The authors of this interesting paper report in Fig. 7 values of the reversal potential of VDAC32 as a function of ionic strength keeping the ratio of the salt concentrations constant. They include the predictions from GHK theory and Nernst/Plank theory, which, of course, show no change in reversal potential with ionic strength. If they had chosen to use the Large Channel Theory (1) they would have obtained a remarkably good fit. Since figures cannot be inserted into comments, the comment with the figure can be obtained from the following link: https://dl.dropbox.com/u/...
The experimental data in the figure was taken from Fig. 7 using a ruler. The Large Channel Theory does not require knowledge of the detailed structure of the channel. Indeed it has only one adjustable parameter: the charge density on the inner surface of the channel.
One might think that knowing the 3D structure of VDAC would result in a better agreement between theory and experiment. The problem is that the published 3D structures of VDAC are not of the native, functional structure (2). Regardless of this controversial aspect, the fact that the Large Channel Theory fits the data extremely well means that it embodies the essential features that determine how the reversal potential varies with ionic strength. The use of GHK theory and Nernst/Plank theory to understand the reversal potential of large channels should be discontinued as these fail miserably.


1. Zambrowicz, E.B. and Colombini, M. 1993. Zero-current potentials in a large membrane channel: a simple theory accounts for complex behavior. Biophysical Journal, 65: 1093-1100.
2. Colombini, M. 2009. The Published 3-D structure of the VDAC channel: native or not? Trends in Biochemical Sciences 34:382-389.