Fig. 3.

K⁺ currents in a sustained-regular cell. A, Voltage-clamp recordings of outward currents in a sustained-regular cell in the presence of 2 μm TTX. The cell was held at −60 mV and stepped to +40 mV in 5 mV increments. B, Instantaneous K⁺ current amplitudes, measured 50 msec after the start of the voltage step in external saline containing normal Ca²⁺ (2.4 mm) and low Ca²⁺ (0.1 mm). C, K⁺ currents, recorded in TTX, with and without the addition of 2 mm 4-AP. Top trace, Total current in TTX; bottom trace, current remaining after addition of 2 mm 4-AP; middle trace, the 4-AP-sensitive current obtained by subtracting the bottom trace from the top trace. D, Plot of the steady-state K⁺ current amplitude as a function of the voltage level during voltage-clamp recordings. Mean ± SEM of seven cells. E, K⁺ currents plotted for a voltage range corresponding to the dynamic range of the cell. 4-AP I_K, 4-AP-sensitive K⁺current; res I_K, current insensitive to 4-AP. Mean ± SEM of the same seven cells shown inD. F, Plot of the firing frequency as a function of the peak amplitude of the 4-AP-sensitive K⁺ current, both being recorded at similar membrane potentials, corresponding to the dynamic range of the cell.