Ion permeation across model lipid membranes: A kinetic approach

Current-voltage characteristic measurements have been utilized to investiga te the ion transport properties in dimyristoylphosphatidylethanolamine [DMP E] bilayers at the tip of a patch pipet (patch-clamped pure lipid bilayers) with the aim of determining the permeation of Ca++ and Rg(++) ions in the presence of KCl aqueous solutions. at two different ionic strengths (1 and 10 mM). The data have been analyzed on the basis of a modified version of t he Skinner model, considering different kinetic reactions at the water-memb rane interfaces and within the membrane core. Transient aqueous pores produ ced by thermal fluctuations facilitate the ion transport, avoiding the Born energy barrier associated with the solubility-diffusion mechanism. The por e-ion coupling, allowing ion translocation across the bilayer, is modeled a s a kinetic process within the statistical rate theory. Using this approach , from the I-V characteristics measured at different temperatures below the lipid transition temperature, the surface energy Gamma, that governs the s tability against rupture of the bilayer, and the difference in the electroc hemical potentials (mu(i) - mu(e)) associated with the two membrane interfa ces at the inner and external medium, have been determined. Values of Gamma in the range from 0.010 to 0.030 J/m(2), depending on the salt concentrati on and temperature, have been obtained. The relevance of these parameters i n connection with the proposed model is briefly discussed.