Figure 1. Activation of I_Na in HEK cells assessed with square-step voltage protocols in conventional VC experiments.

a, Top: Typical examples of Na⁺ current in response to depolarizing voltage steps from −140 mV. Bottom: Average fast and slow time constants of Na⁺ current inactivation. Note logarithmic ordinate scale. b, Average current-voltage relationship. c, Average steady-state activation. The solid line is the Boltzmann fit to the average data. d, Typical membrane depolarizations in response to a super- and subthreshold current pulse in a HEK cell during an alternating VC/CC experiment from a holding potential of −140 mV (top) and the first derivatives of the resulting membrane potential changes (dV/dt; bottom).