Figure 1.

TEA⁺ irreversibly abolishes I_K without affecting I_Na when external K⁺ is absent. (A) Membrane potential was stepped from −110 mV to 40 mV. In the trace labeled Before TEA, the voltage jump resulted in an outward Na channel gating current (I_g), immediately followed by an inward Na current (I_Na). I_Na inactivated leaving the slower activating outward potassium current (I_K). Internal perfusion with 20 mM TEA⁺ completely blocked I_K and reduced I_Na without affecting I_g (trace labeled In 20 mM TEA⁺). After washout of TEA⁺, which was applied for 5 min, I_Na fully recovered while I_K remained absent (trace After TEA). (B) Time course of peak amplitudes of I_K and I_Na of the experiment in A. Stable I_Na and I_K can be recorded for long periods of time without significant decline in their amplitudes. Perfusion of 20 mM TEA⁺ completely blocked I_K and reduced I_Na. Upon washout of TEA⁺, I_Na fully recovered, but I_K remained absent. Experiment SE126A. (C) To test whether the irreversible effect of TEA⁺ on I_K requires the opening and closing of K channels, an axon was clamped at −110 mV and perfused with 2 mM TEA⁺ (solid bars) with and without repeated 10-ms depolarizing pulses to 20 mV. I_K fully recovered when no pulses were applied. Less than 45% recovered when the axon was repeatedly depolarized in the presence of TEA⁺. I_Na was not affected by either procedure. Experiment Au276A.