Fig. 5.

Slowly inactivating currents have pharmacological properties similar to those of the slowly deactivating currents. A, Currents evoked by the voltage-clamp protocol shown at the top. The protocol was applied each 40 sec. The thin lines show currents evoked with a prepulse to 0 mV. The protocol was applied in the presence of 0.3, 1, and 10 mm TEA. B, Semilogarithmic plot of the current, obtained by stepping from −60 to 0 mV. The solid line shows the exponential fit of the slow component of the data; the time constant was 3.4 sec. C, Inactivating fraction of the current at +40 mV. This current was obtained by subtracting the currents evoked by the step to +40 mV without and with the 10 sec prepulse to 0 mV. D, A graph depicts the normalized amplitude of the block by TEA of the inactivating current shown in C. It was assumed that 0.3 mm TEA leaves the same fraction of inactivating current as seen Figure 2,D and E.