Atypical mechanism of conduction in potassium channels

Potassium channels can conduct passively K⁺ ions with rates of up to [almost equal 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⁺.