Cardiac transient outward potassium current

The cardiac transient outward potassium current (Ito1) is the main contributing current to the repolarizing phase 1 of the cardiac action potential, and results from movement of potassium (K+) ions from the intracellular to the extracellular space. It is complemented with Ito2 resulting from Cl - ions.

Mechanism
Ito1 is Ca2+-independent and has been clearly demonstrated in myocytes from different cardiac regions and species. There are two kinetic variants of cardiac Ito1: fast Ito1, called Ito1,f, and slow Ito, called Ito1,s. Recent findings suggest that Ito1,f is formed by assembly of Kv4.2 (KCND2) and/or Kv4.3 (KCND3) subunits, while Ito1,s is composed of Kv1.4 (KCNA4) and possibly Kv1.7 (KCNA7) subunits. In addition, several regulatory subunits and pathways modulating the level and biophysical properties of cardiac Ito have been identified.

Role in disease
A common finding in cardiac disease is reduction in Ito1 density with a loss of heterogeneity of Ito expression and associated action potential prolongation.