Ion traces depicting the movement of Li ⁺ , Na ⁺ , and K ⁺ (green, light, and dark blue, respectively) along the main channel axis from simulations with Li ⁺ at varying initial positions, voltages, and ion compositions. (A and B) −500 mV with Li⁺/K⁺ and preplacement of Li⁺ in p34 with B as snapshot of a trajectory with Li⁺ residing in binding site Sb. (C) −500 mV with Li⁺/Na⁺ and Li⁺ preplaced in p23. The rapid diffusion of Li⁺ into the vestibule is depicted in the inset with higher temporal resolution. (D) −700 mV with Li⁺/Na⁺/K⁺ and Na⁺ preplaced in p34.