Fig. 2. (A) Upper trace: fast inactivating potassium current recorded after inhibition of the delayed potassium current by tetraethyl ammonium. Lower trace: voltage steps applied to the membrane. Horizontal bar, 1 ms; vertical bars, 0.1 nA (top) and 40 mV (bottom). (B) Upper trace: fast inactivating potassium current recorded after inhibition of the delayed potassium current by tetraethyl ammonium. Lower trace: inhibition of the fast inactivating potassium current by 4-amino pyridine. Horizontal bar, 1 ms, vertical bar, 0.1 nA. (C) Inhibition of the fast inactivating potassium current by depolarizing pulses applied to the membrane before the test pulse. Horizontal bar, 1 ms, vertical bar, 0.1 nA. (D) Inhibition curve of the I_K fast current by depolarizing pulses. Experimental points are fitted onto a Boltzman-type equation. Vertical: normalized current expressed as measured current/maximum measured current. Horizontal: depolarizing pulse expressed as minus the pipette voltage V_pip.