Block of Ba²⁺ permeation by K⁺. Ba²⁺ block datasets were recorded as in Fig. 5, at different concentrations of external K⁺. (A) Nonconducting time histograms are shown (log-binned except for 10 µM K⁺ data, which is binned linearly to show its rising phase). (B) Behavior of fast/slow time constants (top) and amplitudes (bottom) of block-time distributions. Curves have no theoretical meaning, except for the 1/τ_s curve, which plots Eq. 7. Gray shading on the amplitude plot indicates the range of K⁺ concentrations where the fast amplitude, in reversing sign, becomes too small to observe and thereby produces a single-exponential block-time distribution.