Figure 3.

Calmodulin mediates Ca²⁺ gating of SK channels. (A) Western blot prepared rom oocytes expressing the indicated CaM mutants. Samples were electrophoresed in loading buffer containing either Ca²⁺ (+) or EGTA (−), and the blot was probed with anti-calmodulin antibody. r, rat; WT, wild-type. (B) Ca²⁺ dose-response relation for SK2 channels expressed alone or with CaM(D_EF2,3,4A). Relative current amplitudes measured at -100 mV are plotted as a function of Ca²⁺ concentration. Lines represent a fit to the Hill equation to the data, yielding K_0.5 and Hill coefficient of 32 μM and 5.1 for SK2, and 2.1 μM and 1.5 for SK2 co-expressed with CaM(D_EF2,3,4A). (C) Current responses to voltage ramps from −100 mV to 70 mV in the presence of the indicated intracellular Ca²⁺ concentrations. Traces recorded in the presence of 1 μM Ca²⁺ are shown by dark lines. (D) Currents evoked by voltage steps in an inside-out patch expressing SK2 (left) or with CaM(D_EF2,3,4A) (right) in the presence of 10 μM Ca²⁺. Voltage steps were from −100 to 100 mV in 20 mV increments from a holding potential of 0 mV. The current and time calibrations are 10 nA and 20 ms, respectively. Adapted from ref.³¹ © [Nature]. Permission to reuse must be obtained from the rightsholder.