Fig. 2. Irreversible effects of photo-activated azi-etomidate on γ-aminobutyric acid type A (GABA^A) receptors expressed in  Xenopus oocytes and human embryonic kidney cells. (  A ) Average (±SD) ratio of currents elicited with 10 μm GABA (I¹⁰)  vs. 1 mm GABA (I¹⁰⁰⁰) for six groups of oocytes expressing α¹β²γ^2Lreceptors. The number of cells in each group is shown inside the  bar , and factors included during a 5-min oocyte pretreatment are indicated below: ND96 is electrophysiology buffer; +UV = 365 nm light/−UV = room light; Azi-Eto = 3.2 μm azi-etomidate; GABA = 10 μm GABA. Oocytes were washed extensively (see “Materials and Methods”) after treatment. Only cells exposed to UV light, azi-etomidate, and GABA displayed significantly enhanced responses to low GABA. * Differs from control (ND96 –UV) at  P < 0.05. (  B–E ) HEK 293 cells on coverslips were exposed to azi-etomidate and UV light in culture dishes, followed by extensive washing (see “Materials and Methods”). (B) GABA-activated currents were recorded from a cell after exposure to 365 nm light for 5 min. GABA concentration is indicated in micromolar, and the  bar over the traces indicates GABA application. I¹⁰/I¹⁰⁰⁰= 0.12; deactivation τ^w(weighted average time constant for deactivation) = 50 ms. (  C ) GABA-activated currents were recorded from a cell after exposure to 10 μm azi-etomidate + 10 μm GABA + 365 nm light for 5 min, then washed for 10 min. I¹⁰/I¹⁰⁰⁰= 0.52; deactivation τ^w= 320 ms. (  D ) Average normalized (to 1 mm GABA control) GABA-induced peak currents from HEK293 cells and patches after no treatment (  circles , five cells; EC⁵⁰= 46 ± 4.4 μm) or photo-modification with 3.2 μm azi-etomidate + 10 μm GABA + 365 nm light for 5 min, then washed for 10 min (  triangles , six cells; EC⁵⁰= 17 ± 6.3 μm). (  E ) I¹⁰/I¹⁰⁰⁰data from HEK293 cells after various 5-min treatments and subsequent washing. Treatment conditions are indicated below each  bar , and the number of cells is indicted in each  bar : ECF = electrophysiology buffer; UV = 365 nm light; Azi = 3.2 μm azi-etomidate; GABA = 10 μm GABA; Eto = 100 μm etomidate. * Differs from ECF control at  P < 0.05. ** Differs both from ECF control and from Azi + GABA + UV at  P < 0.01.