Comparison of the late component of Na⁺ current in the wild-type and ΔK1500 mutant Na⁺ channels. (a and b) The Na⁺ current was recorded at high gain (upper trace) and low gain (lower trace) with 200-ms pulses from a holding potential of –100 mV to a test potential of –20 mV. Currents were leakage-subtracted. The dashed lines show the 0 current level. (c) The average steady-state current (I_ss) is plotted as a function of the peak current (n = 4, hH1; n = 5, ΔΚ1500). (d and e) Single-channel currents recorded in cell-attached membrane patches with 200-ms pulses to a test potential of –20 mV with low-resistance microelectrodes. The upper four tracers in each panel show the responses to four consecutive trials. The lowest tracts show the average current. The dashed lines indicate the 0 current level.