The Role of Time Variant Resistance and Electromotive Force in Ionic Systems Related to Cell Membranes: The Excitability Properties of Frog Skin and Toad Bladder
type: CreativeWork
description: Central to the modern theory of the electrical properties of cells is the permeability of the plasma membrane to the ions passing across this structure; it has been our purpose to explore, both theoretically and experimentally, the physical implications of this point-of-view. The cornerstone of our analysis has been the fundamental flux equations of Nernst and Planck, which describe the movement of ions in solution subject to gradients of electrochemical potential. As a direct consequence of these equations, we have seen that the potential difference between two points in a solution is the sum of two terms: an intrinsic electromotive force (emf.) associated with the gradients of ionic concentrations, and an ohmic potential difference (IR drop) arising when current flows through the system. In order to illustrate the meaning and significance of these two terms, we have considered the voltage-current relationships in certain synthetic membrane systems; namely, the homogeneous uncharged membrane, the homogeneous fixed-charge membrane, and the two-layer a "sandwich" membrane consisting of a positive and negative fixed-charge lattice in series. Our analysis of these systems enabled us to bring up for discussion the important concepts of non-linear voltage characteristics, slope and chord resistance, time-variant resistance and emf., and rectification. We have noted that in the sandwich membrane of high fixed charge density, the membrane "resistance" is primarily the result of emf.'s generated in the face of current flow, and we have demonstrated the behavior of such membranes experimentally. We then turned our attention to a more direct consideration of the ionic theory of electrical events in cells, and in particular we focused upon the equivalent circuit used to describe the electrical characteristics of the plasma membrane. In order to determine what such an equivalent circuit representation can mean physically, we returned to the basic flux equations and have conside…
abstract: Central to the modern theory of the electrical properties of cells is the permeability of the plasma membrane to the ions passing across this structure; it has been our purpose to explore, both theoretically and experimentally, the physical implications of this point-of-view. The cornerstone of our analysis has been the fundamental flux equations of Nernst and Planck, which describe the movement of ions in solution subject to gradients of electrochemical potential. As a direct consequence of these equations, we have seen that the potential difference between two points in a solution is the sum of two terms: an intrinsic electromotive force (emf.) associated with the gradients of ionic concentrations, and an ohmic potential difference (IR drop) arising when current flows through the system. In order to illustrate the meaning and significance of these two terms, we have considered the voltage-current relationships in certain synthetic membrane systems; namely, the homogeneous uncharged membrane, the homogeneous fixed-charge membrane, and the two-layer a "sandwich" membrane consisting of a positive and negative fixed-charge lattice in series. Our analysis of these systems enabled us to bring up for discussion the important concepts of non-linear voltage characteristics, slope and chord resistance, time-variant resistance and emf., and rectification. We have noted that in the sandwich membrane of high fixed charge density, the membrane "resistance" is primarily the result of emf.'s generated in the face of current flow, and we have demonstrated the behavior of such membranes experimentally. We then turned our attention to a more direct consideration of the ionic theory of electrical events in cells, and in particular we focused upon the equivalent circuit used to describe the electrical characteristics of the plasma membrane. In order to determine what such an equivalent circuit representation can mean physically, we returned to the basic flux equations and have conside…
author: Finkelstein, Alan
keywords: plasma membrane, ion permeability, Nernst-Planck equations, equivalent circuit, time-variant resistance, action potential, Life Sciences
date published: 1963-01-01T08:00:00Z
date modified: 2026-07-24T04:10:53Z
provider: Rockefeller
publisher: Networked Digital Library of Theses and Dissertations
type: WebPage
source organization: Rockefeller