Chord conductances from IIV relations. (A and B), Ca²⁺_o, (D and E) Ba²⁺_o. (C and F) Block by 0.01–0.5 mM Ca²⁺_o (C) or Ba²⁺_o (F), calculated from the conductance in the indicated concentration divided by the conductance in 100 nM Ca²⁺_o or Ba²⁺_o. Error bars (SEM) include errors in both numerator and divisor, from standard error propagation analysis. Note that these comparisons across datasets yield limiting ratios (at ∼+100 mV) not exactly equal to 1. Same symbols and color coding as Fig. 2.