Specificities of atrial electrophysiology: Clues to a better understanding of cardiac function and the mechanisms of arrhythmias

The electrical properties of the atria and ventricles differ in several aspects reflecting the distinct role of the atria in cardiac physiology. The study of atrial electrophysiology had greatly contributed to the understanding of the mechanisms of atrial fibrillation (AF). Only the atrial L-type calcium current is regulated by serotonine or, under basal condition, by phosphodiesterases. These distinct regulations can contribute to ICa down-regulation observed during AF, which is an important determinant of action potential refractory period shortening. The voltage-gated potassium current, IKur, has a prominent role in the repolarization of the atrial but not ventricular AP. In many species, this current is based on the functional expression of KV1.5 channels, which might represent a specific therapeutic target for AF. Mechanisms regulating the trafficking of KV1.5 channels to the plasma membrane are being actively investigated. The resting potential of atrial myocytes is maintained by various inward rectifier currents which differ with ventricle currents by a reduced density of IK1, the presence of a constitutively active IKACh and distinct regulation of IKATP. Stretch-sensitive or mechanosensitive ion channels are particularly active in atrial myocytes and are involved in the secretion of the natriuretic peptide. Integration of knowledge on electrical properties of atrial myocytes in comprehensive schemas is now necessary for a better understanding of the physiology of atria and the mechanisms of AF.