Figure 2. Na currents in BCs show negative shift of inactivation sensitivity and low current density. A, Measuring Na channel activation in nucleated patches from a representative SC (i) and BC (ii). Top traces represent the voltage command, which was stepped from −120 mV to Vstep between −110 and −20 mV. Bottom traces represent recorded Na currents. iii, iv, TTX abolished remaining current, confirming it is Na current. B, Peak Na current for the SC in Ai and BC in Aii for different Vstep. C, Normalized conductances calculated from curves in B. D, Measuring Na channel inactivation from a representative SC (i) and BC (ii). Top traces represent the voltage command, which was held at Vhold from −150 to −20 mV and stepped to 0 mV. E, Normalized conductance as a function of Vhold for the cells in D. F, Average activation curves from 14 SCs (closed circles) and 15 BCs (open circles). Data were fit with a Boltzmann function: g/gmax = 1/{1 + exp[(V1/2act − V)/kact]}, with V1/2 = −33.0 mV, k = 7.1 mV for SCs and V1/2 = −31.5 mV, k = 8.1 mV for BCs. G, Average inactivation curves from 14 SCs (closed circles) and 15 BCs (open circles). Data were fitted with a Boltzmann function, with V1/2 = −75.4 mV, k = −12.1 mV for SCs and V1/2 = −87.7 mV, k = −13.9 mV for BCs. H–N, Comparisons of BCs and SCs. Plots are cumulative histograms of data from individual patches, and markers at the top are mean ± SEM. H, Half-activation voltages. I, Half-inactivation voltages. J, Maximal Na current amplitudes. K, Membrane capacitance of nucleated patches. L, Maximal Na current densities from data in J and K. M, N, The Na current densities available at −70 mV (M) and −60 mV (N).