TABLE 2

Sedative/anticonvulsant inhibition and enhancement (+bicuculline) of α1β3γ2 GABAAR photolabeling by [3H]azietomidate and [3H]R-mTFD-MPAB

When drugs only inhibited photolabeling, data were fit to eq. 1 (Materials and Methods) to determine IC50, the total drug concentration producing 50% inhibition of GABAAR photolabeling, and Hill coefficients (nH) and, when indicated, to eq. 2, a two-site model. For inhibition in the presence of bicuculline, nH was set to 1. When enhancement was seen in the presence of bicuculline, data were fit to eq. 3B, as noted in the figure legends, to determine EC50 and IC50 values for 50% maximal enhancement and inhibition. Parameters (best fit ± S.E.) were determined from fits of data from N independent experiments, using two or more GABAAR purifications. As bicuculline and GABA experiments were paired, their values of N are the same.

Drug (NR-mTFD-MPAB, Naziet)Ratio IC50(AziEt)/IC50(R-mTFD-MPAB)a[3H]R-mTFD-MPAB IC50 (nH)[3H]R-Azietomidate IC50 (nH)
+GABA+GABA+Bicuculline EC50/IC50+GABA+Bicuculline EC50/IC50
μMμMμMμM
TG-41 (4, 3)0.2 ± 0.10.10 ± 0.04 (1) Bns = 67% ± 2%eq. 3B 0.02 ± 0.007/0.4 ± 0.20.016 ± 0.003 (1)0.22 ± 0.06
Loreclezole (4, 4)b6c116 ± 35 (0.43 ± 0.06) eq. 2 IC50H = 1.4 ± 1.2 (29% ± 7%)/IC50L = 320 ± 120eq. 3B 2.5 ± 0.8/160 ± 309.3 ± 0.9 (1.2 ± 0.1)44 ± 30
Tracazolate (6, 3)0.4 ± 0.218 ± 7 (1) Bns = 56% ± 5%eq. 3B 2.7 ± 0.6/24 ± 58.0 ± 0.9 (1.0 ± 0.1)18 ± 7
Stiripentol (3, 3)2 ± 0.462 ± 7 (1.7 ± 0.3)73 ± 39134 ± 14 (1.8 ± 0.3)70 ± 14/84 ± 14
  • a For the ratio of IC50 values (+GABA), uncertainties were determined by propagation of error from the individual parameter uncertainties.

  • b For loreclezole inhibition of [3H]R-mTFD-MPAB photolabeling (+GABA), parameters are also included for the fit of the data to a two-site model, eq. 2.

  • c The ratio calculated for the high-affinity component (IC50H) for inhibition of [3H]R-mTFD-MPAB photolabeling.