Fig. 7. Effects of isoflurane and halothane on recovery of Nav1.4 from fast inactivation. The protocol ( upper right inset ) involved 12 depolarizing test steps at various recovery times ( t ) in 2.5-ms intervals. Representative current traces obtained for the effects of isoflurane (2.3 minimum alveolar concentration [ MAC ]) and halothane (2.2 MAC) are shown on the right . The time-course of channel recovery from fast inactivation was best fitted by a monoexponential function in all cases to yield a recovery time constant ( τr ). The rate of recovery, expressed as current normalized to initial control current, was slowed by isoflurane ( A ) and halothane ( B ). The recovery time constant was greater for halothane than for isoflurane at the higher concentrations as determined by sum-of-squares F test between curve fits of mean data ( P < 0.001). Mean isoflurane concentrations were 0.44 ± 0.06 mm and 0.82 ± 0.08 mm; mean halothane concentrations were 0.41 ± 0.07 mm and 0.78 ± 0.10 mm. Data are expressed as mean ± SEM, n = 5–8. *** P < 0.001 versus . control.