Speaker
Description
In cardiac electrophysiology, ionic currents at the subcellular scale drive electrical activity at the tissue scale, making accurate cellular modeling essential for understanding cardiac function. Experimental inaccessibility of subcellular compartments in intact tissue positions mathematical models as essential tools for studying excitation propagation and motivates the development of multiscale frameworks. We present a biophysically derived computational model for action potential propagation in linear strands of cardiac myocytes that explicitly couples gap junction and ephaptic mechanisms. The model incorporates a biophysically detailed ionic model (Luo-Rudy dynamic) with intracellular concentration dynamics, coupled to a continuum PDE–DAE system governing transmembrane voltage and cleft ion concentrations. Cleft concentration dynamics, governed by conservation of mass, balance spatially localized transmembrane ionic currents at intercalated discs from adjacent myocytes with Goldman-Hodgkin-Katz electrodiffusive exchange to the bulk extracellular space. Equations are discretized using finite volume methods to preserve conservation and integrated using operator splitting with a multirate GARK method to resolve the multiple temporal scales. This framework enables mechanistic investigation of ephaptic coupling through dynamic ion concentrations in the extracellular cleft and demonstrates stable propagation with recovery of known conduction limits in ventricular tissue.
