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Cardiac transient outward potassium current

Ion current

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Through Potassium

The Ito1 is generated by voltage-gated K+ channels Kv1.4, Kv4.2, and (especially) 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.
  • Ito1 density is significantly lower in the cells of a failing heart in comparison to the cells of a healthy heart.
  • There is correlation between decreased Ito1 density and atrial fibrillation.
  • Ito activation is inhibited by thyrotropin (TSH). This mechanisms may be one of the reasons for the observation that both bradycardia and atrial fibrillation are common in hypothyroidism.
  • An increase in the Ito1 density caused by a mutation in Kv4.3 can be a cause of Brugada Syndrome.

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