Figure 2. pTFD-di-iPr-BnOH is a positive allosteric modulator of α1β3γ2L GABA_ARs.

A. pTFD-di-iPr-BnOH enhances the specific binding of both [³H]muscimol and [³H]flunitrazepam to α1β3γ2L receptors in HEK293 cell membranes as described in Methods. The [³H]muscimol data points and their standard deviation are calculated from six separate experiments, forty four individual points, each of whose maximum modulation was normalized to one; the EC50 = 7.4 ± 0.6 μM, n_H = 1.9 ± 0.3. The eighteen [³H]flunitrazepam data points are individual points from two independent experiments; EC50 = 11 ± 1 μM, maximum enhancement = 198 ± 4% and n_H = 2.7 ± 1.0. B. pTFD-di-iPr-BnOH enhances 3 μM GABA (~EC₀₂) currents in α1β3γ2L GABA_ARs expressed in oocytes. The displayed points are the means and SD of five oocytes; EC50 = 10 ± 1 μM, maximum enhancement = 30 ± 1–fold and n_H = 2.0 ± 0.4 (n = 33). C. The concentration-response curves for GABA–stimulated currents normalized to the current at 1 mM GABA are plotted in the absence and presence of 4 μM pTFD-di-iPr-BnOH. For GABA alone the EC50 = 58 ± 5 μM, n_H = 1.0 ± 0.1 (n = 33). For GABA at fixed pTFD-di-iPr-BnOH the EC50 = 11 ± 2 μM, the n_H = 0.8 ± 0.1 (n = 40). All curves are nonlinear least squares fits of the individual data points to equations 1 or 2. Means and SD are shown for display purposes.