Ion permeation across model lipid membranes: A kinetic approach

Current-voltage characteristic measurements have been utilized to investigate the ion transport properties in dimyristoylphosphatidylethanolamine [DMPE] 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 the Skinner model, considering different kinetic reactions at the water-membrane interfaces and within the membrane core. Transient aqueous pores produced by thermal fluctuations facilitate the ion transport, avoiding the Born energy barrier associated with the solubility-diffusion mechanism. The pore-ion coupling, allowing ion translocation across the bilayer, is modeled as 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 stability against rupture of the bilayer, and the difference in the electrochemical potentials (mu(i) - mu(e)) associated with the two membrane interfaces 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 concentration and temperature, have been obtained. The relevance of these parameters in connection with the proposed model is briefly discussed.