Differential effects of F6 on heterotrimeric α5β3γ2L GABAA receptors. A. In contrast to its inhibition of heterodimeric receptors, 16 μM F6 (middle trace) did not block responses to 1 mM GABA (top), but it did enhance responses to 1 μM GABA (bottom) mediated by heterotrimeric receptors B. Concentration response relationships for α5β3γ2L receptors in the absence (squares, EC50 = 10.8 μM, slope = 0.68, n = 5–13) and presence (circles, EC50 = 4.7 μM, slope = 0.45, n = 3–8) of F6 (mean ± S.E.M). C. F6 had no effect on the time course of desensitization or deactivation. Normalized whole cell responses to 20 ms pulses of 1 mM GABA in the absence and continuous presence of F6 (16 μM).