The AMFE data are reproduced by the four-site model. All four panels show experimental Ba²⁺/Ca²⁺ MF data at different tail voltages (symbols). Total divalent cation concentration (Ba²⁺ + Ca²⁺) = 30 mM is in A and B and 3 mM is in C and D. (A and C) Simulations (smooth lines) using the three-site model (insets). The well electrical distances were 0.35, 0.5, and 0.65. For Ba²⁺ and Ca²⁺, respectively, the three wells were −2.65, −12.75, and −2.65 and −4.6, −15, and −4.6 kT deep and the four barriers were 8.6, −0.7, −0.7, and 9.6 and 8.6, −1, −1, and 9.6 kT high. (B and D) The same data were fit with the four-site model with well positions at 0.1, 0.2, 0.5, and 0.9. For Ba²⁺ and Ca²⁺, respectively, the four wells were −3.5, −1, −12.3, and −2.5 and −3.5, −4.6, −14.7, and −4.6 kT deep, while the five barriers were 8.6, −0.7, −0.7, −0.7, and 9.6 and 8.6, −1, −1, −1, and 9.6 kT high. The relative Ca²⁺ and Ba²⁺ levels are illustrated below C and D.