Fig 1.
Chemical structures of clobazam, N-desmethylclobazam and clonazepam.
Fig 2.
Functional properties of GABA at six human GABAARs expressed in Xenopus oocytes.
Concentration-response curves of GABA at the α1β2γ2S (circle), α2β2γ2S (square), α3β2γ2S (triangle), α5β2γ2S (inverted triangle), α6β2δ (diamond) and α6β2 (asterisk) GABAARs (means ± S.E.M.; N = 4–7).
Table 1.
Functional properties of GABA at the human α1β2γ2S, α2β2γ2S, α3β2γ2S, α5β2γ2S, α6β2δ and α6β2GABAARs expressed in Xenopus oocytes.
The EC50 values are given in μM with pEC50 ± S.E.M. values in brackets, and the Hill slopes (nH ± S.E.M.) and the numbers of experiments (N) are also given.
Fig 3.
Functional properties of clobazam, N-desmethylclobazam and clonazepam at four human GABAARs expressed in Xenopus oocytes.
(A) Representative traces for various concentrations of clobazam (top), N-desmethylclobazam (middle) and clonazepam (bottom) co-applied with GABA EC20 to oocytes expressing the α5β2γ2S GABAAR. The black bars represent applications of GABA EC20 and of 3 mM GABA that elicits maximal current through the receptor. The grey bars represent applications of various concentrations of clobazam, N-desmethylclobazam or clonazepam (a 30 s pre-incubation with the compound followed by co-application of the compound and GABA EC20). (B) Concentration-response relationships for clobazam (top), N-desmethylclobazam (middle) and clonazepam (bottom) at α1β2γ2S, α2β2γ2S, α3β2γ2S and α5β2γ2S GABAARs in the presence of GABA EC20 (means ± S.E.M.; N = 2–6).
Table 2.
Functional properties of clobazam, N-desmethylclobazam, and clonazepam at the human α1β2γ2S, α2β2γ2S, α3β2γ2S, α5β2γ2S, α6β2δ and α6β2GABAARs expressed in Xenopus oocytes.
Table 3.
Statistical analysis of the functional properties of clobazam, N-desmethylclobazam, and clonazepam at the human α1β2γ2S, α2β2γ2S, α3β2γ2S and α5β2γ2S GABAARs.
Fig 4.
Comparison of the functional efficacies of clobazam, N-desmethylclobazam, and clonazepam at α1,2,3,5β2γ2S GABAARs with those of diazepam and zolpidem.
(A) Potentiation of the response elicited by GABA EC20 by 3 μM diazepam in Xenopus oocytes injected with cRNAs encoding for α1β2γ2S, α2β2γ2S, α3β2γ2S and α5β2γ2S GABAARs in a subunit ratio of 1:1:1 (means ± S.E.M.; N = 2–4) (B) Potentiation of the response elicited by EC20 GABA by 3 μM clobazam and 3 μM zolpidem in Xenopus oocytes injected with cRNAs encoding the α2β2γ2S GABAAR injected in a subunit ratio of 1:1:5 (means ± S.E.M.; N = 2).
Fig 5.
Zinc-mediated inhibition of human α1β2 and α1β2γ2S GABAAR signalling in Xenopus oocytes.
(A) Representative trace of the inhibition mediated 100 μM Zn2+ of the currents elicited by 10 μM GABA (EC80) through the α1β2 GABAAR. (B) Representative trace of the inhibition mediated 100 μM Zn2+ of the currents induced by 100 μM GABA (EC80) through the α1β2γ2S GABAAR. (C) The degree of inhibition mediated by 100 μM Zn2+ of GABA EC80-evoked currents in oocytes expressing α1β2 mean ± S.E.M.; 77 ± 6.3%; N = 7and α1β2γ2S (mean ± S.E.M.; 4.7 ± 4.6%; N = 6) GABAARs.
Fig 6.
. Functional properties of clobazam, N-desmethylclobazam and clonazepam at the human α6β2δ and α6β2 GABAARs expressed in Xenopus oocytes.
(A) Representative traces for various concentrations of clobazam (top), N-desmethylclobazam (middle) and clonazepam (bottom) co-applied with GABA EC20 to oocytes expressing the α6β2δ GABAAR. The black bars represent applications of GABA EC20 and of 300 M GABA that elicits maximal current through the receptor. The grey bars represent applications of various concentrations of clobazam, N-desmethylclobazam or clonazepam (a 30 s pre-incubation with the compound followed by co-application of the compound and GABA EC20). (B) Concentration-response relationships for clobazam (top), N-desmethylclobazam (middle) and clonazepam (bottom) at the α6β2δ GABAAR and for N-desmethylclobazam at the α6β2 GABAAR (middle) in the presence of GABA EC20 (means ± S.E.M.; N = 4–6).