(464h) Ion Transport Near Biological Membranes I : The Role of Dielectric Mismatch

The partitioning and selective transport of ions across lipid membranes forms the basis of electrical signaling in biological cells. However, commonly employed “equivalent circuit” frameworks to understand these signaling processes ignore interfacial ionic gradients, the dielectric properties of the membrane, and the spatially localized nature of transmembrane ionic fluxes. To address these gaps, we present a model of ion pumping through a lipid membrane and study the resulting spatiotemporal ionic dynamics using the Poisson-Nernst-Planck framework. In this first of two talks, we begin by analyzing the spatially uniform pumping of ions across the membrane, resulting in a 1D model. With analytical and numerical solutions for electric potential and ionic concentrations in this 1D model, we show that one can recover the capacitor model for the membrane consistent with earlier works. We then consider the case of spatially localized ion pumping in 3D, resolving both in- and out-of-plane variations in diffuse charge and electric potential near the lipid membrane. Analyzing the short-time dynamics, we find that the transmembrane electric potential exhibits a dipolar (1/r³) scaling far from the pump, but a monopolar (1/r) scaling near the pump. We show the monopolar region, where the electric fields are stronger and decay more slowly, to be a consequence of the large mismatch in dielectric permittivity between the lipid membrane and the surrounding fluid. The subsequent talk analyzes the full spatiotemporal dynamics of charge reorganization and in-plane signal propagation.