula, Helen Callachan, Paola Madau, David K. Gemmell, Niall M. Hamilton, Jeremy J. Lambert, Keith T. Sillar, John A. Peters

    Research output: Contribution to journalArticlepeer-review

    63 Citations (Scopus)

    Abstract

    General anaesthetics exhibiting enantioselectivity afford valuable tools to assess the fundamental mechanisms underlying anaesthesia. Here, we characterised the actions of the R-(+)- and S-(-)-enantiomers of etomidate. In mice and tadpoles, R-(+)-etomidate was more potent (˜10-fold) than S-(-)-etomidate in producing loss of the righting reflex. In electrophysiological and radioligand binding assays, the enantiomers of etomidate positively regulated GABAA receptor function at anaesthetic concentrations and with an enantioselectivity paralleling their in vivo activity. GABA-evoked currents mediated by human recombinant GABAA receptors were potentiated by either R-(+)- or S-(-)-etomidate in a manner dependent upon receptor subunit composition. A direct, GABA-mimetic, effect was similarly subunit dependent. Modulation of GABA receptor activity was selective; R-(+)-etomidate inhibited nicotinic acetylcholine, or 5-hydroxytryptamine3 receptor subtypes only at supra-clinical concentrations and ionotropic glutamate receptor isoforms were essentially unaffected. Acting upon reticulothalamic neurones in rat brain slices, R-(+)-etomidate prolonged the duration of miniature IPSCs and modestly enhanced their peak amplitude. S-(-)-etomidate exerted qualitatively similar, but weaker, actions. In a model of locomotor activity, fictive swimming in Xenopus laevis tadpoles, R-(+)- but not S-(-)-etomidate exerted a depressant influence via enhancement of GABAergic neurotransmission. Collectively, these observations strongly implicate the GABAA receptor as a molecular target relevant to the anaesthetic action of etomidate.
    Original languageEnglish
    Pages (from-to)57-71
    Number of pages15
    JournalNeuropharmacology
    Volume45
    Issue number1
    DOIs
    Publication statusPublished - Jul 2003

    Keywords

    • General anaesthesia
    • GABAA receptor
    • Etomidate
    • GABAergic inhibitory synaptic transmission

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