Pharmacological modulation of GABA responses at α4β1δ receptors by various inhibitors and the neurosteroid, THDOC. A, Representative membrane currents showing inhibition of GABA (EC75) by 1 μM Zn2+ at α4β1 (upper) and α4β1δ (lower) receptors. B, Zn2+ concentration-inhibition relationships for α4β1 (n = 6) and α4β1δ (n = 6) receptors. C, Representative currents showing the degree of desensitization when activated by EC75 GABA in the absence (upper) and presence (lower) of 1 μM Cu2+. D, Cu2+ concentration-inhibition relationship for GABA EC75 desensitized responses at α4β1δ receptors by increasing concentrations of Cu2+ (n = 12). E, SCS concentration-inhibition relationship for GABA EC20 peak responses at α4β1δ receptors by increasing concentrations of SCS (n = 4). F, Response of α4β1δ receptors to increasing concentrations of THDOC co-applied with an EC7 GABA concentration. The responses were normalised to a preceding application of GABA EC7 in the absence of THDOC (n = 9). All data shown are means ± SEMs.