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. 2014 Nov 24;171(23):5446–5457. doi: 10.1111/bph.12861

Figure 3.

Figure 3

3α5βP affects etomidate concentration–response properties in the absence and presence of GABA. (A) Concentration–response curves for gating by etomidate in the absence and presence of 1 μM 3α5βP. The data were normalized to the response to a saturating concentration (100 μM) of GABA in the same cell. The data points give mean ± SEM from five cells in each condition. The data were fitted as described in Methods. The results (best fit±uncertainty estimate) from the fits are as follows. Control: EC50 = 218 ± 5 μM, Hill coefficient, n = 2.5 ± 0.1, Ymax was constrained to an arbitrarily chosen value of 0.9 and Ymin was constrained to 0. The data point at 1000 μM is skewed by channel block, and was not included in the fit. Etomidate +1 μM 3α5βP: EC50 = 2.8 ± 0.5 μM, n = 1.4 ± 0.3, Ymax = 0.98 ± 0.04, Ymin = −0.01 ± 0.07. (B) Sample current response traces from HEK 293 cells expressing rat α1β2γ2L GABAA receptors activated by 0.5 μM GABA, 1 μM etomidate or 100 nM 3α5βP, or by combinations of these drugs. The bar on top of current traces indicates the duration of drug application. The data show that the application of GABA + etomidate + 3α5βP potentiates the current responses beyond what is seen with applications of single drugs or any combination of two drugs. The inset shows current traces in the presence of GABA, etomidate or 3α5βP, at a higher resolution. (C) Concentration–response curves for etomidate in the presence of 0.5 μM GABA, GABA + 100 nM 3α5βP or GABA + 1 μM 3α5βP. The data were normalized to the response to 100 μM GABA. The data points give mean ± SEM from five cells under each condition. The data were fitted as described in Methods. The results from the fits are as follows. Control (etomidate + 0.5 μM GABA): EC50 = 2.0 ± 0.1 μM, n = 1.6 ± 0.2, Ymax = 0.86 ± 0.02, Ymin = 0.03 ± 0.02. Etomidate + 0.5 μM GABA + 100 nM (1 μM) 3α5βP: EC50 = 0.71 ± 0.05 μM, n = 1.0 ± 0.1, Ymax = 1.04 ± 0.06, Ymin was constrained to the response obtained in the presence of 100 nM 3α5βP + 0.5 μM GABA (0.03). Etomidate + 0.5 μM GABA + 100 nM (1 μM) 3α5βP: EC50 = 0.28 ± 0.06 μM, n = 0.9 ± 0.2, Ymax = 0.96 ± 0.04, Ymin was constrained to the normalized response obtained in the presence of 1 μM 3α5βP + 0.5 μM GABA (0.21).