Figure 3.

MthK channel gating in the nominal absence of Ca²⁺. (A) MthK currents recorded from a single bilayer at pH 9.0; these currents are representative of several minutes of continuous recording at each of the indicated conditions. Here, in the presence of 5 mM EGTA, no openings were observed in 10 min of continuous recording, with the exception of the burst opening at the beginning of the second “5 mM EGTA” period (right). In addition, no openings were observed in 10 min of continuous recording with 0 added Ca²⁺ (no EGTA). Similar results were observed in two additional bilayers at pH 9.0 in the presence of 5 mM EGTA, and in six additional experiments at pH 9.0 with no added Ca²⁺ (no EGTA). (B) Po in the nominal absence of Ca²⁺, plotted as a function of pH. The dashed line represents a regression line fit with these data, which had a slope of 0.00017/pH unit and y intercept of −0.00098. These data are consistent with pH having little effect on Po in the absence of Ca²⁺. (C) Mean burst duration in the nominal absence of Ca²⁺, plotted as a function of pH. Increasing pH over the range of 7.3–9.0 did not yield a corresponding change in burst duration. The pooled burst durations over this pH range yielded a mean of 252 ± 46 ms (dotted horizontal line). (D) Mean gap duration in the nominal absence of Ca²⁺, plotted as a function of pH. Pooled gap durations over this pH range yielded a mean of 13.1 ± 4.7 min (dotted horizontal line).