IONIC TRANSPORT IN LIPID BILAYER-MEMBRANES

The current-voltage relationships of model bilayer membranes have been measured in various phospholipid systems, under the influence of both a gradient of potential and an ionic concentration, in order to descr ibe the ion translocation through hydrated transient defects (water ch annels) across the bilayer formed because of lipid structure fluctuati ons and induced by temperature. The results have been analyzed in the light of a statistical rate theory for the transport process across a lipid bilayer, recently proposed by Skinner et al. (1993). In order to take into account the observed I-V curves and in particular the devia tion from an ohmic behavior observed at high potential values, the ori ginal model has been modified, and a new version has been proposed by introducing an additional kinetic process. In this way, a very good ag reement with the experimental values has been obtained for all of the systems we have investigated (dimyristoylphosphatidyl ethanolamine bil ayers and mixed systems composed by dimyristoylphosphatidyl ethanolami ne/dimyristoylphosphatidylcholine mixtures and dimyristoylphosphatidyl ethanolamine/phosphatidic acid dipalmitoyl mixtures). The rate consta nts governing the reactions at the bilayer interfaces have been evalua ted for K+ and Cl- ions, as a function of temperature, from 5 to 35 de grees C and bulk ionic concentrations from 0.02 to 0.2 M. Finally, a c omparison between the original model of Skinner and the modified versi on is presented, and the advantages of this new formulation are briefl y discussed.