Fig. 2. Current-voltage relationships and voltage-dependence of activation for tetrodotoxin-resistant (TTX-r) Nav1.8 ( left ) and tetrodotoxin-sensitive (TTX-s) Nav( 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 Nav1.8 and TTX-s Navconductance 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(V1/2− V/ k ), where G is the measured conductance, G maxis the maximal conductance, V1/2is the membrane potential for half-maximal activation, and k is the slope.