Figure 1.

Diazepam increases THIP and P4S potencies and efficacies at α1β2γ2S receptors. A, Left, Membrane currents activated by 1 mm P4S in the absence, presence, and after recovery from potentiation by 1 μm diazepam (DZ). Bars indicate durations of drug application. Right, Pooled data for the potentiation by 1 μm diazepam of currents activated by 1 mm GABA (n = 6), 1 mm P4S (n = 11), 10 mm P4S (n = 5), and 10 mm THIP (n = 4). Control current amplitudes = 1. B, Concentration–response curves for GABA (black), THIP (red), and P4S (blue) under control conditions (open symbols, solid lines) and in the presence of 1 μm diazepam (filled symbols, dotted lines). Curves were generated from the Hill equation for GABA in control (I_max normalized to 1; EC₅₀ = 153 ± 22 μm; n_H = 0.84 ± 0.02; n = 5) and in 1 μm diazepam (I_max normalized to 1, see Materials and Methods; EC₅₀ = 35 ± 15 μm; n_H = 0.85 ± 0.05; n = 4). For THIP in control (I_max = 0.77 ± 0.04; EC₅₀ = 834 ± 154 μm; n_H = 1.09 ± 0.03; n = 4) and in 1 μm diazepam (I_max = 0.87 ± 0.03; EC₅₀ = 314 ± 85 μm; n_H = 0.93 ± 0.11; n = 4); and for P4S in control (I_max = 0.27 ± 0.03; EC₅₀ = 185 ± 30 μm; n_H = 0.86 ± 0.02; n = 5) and in 1 μm diazepam (I_max = 0.51 ± 0.07; EC₅₀ = 63 ± 13 μm; n_H = 0.90 ± 0.01; n = 4).