A MOLECULAR THEORY FOR NONOHMICITY OF THE ION LEAK ACROSS THE LIPID-BILAYER MEMBRANE

The current-voltage relationship of ion leak (i.e., ion transport invo lving neither special channels nor carriers) across the lipid-bilayer membrane has been observed to be log-linear above the ohmic regime. Th e coefficient of the linear term has been found to be universal for me mbranes and penetrants examined. This universality has been explained in terms of diffusion in an external field, where the ion position is described as a Markovian process. Such a diffusion picture can be ques tioned, however. It is also probable that a leaking ion gets over the potential barrier before experiencing sufficient random collision in t he membrane, considering that each ion is surrounded with long lipid m olecules aligned almost unidirectionally. As an alternative, we discus s this ion leak in terms of velocity distribution of the ions entering the membrane and density fluctuation of the lipids. We conclude that we can explain the universality without resorting to the diffusion pic ture.