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. 2003 May;121(5):375–398. doi: 10.1085/jgp.200208746

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Copyright © 2003, The Rockefeller University Press

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Figure 6. — Dwell time distributions of discrete blocking events associated with slow block by external Ba²⁺ compared for PE and PS bilayers. (A and B) Dwell time histograms compiled for a single BK channel in a PE membrane recorded at 20 mV in the presence of symmetrical 100 mM KCl, 10 mM HEPES-KOH, pH 7.2, internal 200 μM CaCl₂, and external 20 mM BaCl₂. Populations of unblocked (A) and blocked (B) events were kinetically isolated from normal gating events by filtering the record at 10 Hz (Vergara and Latorre, 1983) and using PClamp analysis software to automatically compile blocked and unblocked events using a 50% threshold criterion for event detection. The solid line in A is a fit to a single exponential with a lifetime of 623 ms for a population of 585 events. The solid line in B is a fit to a sum-of-two exponentials with lifetimes (amplitudes) of 206 ms (68%) and 6.84 s (32%) for 585 events. (C and D) Examples of blocked time histograms are compared for PE (C) and PS (D) bilayers at 2, 6, and 20 mM external Ba²⁺. The solid lines are fits to a sum of two exponentials with respective lifetimes (amplitudes) at 2, 6, and 20 mM Ba²⁺ for PE (C): 850 ms (82%), 2.97 s (18%); 94 ms (81%), 2.65 s (19%); 115 ms (77%), 2.7 s (23%), and for PS (D): 85 (79%), 2.1 s (21%); 105 ms (75%), 3.6 s (25%); 104 ms (74%), 3.5 s (26%).