Atypical mechanism of conduction in potassium channels
Potassium channels can conduct passively K+ ions with rates of up to ≈108 ions per second at physiological conditions, and they are selective to these species by a factor of 104 over Na+ ions. Ion conduction has been proposed to involve transitions between 2 main states, with 2 or 3 K+ ions occupying the selectivity filter separated by an intervening water molecule. The largest free energy barrier of such a process was reported to be of the order of 2–3 kcal mol−1. Here, we present an alternative mechanism for conduction of K+ in potassium channels where site vacancies are involved, and we propose that coexistence of several ion permeation mechanisms is energetically possible. Conduction can be described as a more anarchic phenomenon than previously characterized by the concerted translocations of K+–water–K+.