Ion transport in lipid bilayer membranes through aqueous pores

In this note, we analyze ionic transport in lipid model bilayers across pre-existing transmembrane water pores that represent a facilitated pathway for the movement of single inorganic ions and offer the possibility to overcome the Born charging energy. Following the statistical rate approach recently proposed by Skinner et al., we present a kinetic model that involves the formation of a pore-ion complex at the membrane-solution interface and its diffusion through the membrane core. The overall process is described as due to four kinetic reactions consisting respectively in the ion-pore coupling and ion-pore uncoupling (treated as second-order reactions) and translocation of free- and ion-occupied pore through the membrane, treated as simple first-order reactions. The modified kinetic approach presented here may be regarded as a generallization of an our previous work where the pore diffusion, either in presence or in absence of an ion was treated with the same rate constants. This modification should allow a better description of the voltage-current relationships observed in lipid bilayer membranes under the influence of potential and ion concentration gradients, particularly as far as deviations from ohmic behaviour are concerned. (C) 1999 Elsevier Science B.V. All rights reserved.