The electrophysiology of ventricular cell pairs

Modern cardiac electrophysiology is largely focused on global electrical properties of tissue, frequently assessed by extracellular electrical recordings or optical mapping, whereas studies on the microscopic nature of action potential conduction are more rare, though fundamental to understand the whole-heart behavior. The electrophysiological dynamics of two ventricular myocytes electrically connected via gap junctions is the simplest conceivable model to study the laws governing the conduction of the electrical impulse within the heart ventricles. Since the enzymatic dispersion of cardiac cells has made it possible to isolate and investigate cardiac cell pairs directly, additional techniques have been introduced to investigate the problem, including coupling clamp, dynamic clamp, and numerical simulations. The physiology of a ventricular cell pair allows to define the basic laws governing the electrotonic interaction between cardiac cells in the absence of factors, like fiber orientation, heterogeneous spatial dispersion of electrophysiological properties, complex interaction with vessels and fibrotic tissue, that play a significant role in multicellular tissue studies. However, these laws remain at the base of our understanding of cardiac electrical functioning and should be bear in mind when dealing with the complexity of the whole organ level. This review will face both the technical issues encountered with the studies of ventricular cell pairs as well as the results found by the different authors concerning the physiological electrical coupling between cells, their physiological and pharmacological modulation, and the complex interactions between the conducted action potentials in the two cells.