Two-site versus continuum diffusion model of blocker dynamics in a membrane channel: Comparative analysis of escape kinetics

This paper deals with the escape of a charged blocker molecule from a voltage-biased membrane channel with a constriction zone which the molecule cannot pass through. Recently, we developed a two-site model of the blocker dynamics in such a system and applied it to analyze the escape kinetics. Here, we compare the decay of the blocker survival probability predicted by the two-site model with that for the survival probability given by a more accurate model which assumes continuum diffusion of the blocker molecule inside the channel. The main finding of the present work is that both models predict the same decay of the survival probability at long times. This result is of practical importance since only the long-time tail of the survival probability can be studied in single-channel experiments in which, due to a limited time resolution, only long-lasting individual events of channel blockades can be measured.