Na(+) current in human ventricle: implications for sodium loading and homeostasis.

The Na current (I(Na)) in human ventricle is carried through a specific isoform of the voltage gated Na channel in heart. The pore forming alpha-subunit is encoded by the gene SCN5A. Up to four beta-subunits may be associated, and the larger macromolecular complex may include attachments to cytoskeleton and scaffolding proteins, all of which may affect the gating kinetics of the current. I(Na) underlies initiation and propagation of action potentials in the heart and plays a prominent role in cardiac electrophysiology and arrhythmia. In addition, I(Na) also loads the ventricular cell with Na(+) ions and plays an important role in intracellular Na homeostasis. This review considers the structure and function of the human cardiac Na channel that carries I(Na) with a particular consideration of the implications of alterations in I(Na) in acquired cardiac diseases such as hypertrophy, failure, and ischemia, which affect Na loading.