Figure 3.

MthK is sharply activated by Ca²⁺ in the millimolar range. (A) Representative single-channel traces at 0, 3.5, 4, and 5 mM Ca²⁺. (B) Ca²⁺ dose–response of MthK. Each open symbol is a single bilayer, with 11 different bilayers analyzed. Filled symbols represent mean ± SEM from three separate bilayers with the exception of the 10 mM Ca²⁺ point with n = 2. Data points were fit with the Hill equation (Eq. 3) with n = 8 (smooth line, K_d = 3.8 ± 0.2 mM, and r_a,max = 1.07 ± 0.1) and n = 20 (dashed line, K_d = 3.8 ± 0.04 mM, and r_a,max = 1.00 ± 0.04). Inset shows a Ca²⁺ dose–response from a single representative bilayer. The data (open circles) were fit with the Hill equation with n = 8 (K_d = 3.9 ± 0.14 mM, and r_a,max = 1.08 ± 0.14). The axes are the same as in B.