Comparison of gating in 2 mM Ca²⁺_o vs. Ba²⁺_o. Values are from all control recordings (n = 52 in Ca²⁺_o, n = 47 in Ba²⁺_o). (A) Effects of Ca²⁺ (▪) and Ba²⁺ (○) on inactivation of inward currents. Time constants were averaged over a 20–30-mV range, centered ∼30 mV negative to the reversal potential (A). (B) I-V relations in 2 mM Ca²⁺_o vs. 2 mM Ba²⁺_o. The same symbols were used in B and D–F (defined in B). Outward currents for the most positive voltage steps (up to +100 mV) are offscale. (C) Voltage shifts, 2 mM Ba²⁺ minus 2 mM Ca²⁺. Experimental values (“Data”) and theoretical values (“Model”) are from the analysis shown in D–F. Voltage shifts were measured as in Fig. 5, for both experimental data and model output. (D) P_O,r in 2 mM Ca²⁺_o or Ba²⁺_o (from Fig. 2, C and D). (E) τ_IIV (from Fig. 3, A and B). (F) T_Peak (from Fig. 3, E and F). Smooth curves in D–F are calculated from a fit to the Serrano et al. (1999) model (see text). Parameter values for Ca²⁺ (named as in Serrano et al., 1999) were k_V = 2521.1 s⁻¹, k_-V = 7.7 s⁻¹, k_O = 3601.1 s⁻¹, k_-O = 23.1 s⁻¹, k_I = 70.1 s⁻¹, k_-I = 1.4 s⁻¹, f = 0.7555, h = 0.0999. k_V, k_-V, and k_-O changed with depolarization e-fold for 24.8062, −17.0591, and −34.114 mV (respectively). Parameters were identical in Ba²⁺, except k_I = 122.5 s⁻¹, thus k_I,Ca/ k_I,Ba = 0.57.