Slow inactivation occurs with the same time constant but with shifted voltage dependence in the heterotetramers compared with the 4wt tetramer. (A) Time course of slow inactivation during a 100-s pulse. Current traces, at the indicated voltages, from representative oocytes expressing 4wt (left), 2wt/2mut (middle), and 1wt/3mut (right). The weighted time constants represent an average from four to five experiments. The internal and external solutions contained 120 and 12 mM K⁺, respectively. (B) Voltage dependence of slow inactivation. The normalized peak tail current at +40 mV is plotted as a function of the HP and fitted to a Boltzmann distribution: G_m = G_min + G_max/(1 + exp[−z(V_1/2 −V_m)F/RT]). 4wt data are shown as filled squares, 2wt/2mut data are shown as filled circles, and 1wt/3mut data are shown as filled triangles. Cut-open voltage clamp measurements. The internal and external solutions both contained 120 mM K⁺.