Persistent Na⁺ conductance in soma and AIS behaves as a Boltzmann function of the voltage. A, Mean I_NaP density in soma (black) and AIS (red) obtained by time-based differentiation of the Na⁺ charge transfer traces with respect to time for soma (n = 8), and by digital subtraction of the rates of diffusional Na⁺ outflow from the influx rates measured in AIS (n = 12). B, Persistent Na⁺ conductance density in soma (black) and AIS (red) as a function of voltage. Continuous lines are the best fits by a Boltzmann equation (V1/2 = −42 and −52 mV for soma and AIS, respectively). C, Somatic (black) and AIS (red) contribution for total (blue) persistent sodium current in response to voltage ramp from −70 to +10 mV. Currents are calculated based on I_NaP density and surface area of the compartments.