Fig. 2. 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 holding potential of −70 mV 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) for control (  open symbols ) and 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 but otherwise did not change the current-voltage relationship. (  B ) Activation curves (mean ± SEM, n = 6–10) for TTX-r Na^v1.8 and TTX-s Na^vconductance in the absence (  open symbols ) or presence (  closed symbols ) of isoflurane. The data show the normalized Boltzmann function for conductance (  G /  G ^max) derived from the equation;  G /  G ^max= 1/[1 + exp(V^1/2− V/  k ), where  G is the measured conductance,  G ^maxis the maximal conductance, V^1/2is the membrane potential for half-maximal activation, and  k is the slope.