Movie 1. P_low is 0. This movie illustrates a Monte Carlo simulation by using a selectivity filter with one K-binding site that is fixed in the high-affinity state, as indicated by the binding site being a red circle (P_low = 0). In this simulation and all of the following ones, the top compartment contains 25 K and 25 Na ions that move around with random velocities and directions to simulate diffusion. At 8 sec into the movie, the first K ion arrives at the entrance to the filter and it is captured by the binding site. For the remainder of the simulation, the K ion is trapped in the filter and all other ions that appear at the entrance are bounced back into solution. No ions are able to cross the filter and the permeation rate is 0.