Multi-ion Na⁺ conduction/occupancy bands in the model calcium/sodium channel, showing occupancy shifts with ionic concentration. (A) Weak multi-ion sodium conduction bands M_n as established by Brownian dynamics simulations. (B) The corresponding occupancy P_c is an almost-washed-out Coulomb staircase whose steps shift slightly as the extracellular sodium concentration [Na] changes. The vertical dashed lines show the nominal positions of the LESWAS channel and its LEDWAS mutant.