Effects of 400 µM isoflurane on the activity of inositol trisphosphate receptor (InsP₃R) channel in various [InsP₃]. (A–D) Typical single-channel current traces of InsP₃R channels in various [InsP₃] in the absence and presence of 400 μM isoflurane, as indicated. Currents shown were recorded at room temperature with applied potential (V_app) = −40 mV, and arrows indicate the closed channel current level. See figure 1, A–C, for InsP₃R channel current traces in 0, 1, and 10 μM InsP₃ with no isoflurane, and figure 1D for InsP₃R channel current trace in 400 μM isoflurane only. (E) Statistically similar InsP₃R channel activities (P > 0.05, ANOVA test) were observed in 100 nM ≤ [InsP₃] ≤ 1 μM in the absence of isoflurane. With 400 μM isoflurane, statistically similar InsP₃R channel activities (P > 0.05, ANOVA test) were also observed in 0 ≤ [InsP₃] ≤ 1 μM. Importantly, 400 μM isoflurane significantly increased InsP₃R channel activity at low [InsP₃] (0, 100, and 500 nM). Error bars indicate SEM, and number of experiments analyzed is tabulated. **, *P (t test) <0.005 and 0.05, respectively, for the quantities connected by the brackets. InsP₃R channel P_o in saturating 10 μM InsP₃ were significantly higher (P < 0.05, t test with Bonferronic correction) than those in subsaturating [InsP₃], in the presence or absence of 400 μM isoflurane. However, InsP₃R channel activity in saturating (10 μM) InsP₃ was not enhanced by 400 μM isoflurane (P > 0.05, t test).