Figure 4.

The effects of chlordiazepoxide, allopregnanolone and pentobarbitone on the concentration-response curves of THIP for α₃β₃γ₂ GABA_A receptors. (a) Example recording of currents in response to THIP in the absence and presence of 30 μM chlordiazepoxide, showing control responses to a saturating concentration of GABA (3 mM) after each concentration-response curve. Drugs were applied as indicated by the bars. (b) Mean concentration-response curves to THIP in the absence and presence of 30 μM chlordiazepoxide, 100 nM allopregnanolone and 50 μM pentobarbitone. Chloride currents are expressed as per cent of the peak current elicited by 3 mM GABA. Data are mean±s.e.mean of 3–6 experiments. (c) The effects of chlordiazepoxide on the chloride currents elicited by a maximally effective concentration (3.3 mM) of THIP for α₃β₃γ₂ GABA_A receptors. Data are mean±s.e.mean of five experiments. Chloride currents are expressed as per cent of the peak current elicited by 3 mM GABA. 3.3 mM THIP alone elicited 25±5% of the current peak for 3 mM GABA. It was enhanced by chlordiazepoxide with an EC₅₀ value of 6 (3,11) μM and a Hill slope value of 0.64 (0.57, 0.71).