To return to a polarized condition
The term repolarize refers to the returning to an initially polarized condition. In physiology, the plasma membrane of a cell (e.g. nerve cell) can be repolarized; that is from being polarized to depolarized, and then back to being polarized again. At rest, the plasma membrane has a negative membrane potential. But with the process of depolarization, the membrane shifts to a positive membrane potential. However, this occurs rather abruptly and briefly. The membrane returns to a polarized state and the process is called repolarization. This is possible through physiological mechanisms involving the efflux and influx of ions across the plasma membrane. The movement of ions into and outside of the cell is regulated by transport proteins located in the plasma membrane.
In repolarization, the negative membrane potential of the cell is restored through the regulation of the movement of ions via the K+ channels. Examples of K+ channels are A-type channels, delayed rectifiers, and Ca2+-activated K+ channels.1 When there is an efflux of K+ ions from the cell via the K+ channels in the plasma membrane, the electrical charge of the internal environment of the cell is able to return to negative.
Word origin: re- (again) + polarize
1 Purves D, Augustine GJ, Fitzpatrick D, et al., ed. (2001). Neuroscience (2. ed.). Sunderland, Mass: Sinauer Assoc.