Progress and Gaps in Understanding the Electrophysiological Properties of Morphologically Normal Cells From the Cardiac Atrioventricular Node

The atrioventricular node (AVN) is a small but critically important component of the cardiac electrical conduction system and is located at the junction between right atrium and right ventricle of the heart. It plays important roles in normal and abnormal impulse propagation. Mathematical models of the conduction properties of the AVN have been made, but detailed in silico reconstruction of AVN electrophysiology lags behind that of other cardiac regions. One important facet of detailed reconstruction of AVN electrical activity is the development of comprehensive, ionic conductance-based models of single cell electrophysiology. With a view to facilitating the construction of such models, this article reviews progress made regarding single AVN cell electrophysiological data during the last decade, predominantly focusing on that derived from morphologically normal AVN cells. Properties and potential roles of a range of currents are discussed: including L-type and T-type calcium currents (I Ca,L and I Ca,T respectively), background current, hyperpolarization-activated current (I f ), delayed and transient outward potassium currents (I Kr and I to , respectively), sodium–calcium exchanger current (I NaCa ), the sustained inward current (I st ) and acetylcholine-activated potassium current (I KACh ).