Effect of external Na⁺ on leak currents and conductance in WT and V876E fibers. (A) Mean background current intensity measured at −80 mV in the absence and in the presence of external Na⁺ in WT and V876E fibers. Values were compared with paired tests and unpaired tests for data obtained within the same fiber population and for data obtained between the two fiber populations, respectively. P-values were 0.0001 and 0.0001 for comparison of the means between the Na⁺-free and the Na⁺ containing solution in WT and V876E fibers, respectively, and 0.047 for comparison of the means obtained in the presence of the Na⁺–containing solution in WT and V876E fibers. Data are given as means ± SEM. *, P < 0.05; ***, P < 0.0005. (B) Membrane currents evoked by a voltage ramp applied from a holding potential of −40 mV in the absence and in the presence of external Na⁺ in the same V876E fiber. (C) Means and SEM of current densities evoked by voltage ramps applied from a holding potential of −40 mV in the presence of external Na⁺ in WT fibers and V876E fibers. The number of data points has been reduced for clarity.