Mechanisms for nonuniform propagation along excitable cables

Area of Science:

• Computational neuroscience
• Biophysics
• Cardiac electrophysiology

Background:

• Action potential propagation is crucial for physiological function.
• Non-constant propagation velocity and disrupted temporal patterning can lead to pathological conditions like cardiac reentry.
• Understanding these phenomena requires detailed modeling of excitable media.

Purpose of the Study:

• To investigate mechanisms causing non-constant action potential propagation velocity.
• To explore factors contributing to the disruption of temporal patterning of action potentials.
• To analyze the role of cable inhomogeneities, ionic model properties, and previous activity on propagation dynamics.

Main Methods:

• Simulations using discrete excitable cells coupled by gap junctions.
• Analysis of ionic models, including the Hodgkin-Huxley model.
• Investigation of the dispersion relation, c(T), describing speed dependence on inter-spike interval.
• Development of a kinematic recipe for predicting timing changes.

Main Results:

• Cable inhomogeneities (geometric changes, altered coupling) can cause conduction delays, block, or reflection, relevant to cardiac reentry.
• Saddle point threshold behavior in ionic models significantly contributes to long conduction delays.
• Previous activity influences propagation speed, characterized by the dispersion relation c(T).
• Supernormal conduction is linked to excitability overshoots in the return to rest, observable in the dispersion relation.

Conclusions:

• Both physical cable properties and intrinsic ionic model dynamics play critical roles in action potential propagation irregularities.
• The identified mechanisms provide a framework for understanding and potentially predicting complex electrophysiological behaviors in cardiac tissue.
• Further research is needed to integrate these findings into cardiac models and elucidate the ionic basis of phenomena like supernormal conduction.