Etomidate and etomidate analog concentration-response curves for inhibition of specific ³[H]azi-etomidate (A) and tritiated R-5-allyl-1-methyl-5-(m-trifluoromethyl-diazirynylphenyl) barbituric acid (R-³[H]mTFD-MPAB; B) photolabeling of α₁β₃γ_2L γ-aminobutyric acid (GABA) type A receptors. Each curved line is a fit of the dataset to equation 2. Each symbol is the mean ± SD derived from three or four separate experiments. Data were normalized to counts per minute measured in the absence of competing ligand. Nonspecific photolabeling was defined in the presence of 300 µM etomidate (for ³[H]azi-etomidate photolabeling experiments) and either 60 µM or 100 µM R-5-allyl-1-methyl-5-(m-trifluoromethyl-diazirynylphenyl) barbituric acid (for R-³[H]mTFD-MPAB photolabeling experiments). All photolabeling was done in the presence of 300 µM GABA to stabilize receptors in the open/desensitized state.