Figure 11.

Ca²⁺ shifts the ΔG_O−C–V relations to lower energies. (A) Plot of ΔG_O−C vs. Ca²⁺ concentration for the BK_α (red) and BK_α+β1(blue) channels using the Ca²⁺ binding parameters determined from Fig. 11 (A and D). The plots were calculated using term 1 of Eq. 15. (B) As in Fig. 10 C, plotted here are the two model channel's ΔG_O−C–V relations in the absence of Ca²⁺. (C) The same relations now with 1 μM Ca²⁺, (D) 10 μM Ca²⁺, and (E) 100 μM Ca²⁺. The dashed lines in C, D, and E indicate the BK_α+β1 curve that would be observed, if there were no changes in Ca²⁺ bindng upon β1 coexpression. (F) Plotted are the total V_1/2 shifts predicted by the BK_α and BK_α+β1 model channels upon β1 coexpression at 0, 1, 10, and 100 μM Ca²⁺. In green is the percent of the total shift due to changes in voltage sensing, and in yellow is the percentage due to changes in Ca²⁺ binding.