The modulatory effects of the anxiolytic etifoxine on GABA(A) receptors are mediated by the beta subunit.
The anxiolytic compound etifoxine (2-ethylamino-6-chloro-4-methyl-4-phenyl-4H-3,1-benzoxazine hydrochloride) potentiates GABA(A) receptor function in cultured neurons (Neuropharmacology 39 (2000) 1523). However, the molecular mechanisms underlying these effects are not known. In this study, we have determined the influence of GABA(A) receptor subunit composition on the effects of etifoxine, using recombinant murine GABA(A) receptors expressed in Xenopus oocytes. Basal chloride currents mediated by homomeric beta receptors were reduced by micromolar concentrations of etifoxine, showing that beta subunits possess a binding site for this modulator. In oocytes expressing alpha(1)beta(x) GABA(A) receptors (x=1, 2 or 3), etifoxine evoked a chloride current in the absence of GABA and enhanced GABA (EC10)-activated currents, in a dose-dependent manner. Potentiating effects were also observed with alpha(2)beta(x), beta(x)gamma(2s) or alpha(1)beta(x)gamma(2s) combinations. The extent of potentiation was clearly beta-subunit-dependent, being more pronounced at receptors containing a beta(2) or a beta(3) subunit than at receptors incorporating a beta(1) subunit. The mutation of Asn 289 in the channel domain of beta(2) to a serine (the homologous residue in beta(1)) did not significantly depress the effects of etifoxine at alpha(1)beta(2) receptors. This specific pattern of inhibition/potentiation was compared with that of other known modulators of GABA(A) receptor function like benzodiazepines, neurosteroids, barbiturates or loreclezole.
Hamon
Alain
A
Laboratoire de Neurophysiologie, UPRES EA 2647 (RCIM), Université d'Angers, UFR Sciences, 2 Boulevard Lavoisier, F-49045 01, Angers cedex, France. alain.hamon@univ-angers.fr
Morel
Alain
A
Hue
Bernard
B
Verleye
Marc
M
Gillardin
Jean Marie
JM
D000818:Animals; D014151:Anti-Anxiety Agents / Q000737:chemistry / Q000494:pharmacology*; D004305:Dose-Response Relationship, Drug; D005260:Female; D058785:GABA-A Receptor Agonists; D058787:GABA-A Receptor Antagonists; D009865:Oocytes / Q000187:drug effects / Q000502:physiology; D010078:Oxazines / Q000737:chemistry / Q000494:pharmacology*; D051381:Rats; D011963:Receptors, GABA-A / Q000502:physiology*; D014982:Xenopus laevis; D005680:gamma-Aminobutyric Acid / Q000494:pharmacology
D014151:Anti-Anxiety Agents; D058785:GABA-A Receptor Agonists; D058787:GABA-A Receptor Antagonists; D010078:Oxazines; D011963:Receptors, GABA-A; D005680:gamma-Aminobutyric Acid; C002125:etifoxine