Fig. 6.

Tetraethylammonium (TEA) or 4-aminopyridine (4-AP) can block the slowly decaying transient current in patches. This figure shows traces from two exemplar patches. A₁, Control currents elicited by a step from −112 to +38 mV for 300 msec, followed by a 100 msec step to 0 mV (the voltage protocol is shown below A₁). The noisy tracerepresents data; the line is the best fit of the sum of two exponentials. A₂, Currents elicited in the presence of 10 mm TEA. Fast and slow decay components can still be discerned. Although the peak current is reduced, it is the slow component that is mainly responsible for the change [compare the amplitudes of the fast (a1) and slow (a2) components of the exponential fits].A₃, Subtraction of traces inA₁ andA₂ reveals the TEA-sensitive component of the current; this current is dominated by the slow component. B, Summary of inactivation as a function of prepulse voltages for the three conditions shown in A. The symbols correspond to those in A. The control inactivation curve (open squares) has a shallow slope and was fit with the sum of two Boltzmann functions. In the presence of TEA, half-inactivation is shifted to the negative by ∼20 mV (inverted triangles), whereas the TEA-sensitive current shows half-inactivation at more positive voltages (approximately −45 mV; open circles). C,D, Shown is the same experimental procedure as inA and B, except with 4-AP. The effects of 4-AP are similar to those of TEA, except for a slightly greater reduction of the fast component.