A Primitive Model for Predicting Membrane Currents in Excitable Cells Based Only on Ion Diffusion Coefficients

TL;DR

This paper introduces a simple model for predicting membrane currents in excitable cells using only ion diffusion coefficients, eliminating the need for empirical gating parameters, and successfully matches experimental data.

Contribution

It presents a novel primitive model that predicts ion currents solely based on diffusion coefficients, bypassing traditional gating parameter reliance.

Findings

Model accurately predicts current pulse times across channel densities.

Predictions align with data from giant squid axons.

Current pulse times vary with channel density as described by the model.

Abstract

Classical models for predicting current flow in excitable cells such as axons, originally proposed by Hodgkin and Huxley, rely on empirical voltage-gating parameters that quantify ion transport across sodium and potassium ion channels. We propose a primitive model for predicting these currents based entirely on well-established ion diffusion coefficients. Changes inside the excitable cell due to the opening of a central sodium channel are confined to a growing hemisphere with a radius that is governed by the sodium ion diffusion coefficient. The sodium channel, which is open throughout the calculation, activates and deactivates naturally due to coupled electrodiffusion processes. The characteristic time of current pulses, which are in the picoampere range, increases from 10$^{-5}$ to 10$^{-1}$ s as channel density is decreased from 10,000 to 1 channel per micrometer squared. Model predictions are compared with data obtained from giant squid axons without invoking any gating parameters.