Figure 3.

Stereoselective action of R-(−)-14 and S-(+)-14. (A) Two electrode voltage clamp was used to measure currents from oocytes injected with human α1β2γ2L GABA_A receptor subunits. Currents were elicited with 10 μM GABA (black bar) and twice the anesthetic dose of each compound sequentially applied to the same oocyte: 80 μM S-(+)-14 or 8 μM R-(−)-14 (grey bars). (B) 10 μM GABA currents were potentiated with increasing amounts of R-(−)-14 or S-(+)-14. Solid lines represent the non-linear least squares fit to the data. For R-(−)-14 (circles): EC₅₀ = 2.1 ± 1.2 μM, n_H = 1.4 ± 0.5, I_max = 23 ± 5 (data from 2 oocytes). 10 μM GABA current traces from a typical oocyte are shown in top inset with increasing amounts of R-(−)-14. S-(+)-14 (squares) was tested up to 300 μM (squares) and data could not be similarly fit. Traces from a typical oocyte in lower inset represent 10 μM GABA plus increasing amounts of S-(+)-14. (C) GABA concentration response curves shift to the left in the presence of R-(−)-14. Data is shown from one representative oocyte. Solid lines represent the non-linear least squares fit to the data: for GABA: EC₅₀ = 46 ± 1 μM, n_H = 1.8 ± 0.1, I_max = 0.9 ± 0.01 (open circles). In the presence of 8 μM R-(−)-14: EC₅₀ = 3.1 ± 0.1 μM, n_H = 1.0 ± 0.1, I_max = 1.2 ± 0.01 (closed circles). Currents were normalized to the maximal GABA response. Current traces in upper inset show the effect of 8 μM R-(−)-14 on 3 mM GABA current responses. Traces in lower inset show effect of 80 μM S-(+)-14 on 1 mM GABA currents.