Mg²⁺ slows gating charge movement in I287D+F324D channels, but not in control (W434F) or I287D channels. Gating currents were recorded from (A) I287D+F324D, (B) W434F, or (C) I287D channels in the absence or presence of Mg²⁺ using the pulse protocols described in the Fig. 8 legend. (Left) Representative ON gating current traces obtained at −9 mV in the absence (solid trace) or presence (dashed trace) of Mg²⁺ have been scaled and overlaid. (Right) Gating current traces recorded in the absence (■) or presence (○) of Mg²⁺ were fitted with a single-exponential component to obtain values for τ_on, which have been plotted versus voltage. In A, values of τ_on measured in the presence andabsence of Mg²⁺ differed significantly from −21 to +18 mV; P < 0.05 by ANOVA. Values of τ_on obtained at −9 mV are shown in Table II.