Figure 12.

Dwell time distributions of discrete blocking events associated with slow block by internal Ba²⁺. Dwell time histograms were compiled as described in Fig. 6 for a single BK channel in a PE membrane at 20 mV in the presence of symmetrical 100 mM KCl, 10 mM HEPES-KOH, pH 7.2, internal 200 μM CaCl₂, and internal 100 μM BaCl₂. (A) Unblocked events. (B) Blocked events. The solid line in A is a fit to a single exponential with a lifetime of 222 ms for a population of 638 events. The solid line in B is a fit to a sum-of-two exponentials with lifetimes (amplitudes) of 127 ms (41%) and 2.73 s (59%) for 639 events.