I would like to address two key issues related to the Perspectives on Ion Permeation. The first is the estimate of the size of the physical forces relevant for ion transport. Any good physical model of ion permeation requires the identification of the dominant forces. The second subject concerns a careful definition of the terms “mean field” and “mean field approximation.” Several articles in the field of ion permeation show considerable confusion about the mean field concept.
What is the relative size of the forces that ions experience while passing through a channel? To enter the channel ions have to become partly, if not completely dehydrated. Highly polar and even charged functional groups forming the channel walls compensate for this loss of hydration energy. In addition, there are two kinds of strong ion–ion forces: long range electrostatic forces...
