Ion trajectories for simulations with K ⁺ /Rb ⁺ and pure Rb ⁺ . (A–D) Mixed cationic KCl/RbCl simulations with Rb⁺ preplaced in p23 and K⁺ in p34 were conducted at (A) −700 mV and (B and C) −500 mV. A simulation with a mixed cationic solution at −500 mV and preplacement of Rb⁺ in p23 and S3 is shown in D. (E–G) Simulations conducted for RbCl, with initial Rb⁺ placement in p23 and p34 at −250 mV are shown in the second row.