A Cardiomyocyte Model Integrating Electrophysiology and Mechanics Based on Triphasic Theory

Abstract

Although many numerical simulations have been proposed to determine the mechanisms of cardiac excitation-contraction coupling, neither potential distribution nor mobility of the cytosol and ions has been taken into consideration in these models. Therefore, we applied the triphasic theory to our previously reported 3D finite element model of cardiomyocytes to examine the significance of these factors in cardiac physiology. The salient feature of triphasic theory allowed us to study the behavior of solids (proteins), fluids (cytosol) and ions governed by mechanics and electrochemistry in an integrative manner in detailed subcellular structures, including myofibrils, mitochondria, the sarcoplasmic reticulum, membranes and t-tubules. Simulation results showed that there was a 0.5 mV electrical potential difference inside t-tubules at the onset of depolarization, and that this potential distribution was inverted when Na⁺ channel density was altered. We also found a significant movement of the cytosol from the A-zone to the I-zone of myofibrils and ejection of fluid from t-tubules to the extracellular compartment during contraction. Our results indicated the capability and necessity of triphasic theory in the detailed analysis of cardiac physiology.