FIGURE 7.

Mutants F1144G, F1144K, and FY/GK reduce single-channel Ba²⁺ currents but have little effect on single-channel Ca²⁺ currents. (A) Example traces, showing currents through single wild-type or mutant channels, with either 110 mM Ca²⁺ (left) or 110 mM Ba²⁺ (right) as the charge carrier. Currents were evoked by depolarizations to −10 mV. The dashed lines in the left-hand set of traces show the amplitudes of Ba²⁺ currents in the corresponding channel type, for comparison. (B) Mean current-voltage relationships for single wild-type channels, with Ca²⁺ (○) or Ba²⁺ (•). The straight lines are linear fits of the data points, with conductance values of 19.0 pS for Ba²⁺ and 7.1 pS for Ca²⁺. (C) Summary of single-channel conductance values for Ba²⁺ (solid bars) versus Ca²⁺ (open bars). Conductance values were determined from the following numbers of patches: wild-type, Ca²⁺, n = 4, Ba²⁺, n = 3; F1144G, Ca²⁺, 5, Ba²⁺, 4; Y1152K, Ca²⁺, 3, Ba²⁺, 4; FY/GK, Ca²⁺, 3, Ba²⁺, 3; F1144K, Ca²⁺, 4, Ba²⁺, 3.