Single-channel I-V curves recorded in the cell-attached configuration from the mouse muscle AChR containing the εT264P mutation, one of the constructs studied in Elenes et al. (2009). Note the different current axis scales of the two panels. (A) I-V relationships in the presence of saturating concentrations of the indicated cations (as their chloride salts) in the pipette solution. In the case of Ca²⁺, the slopes estimated with 100 or 200 mM Ca²⁺ were indistinguishable, and hence, the corresponding data points were pooled together. (B) I-V relationships in the presence of the indicated binary mixtures of cations in the pipette solution. In the case of Na⁺, 100 mM Ca²⁺ was enough to bring the single-channel conductance to a value close to that estimated in the presence of Ca²⁺ alone; however, in the cases of K⁺ and Cs⁺, 200 mM Ca²⁺ was needed. The pipette solutions also contained 10 mM HEPES, and the final pH was 7.4. To facilitate the visual comparison of slopes, all I-V curves were shifted along the voltage axis so that their linear projections go through the origin.