The cardiac transient outward potassium current (referred to as I
to1 or I
to) is one of the
ion currents across the cell membrane of
heart muscle cells. It is responsible for the (brief)
repolarizing phase 1 of the cardiac action potential (which suceeds depolarisation, and precedes the plateau phase). The I
to is produced by movement of positively charged
potassium (K+) ions from the
intracellular
This glossary of biology terms is a list of definitions of fundamental terms and concepts used in biology, the study of life and of living organisms. It is intended as introductory material for novices; for more specific and technical definitions ...
into the
extracellular space. It exhibits rapid activation and inactivation.
I
to1 is complemented with I
to2 resulting from Cl
− ions to form the transient outward current I
to.
The I
to1 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 I
to1 gradient underlies the
J wave ECG finding.
Role in disease
*Reduction in I
to1 density is associated with prolonged action potentials and is a common finding in
cardiac disease.
:*I
to1 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 I
to1 density and
atrial fibrillation
Atrial fibrillation (AF, AFib or A-fib) is an Heart arrhythmia, abnormal heart rhythm (arrhythmia) characterized by fibrillation, rapid and irregular beating of the Atrium (heart), atrial chambers of the heart. It often begins as short periods ...
.
:*I
to 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 I
to1 density caused by a mutation in Kv4.3 can be a cause of
Brugada Syndrome.
References
{{reflist, 30em
Electrophysiology
Cardiac electrophysiology