Fig. 3. Current-voltage relationships and voltage-dependence of activation for tetrodotoxin-resistant (TTX-r) Na^v1.8 (  left ) and tetrodotoxin-sensitive (TTX-s) Na^v(  right ) currents performed in the absence or presence of isoflurane. Whole cell currents were evoked from a hyperpolarized holding potential of −140 mV at which most Na⁺channels are in the closed resting state using a series of depolarizing steps from −80 mV to +70 mV in 10-mV steps (  inset ). Data are shown as mean ± SEM (n = 6–8) in the absence (  open symbols ) or presence of isoflurane (0.53 ± 0.06 mm, equivalent to 1.8 minimum alveolar concentration [MAC] when corrected to 24°C,  closed symbols ). (  A ) Isoflurane reduced peak current amplitude only minimally and did not change the shape of the current-voltage relationship. (  B ) Activation curves (mean ± SEM) for TTX-r Na^v1.8 and TTX-s Na^vconductance in the absence (  open symbols ) or presence (  closed symbols ) of 0.53 ± 0.06 mm isoflurane. See  Fig. 2 legend for details of curve fitting.