Theories of Ion Permeation

The Perspectives on Ion Permeation in the June issue of The Journal of General Physiology provided a unique exposition of contrasting views regarding kinetic rate models, electrodiffusions, Brownian dynamics, and PoissonNernst-Planck (PNP). The debate is timely, healthy, and desirable, because recent progress in the determination of the three-dimensional structure of biological ion channels at atomic resolution gives a fresh impetus to efforts directed at understanding the fundamental principles governing ion permeation (Cowan et al., 1992; Chang et al., 1998; Doyle et al., 1998). Theory is expected to play an important role in those efforts, though we are hard pressed to develop a consensus toward specific approaches. A necessary prerequisite for making any global judgement, however, is to understand the significance of the various treatments and how they relate to one another. In my view, there remains significant confusion about these issues that I hope the present contribution will help clarify.