Fig. 6. Effects of isoflurane, halothane, and desflurane on voltage dependence of Na^v1.4 fast inactivation. (  A ) Representative traces show inhibition of  I ^Naby isoflurane (  left ), halothane (  middle ), and desflurane (  right ) using a fast inactivation protocol (  inset ) involving a conditioning pulse of 30 ms followed by a test pulse of 25 ms to minimize slow inactivation. Normalized data were fitted to the Boltzmann equation to yield voltage of 50% inactivation (  V^1/2in ) and slope factor for ∼1 minimum alveolar concentration (  MAC ) (B ) or ∼2 MAC (  C ). Each anesthetic significantly shifted the V^1/2inin the negative direction as determined by sum-of-squares F test comparison between curve fits of mean data (  P < 0.05). Parameters derived from analysis of independent curve fits are presented in  table 1. Anesthetic concentrations were 0.46 ± 0.09 mm and 0.82 ± 0.07 mm for isofluorane, 0.40 ± 0.06 mm and 0.77 ± 0.10 mm for halothane, and 0.82 ± 0.06 mm and 1.61 ± 0.07 mm for desflurane. Data are expressed as mean ± SEM, n = 5–7.