KCa3.1 current activation requires unexpectedly high intracellular free Ca²⁺.

<p>For these experiments on MLS-9 cells, the bath contained 100 nM apamin to eliminate any possible contribution of SK3. <b>A.</b> The two traces (same voltage protocol as in <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0062345#pone-0062345-g001" target="_blank">Fig 1</a>) show a small current immediately after establishing the whole-cell recording (0 min) and 3 min later. The pipette solution contained 10.9 µM free Ca²⁺. <b>B, C.</b> The time course of the current measured at +80 mV is shown for two cells with 10.9 µM free intracellular Ca²⁺. The cell in panel A is shown in B. For a different cell (panel C), the KCa3.1 blocker, 1 µM TRAM-34, was added to the bath after the current reached a plateau, and then washed out with standard bath solution. <b>D.</b> Ca²⁺-dependence of KCa3.1 current activation. The current density (pA/pF) as a function of intracellular free Ca²⁺ is fitted to the Hill equation. The maximal current density is indicated by the dashed line, and the EC₅₀ is indicated by the vertical arrow.