Cardiac transient outward potassium current
The cardiac transient outward potassium current is one of the ion currents across the cell membrane of heart muscle cells. It is responsible for the repolarizing phase 1 of the cardiac action potential. The Ito is produced by movement of positively charged potassium (K+) ions from the intracellular into the extracellular space. It exhibits rapid activation and inactivation. Ito1 is complemented with Ito2 resulting from Cl− ions to form the transient outward current Ito.
The Ito1 is generated by voltage-gated K+ channels Potassium [voltage-gated channel subfamily A member 4|Kv1.4], Kv4.2, and Kv4.3; these channels undergo ball-and-chain inactivation to terminate the current.
It occurs in atrial, ventricular, and conduction system cells. In ventricular myocardium, it is more potent in the epicardium than the endocardium; this transmural Ito1 gradient underlies the J wave ECG finding.
Role in disease
- Reduction in Ito1 density is associated with prolonged action potentials and is a common finding in cardiac disease.
- An increase in the Ito1 density caused by a mutation in Kv4.3 can be a cause of Brugada Syndrome.