Fig. 2. Concentration-response relationships for acetylcholine-induced currents in the absence and presence of isoflurane, sevoflurane, and halothane. The anesthetics were coapplied with acetylcholine. ( A ) Isoflurane at 100 μm inhibited peak current at all acetylcholine concentrations tested. ( B ) Acetylcholine concentration-response curves in the absence (○) and presence of 100 μm (0.36 MAC) isoflurane (•), 132 μm (0.4 MAC) sevoflurane (□), and 92 μm (0.4 MAC) halothane (▪). The data points are the mean peak currents expressed as percentages of the control current, and the error bars are standard deviations (n = 5). Sevoflurane and isoflurane decreased the apparent affinity for acetylcholine of the receptor by increasing the acetylcholine EC50from the control of 11.8 μm to 26.0 μm and 55.9 μm, respectively, with little or no change of Hill coefficients (0.7 to 0.6, 0.6). Halothane not only decreased the apparent affinity for acetylcholine by increasing the acetylcholine EC50from the control of 11.8 μΜ to 55.3 μΜ but also decreased the maximum response. ( C ) Inhibition by isoflurane, sevoflurane, and halothane at various concentrations of acetylcholine. The current amplitude in terms of the percentage of the control increased with the increasing concentration of acetylcholine.