Nav currents in CCs from FGF14 KO animals. (A) Currents from a WT mouse CC activated with the indicated protocol with colored traces as indicated. (B) Currents from an FGF14 KO CC. (C) Voltage dependence of current density for CCs from FGF14 KO mice (red points; 10 cells) and those from WT mice (18 cells). Mean ± SD. (D) Normalized G-V curves (see Materials and methods) for WT (from Fig. 1 D) and FGF14 KO cells. For WT, V_0.5 = −22.3 ± 0.3 mV with z = 5.3 ± 0.3e and, for FGF14 KO, V_0.5 = −17.2 ± 1.9 mV with z = 4.5 ± 0.1e. (E) Traces of Nav current activated at 0 mV from WT (black) and FGF14 KO (red) cells were averaged and fit with single exponential functions, with faster onset of inactivation in FGF14 KO cells. (F) Mean values (± SD) for onset of inactivation for WT and FGF14 KO cells are plotted as a function of command potential. P values adjusted for multiple comparisons (ANOVA with Bonferroni correction) for comparison of WT and FGF14 KO inactivation time constants over the range of 0 to +40 mV were all P < 0.01. (G) Steady-state inactivation curves (mean ± SD) following either a 1-s or 25-ms conditioning step are compared for CCs from WT and FGF14 KO mice. With a 1-s conditioning step, for WT, V_0.5 = −48.9 ± 1.0 mV; for FGF14 KO, V_0.5 = −57.3 ± 0.3 mV, while for a 25-ms conditioning step, for WT, V_0.5 = −35.6 ± 1.1 mV and, for FGF14 KO, V_0.5 = −47.2 ± 2.1 mV. (H) Measured voltage of half availability (mean ± SD of individual cells) following 25-, 100-, 250-, and 1,000-ms conditioning potentials are plotted for cells from WT (15 cells) and FGF14 KO (14 cells). For comparisons between WT and KO at each conditioning duration, P < 0.0001 (ANOVA with Bonferroni correction for multiple comparisons).