Transient outward potassium channel: a heart failure mediator

Transient outward K(+) current (Ito) plays a crucial role in shaping the early phase of repolarization and setting the plateau voltage level of action potential. As a result, it extensively affects membrane current flow in the plateau window. A great body of evidence illustrates a transmural gradient of I to within ventricular wall with much higher density in epicardial than endocardial myocytes, which is important for the physiological ventricular repolarization. In heart failure (HF), this gradient is diminished due to a greater reduction of I to in epicardial myocytes. This attenuates the transmural gradient of early repolarization, facilitating conduction of abnormal impulses originated in the epicardium. In addition, I to reduction prolongs action potential duration and increases intercellular Ca(2+), thus affecting Ca(2+) handling and the excitation-contraction coupling. Furthermore, increased intercellular Ca(2+) could activate CaMKII and calcineurin whose role in cardiac hypertrophy and HF development has been well established. Based on the impact of I to reduction on electrical activity, signal conduction, calcium handling and cardiac function, restoration of I to is likely a potential therapeutic strategy for HF. In this review, we summarize the physiological and pathological role of cardiac I to channel and the potential impact of I to restoration on HF therapy with an emphasis of recent novel findings.