Figure 2. Frequency–current (F–I) and current–voltage (I–V) relations.

A, the cell responded to a slow-depolarizing current ramp (bottom trace) with sustained repetitive firing (top trace). B, the F–I relation (ascending ramp only) is plotted for the cell in A. The slope of the linear regression (black line) defined the F–I gain for the cell. C, a slow-depolarizing voltage-ramp command (bottom trace) was used for all voltage-clamp protocols. The current response in control conditions (black line) and in the presence of 1 μm TTX (grey line) is shown. D, the I–V relations (ascending ramp only) for the control (black trace) and TTX (grey trace) trial are shown. Na_P was measured as the difference between these two I–V functions.