Figure 2.

Extracellular K⁺ ions protect K channels against the irreversible effect of TEA⁺. (A) Time course of maximum I_K amplitudes after voltage jumps to 40 mV. The axon was bathed in a solution containing 20 mM K⁺ ions and perfused with 1 mM TEA⁺ (open bar) for 5 min. I_K was reduced to ≈40% of its peak by TEA⁺ and almost fully recovered when TEA⁺ was washed out. I_K also fully recovered from TEA⁺ when the extracellular solution contained 10 mM K⁺. When no K⁺ was added to the extracellular solution, however, less than 20% of the current recovered after exposure of the axon to TEA⁺. Experiment SE136A. (B) The rate of disappearance of K channels can be followed in the absence of extracellular potassium ions. I_K amplitude is plotted on logarithmic scale, immediately after perfusion with 1 mM TEA⁺ in the presence (open circles) and absence (filled circles) of 20 mM TEA⁺. In both cases the amplitude of I_K initially decreases rapidly and to the same extent as the channels are blocked by TEA⁺ (first two points). Once TEA⁺ had equilibrated, I_K remained stable in the presence of 20 mM K⁺ outside, but it decreased exponentially in the absence of K⁺.