Repolarizare

Repolarizare, or repolarization, is the process by which a cell’s membrane potential returns to its resting level after depolarization. It is a key phase of action potentials in excitable cells such as neurons and cardiomyocytes and is accomplished by specific ion channels and pumps that restore ionic gradients disrupted during depolarization.

In neurons, an action potential begins with depolarization as voltage-gated Na+ channels open. Soon after the peak, these Na+ channels inactivate while voltage-gated K+ channels open, allowing potassium to exit the cell. This outward K+ current drives the membrane potential back toward the resting level, producing repolarization. The membrane may briefly hyperpolarize below its resting potential before the Na+/K+ ATPase and other currents restore baseline conditions.

In cardiac muscle, repolarization corresponds mainly to phase 3 of the cardiac action potential. It is driven by outward potassium currents, including delayed rectifier currents (I_Kr and I_Ks) and inward rectifier I_K1, as calcium influx through L-type channels declines. Completion of repolarization returns the membrane to its resting potential and re-establishes cellular refractoriness. On the electrocardiogram, ventricular repolarization is represented by the T wave, while timing relationships with depolarization contribute to intervals such as the QT interval.

Clinical relevance: disturbances of repolarization can predispose to arrhythmias. Prolonged repolarization (long QT) increases the risk of torsades de pointes, while other abnormalities of repolarizing currents can lead to ischemia- or drug- or genetic-related arrhythmias. The concept of repolarization reserve describes the heart’s capacity to cope with impaired repolarizing pathways.