Physics of the Propagating Action Potential

TL;DR

This paper develops a new phase space cable equation for action potentials, confirming experimental data, and introduces a novel ionic channel model incorporating quantum tunnelling and phase transitions, with implications for memory mechanisms.

Contribution

It presents a charge conserving phase space cable equation and a modified Avrami model for ion channel kinetics, integrating quantum effects and predicting phase transitions in sodium channels.

Findings

Ionic current crossing zero twice as a function of propagation constant.

Outward sodium current during recovery phase from axoplasmic effects.

Predicted phase transitions in sodium channels suggest mechanisms for memory encoding.

Abstract

We derive a charge conserving phase space cable equation for the propagating action potential, expressing ionic, capacitive and axoplasmic currents as functions of membrane potential. The new equation prediction of ionic current crossing the zero current axis twice as function of the propagation constant is confirmed by the Rosenthal-Bezanilla experimental data. Analysis of the ionic current during the recovery phase reveals an outward sodium current, unobserved in voltage clamp experiments, arising from the axoplasmic modulated Ohmic current creating a positive charge gradient opposing the sodium concentration gradient. Using a single assumption, that the fraction of open channels follows a time-dependent modified Avrami (mAvrami) equation that incorporates the ionic time rate yielding the fine structure constant as a dimensionless scaling factor, we fit experimental ionic currents across different ions and temperatures. The fitting results predict already established observations, including the delayed onset of sodium inactivation, the magnitude of gating charges, and the fact that the fraction of open sodium channels is about one fifth when most of the gating charges have moved. These alignments with already established facts logically increase the confidence that the remaining predictions/hypothesis will be confirmed by future experiments. The mAvrami kinetics predictions include a universal role for the fine-structure constant in ion traversing ionic channels, and temperature independent ionic activation energies are suggestive of quantum tunnelling. Further predictions reveal continuous phase transitions in sodium channels at both initiation and peak of the action potential implying symmetry changes in sodium channel states and pointing to a potential mechanism for memory encoding and storage. The calculated optimal sodium channel density matches observed values.