Cardiac Purkinje cells (PCs) are morphologically and electrophysiologically different from ventricular myocytes and, importantly, exhibit distinct calcium (Ca(2+)) homeostasis. Recent studies suggest that PCs are more susceptible to action potential (AP) abnormalities than ventricular myocytes; however, the exact mechanisms are poorly understood. In this study, we utilized a detailed biophysical mathematical model of a murine PC to systematically examine the role of cytosolic Ca(2+) diffusion in shaping the AP in PCs. A biphasic spatiotemporal Ca(2+) diffusion process, as recorded experimentally, was implemented in the model. In this study, we investigated the role of cytosolic Ca(2+) dynamics on AP and ionic current properties by varying the effective Ca(2+) diffusion rate. It was observed that AP morphology, specifically the plateau, was affected due to changes in the intracellular Ca(2+) dynamics. Elevated Ca(2+) concentration in the sarcolemmal region activated inward sodium-Ca(2+) exchanger (NCX) current, resulting in a prolongation of the AP plateau at faster diffusion rates. Artificially clamping the NCX current to control values completely reversed the alterations in the AP plateau, thus confirming the role of NCX in modifying the AP morphology. Our results demonstrate that cytosolic Ca(2+) diffusion waves play a significant role in shaping APs of PCs and could provide mechanistic insights in the increased arrhythmogeneity of PCs.
Keywords: action potential; arrhythmias; calcium diffusion; cardiac Purkinje cell.