Fig. 4. Submaximal γ-aminobutyric acid (GABA) currents in the wild-type α2β3γ2s receptor are also strongly enhanced by sevoflurane and desflurane, but not in α2(S270I)β3γ2s. (A ) Representative examples of enhancement of submaximal GABA responses by sevoflurane and desflurane. Sample tracings were obtained from human embryonic kidney cells expressing the wild-type α2β3γ2s receptor (top ) and mutant receptor, α2(S270I)β3γ2s (bottom ). The anesthetics were preapplied for 3 s before coapplication with submaximal concentration (EC20) of GABA (3 μm for the wild-type and 0.7 μm for mutant receptor). In contrast to the wild-type α2β3γ2s receptor, submaximal GABA currents in α2(S270I)β2γ2s mutant receptor were not enhanced by coapplication of volatile anesthetics (up to 2 mm). (B ) Concentration-response relationships for potentiation of GABA-induced currents by three volatile anesthetics were summarized. Similarly, the EC50value for potentiation of α2β3γ2s receptor by isoflurane, sevoflurane, and desflurane was 0.28, 0.29, and 0.20 mm, respectively.