Effects of Ni²⁺ on currents carried by Na⁺. (A) IIV relations, (B) chord conductances, and (C) inhibition by Ni²⁺, as conductance ratios (Ni²⁺/control). (D) Effects of Ni²⁺ on IIV tail currents carried by Na⁺, from single exponential fits. (E) Pseudo first-order rate constants for Ni²⁺ block, calculated from single exponential fits. (F) I-V relations, (G) I-V relations on an expanded scale, (H) chord conductances, and (I) inhibition by Ni²⁺, as conductance ratios (Ni²⁺/control). The smooth curves in I are the best fit to a Woodhull (1973) model. Symbols and color coding in A apply to all panels in this figure. n = 6 (10 μM Ni²⁺) or n = 4 (30 μM Ni²⁺ and 100 μM Ni²⁺), except n = 5 in 10 μM Ni²⁺ and n = 3 in 30 μM Ni²⁺ for D and E.