The electrophysiology of pairs of cardiac atrial and pacemaker cells

The electrical activity of the atrial chambers of the heart is currently investigated by means of the most advanced techniques like electrocardiographic imaging and three-dimensional numerical modeling. Studies on the electrotonic interaction at the level of cell pairs have historically played an important role in cardiac research and have given a fundamental contribution to the knowledge on the field. Cell pairs dynamics, in fact, represent the simplest form of electrotonic interaction and allow to isolate the fundamental rules governing the source-sink relationship between the different cell types found in the atria. The electrophysiological investigation on cell pairs includes enzymatically isolated pairs of cells physically connected by gap junctional channels and simultaneously brought in patch clamp whole cell configuration. It also includes physically separated cells externally connected by an electronic circuit mimicking gap junctional coupling. In this latter case, pairs made of an atrial cell and a pacemaker cell, either isolated from the sinoatrial node (SAN) or from the atrioventricular node (AVN), can be studied as well. Pairs made of a real enzymatically isolated cell and a mathematical cell model can also be studied. Cell pairs interaction can also be modelled numerically. This review will discuss results obtained through all these approaches by focusing on the fundamental results achieved by their use. These include the measure of gap junctional resistance between atrial cells and between pacemaker cells, of its physiological and pharmacological modulation, and of the complex dynamics that regulates the source-sink relationship in atrial-atrial, atria-SAN, atrial-AVN, atrial-fibroblasts and SAN-fibroblasts pairs.