Anomalous reactances in electrodiffusion systems.

A frequency response analysis of a constrained diffusion boundary has been made by linearizing the Nernst-Planck equations for a small applied AC current. The number of time constants and their dependence on ionic concentrations and electric field as well as membrane parameters such as dielectric constant, thickness, etc. have been evaluated by this method. Numerical solutions have been carried out for cases when the Planck charging time can be neglected and the results are presented in the form of impedance loci. These impedance loci show that if the membrane separates two univalent electrolytes with a common anion it will exhibit a combined capacitative inductive response with a 90 degrees phase angle. The dependence of these anomalous reactances on ionic concentrations and the electric field is consistent with the behavior of the Hodgkin-Huxley axon suggesting that a homogeneous electrodiffusion regime could be adequate as a basic model for the kinetic behavior of biological membranes.