Investigation of action potential propagation in a syncytium

Certain excitable cells, such as those in cardiac and smooth muscle, are known to form electrical syncytia. Cells within a syncytium are coupled to adjacent cells by means of structures known as gap junctions, which provide electrical continuity between cells. This results in the spread and propagation of electrical activity, such as action potentials (APs), from the originating cell to other cells in its syncytium. We propose that this ability of APs to propagate through an electrical syncytium depends on various syncytial features, and also the AP profile. The current study attempts to investigate these various factors using a computational approach. Simulations were conducted on a model of a three-dimensional syncytium using the NEURON simulation platform. The results confirm that the capacity of action potentials to propagate in a syncytium is influenced by the features of the action potential, and also the arrangement of cells within the syncytium. The excitability of biophysically identical cells was found to differ based on the size of the syncytium, their location within it, and the extent of gap junctional coupling between neighboring cells. Only a window of gap junctional coupling levels allowed both the initiation and propagation of action potentials. The results clearly exhibit the role of AP diversity and syncytial features in determining the spread of action potentials. This has significant implications for understanding the functioning of syncytial tissues, such as the detrusor smooth muscle, both in physiology and in disease.