Fig. 3. F1126E conducts Ba²⁺ ions as if they were Ca²⁺.

Whole-cell conductance is a product of the single channel current amplitude, the open probability (P_o) and the number of active channels. Peak tail-currents were measured from −80 to +20 mV following 50 msec depolarizing steps to +50 mV which were used to maximally activate wild-type (A) and F1126E (B) in 10 mM Ba²⁺ and Ca²⁺ from the same cell, thus minimizing differences in P_o that could arise from shifts in the voltage-dependence of activation. Linear portions of the current-voltage relationships (−50 to 0 mV) were normalized to amplitudes measured at 0 mV for wild-type (C) and F1126E (D). Normalized data were fit with the equation I_tail = G × (V − E_rev), where I_tail is the peak tail current, E_rev the reversal potential and G the maximal slope conductance. (E) Normalized slope conductances are plotted for wild-type (n = 8) and F1126E (n = 5).