Figure 4. Voltage dependence of activation and inactivation.

A, currents of a human DGC elicited by the activation protocol shown in the inset. The extracellular Na⁺ concentration was 163 mm. The current amplitude was reduced with 10 nm STX. B, mean values of the normalized conductance of 4 DGCs. The smooth curve through the data points was calculated from the mean values of the parameters obtained by fitting a modified Boltzmann function to the data points, with k_m= 5.9 ± 0.4 mV and $V_{50}^{\text{m}}=-29\pm 4\text{mV}$ (for comparison, see Fig. 1B). C, steady-state voltage-dependent inactivation of Na⁺ currents in a human DGC measured with test pulses to -17 mV following 100 ms conditioning prepulses that were incremented by 10 mV steps from -117 to -27 mV. The prepulses were preceded by a 100 ms pulse at -107 mV to remove slow inactivation. D, conductances were obtained from the peak currents, normalized and fitted with the Boltzmann equation (eqn (2), with $V_{50}^{\text{m}}$ and k_m replaced by $V_{50}^{\text{h}}$ and k_h, respectively). The voltage of half-maximal inactivation, $V_{50}^{\text{h}}$, was -55 ± 2 mV, and k_h was -5.6 ± 1.1 mV (n= 3). The dotted line shows the fitted activation curve from B.