Modeling ion transport in tethered bilayer lipid membranes. 1. Passive ion permeation.

Ion transport across tethered bilayer lipid membranes (tBLMs) is modeled using a hybrid network description which combines potential-dependent rate equations with passive electrical elements. Passive permeation of ions is described by the integrated Nernst-Planck equation. Simulations based on this model are performed with the network simulation program SPICE (simulation program with integrated circuit emphasis). Electrochemical impedance spectra of tBLMs are simulated with this algorithm and challenged by spectra measured with tBLMs submersed in 0.1 M KCl solution and subjected to various potential differences. It is found that the simulated spectra can only satisfactorily represent the experimental data if the permeability coefficients of the ions are dependent on the membrane potential. It is concluded that the mechanism of passive ion transport across the tBLM seems to follow the transient pore model rather than the solubility-diffusion model. This algorithm can be easily extended to include ion transport processes due to channels, carriers, or pumps incorporated into the tBLM.