Figure 5.

Mes V neurons show resurgent sodium currents. A1, The top trace shows voltage protocol, and the bottom trace shows current response. I_NaT was evoked by a 3 ms step pulse from −90 to +30 mV. TTX-sensitive I_NaR was elicited when the membrane was repolarized to voltages between −70 and −10 mV after maximal fast inactivation. The data have been expanded for clarity, and the break in time is 10 ms. A2, TTX-sensitive sodium current was obtained by applying a slow ramp (−90 to +30 mV; 100 mV/s) followed by a step repolarization to −40 mV. I_NaR is evident after repolarization to −40 mV (arrow). The inset shows the expanded timescale of the boxed region in which I_NaR is present. B, TTX-sensitive I_NaR properties are voltage dependent. Relationships between peak I_NaR (top), rise time (middle), and decay time (bottom) versus repolarization command potential are shown. Error bars indicate SD. C, Relationship between resurgent sodium current components and total sodium current. The hybrid waveform protocols are shown on the top, and the current traces are shown below. Solid black is total sodium current evoked by template action potential, and the gray trace is current in response to a step pulse (3 ms) to inactivate I_NaT followed by the repolarization phase of the action potential. The isolated I_NaR (gray) was superimposed with the total sodium current (black). Note that these two traces overlapped at the peak of the AHP and for some time thereafter.