A, frequency dependence of WT-SCN1A and ICEGTC mutants. Cells were stimulated with depolarizing pulse trains (100 pulses, 5 ms, 0 mV) from a holding potential of −120 mV at the indicated frequencies. A recovery interval (15 s, −120 mV) followed each pulse train experiment. Currents were normalized to the value recorded after the first pulse in each frequency train for the corresponding allele and plotted on a log scale. Data are means ± s.e.m. from 3 or 4 cells. Significant differences (P < 0.05) from WT-SCN1A were observed for V983A (40–80 Hz), V1611F (60–80 Hz) and F1808L (50–80 Hz). B, residual normalized sodium current after the 60th pulse during a 60 Hz pulse train (n = 5–7 cells). Significant differences from WT-SCN1A are indicated as *P < 0.05 and **P < 0.005.