Figure 1.

Voltage-dependent gating of MthK. (A) Representative inward current through a single MthK channel in symmetrical 200 mM KCl, with 20 mM Ca²⁺ at the cytoplasmic side of the channel. At negative voltages, Po decreases slightly with increasing hyperpolarization because of the increased frequency of brief (flicker) closings, as described previously (Zadek and Nimigean, 2006). (B) Outward current through the same MthK channel under the same ionic conditions. Po decreases strongly with increasing depolarization because of increases in both the duration and frequency of closings. (C) Mean Po versus voltage. At positive voltages, the Po versus voltage relation is described by a single Boltzmann equation (solid line; refer to Materials and methods) with a V_1/2 of 96 mV and gating valence (zδ) of 1.4 e₀. (D) Raw mean closed times (filled squares) deviated slightly from a simple exponential voltage dependence, but were fitted well by a single exponential after the application of a correction for missed events (open circles, corrected data; dashed line, exponential fit). (E) Likewise, mean open times (filled squares) deviated from a simple exponential voltage dependence, but this too could be accounted for after correction for missed events (open circles, corrected data; dashed line, exponential fit).