In biology, depolarization is a positive-going change in a cell's membrane potential, making it more positive, or less negative. In neurons and some other cells, a large enough depolarization may result in an action potential. Hyperpolarization is the opposite of depolarization, and inhibits the rise of an action potential.
If, for example, a cell has a resting potential of –70mV, once the membrane potential changes to –50mV, then the cell has been depolarized. Depolarization is often caused by influx of cations, e.g. Na+ through Na+ channels, or Ca2+ through Ca2+ channels. On the other hand, efflux of K+ through K+ channels inhibits depolarization, as does influx of Cl– (an anion) through Cl– channels. If a cell has K+ or Cl– currents at rest, then inhibition of those currents will also result in a depolarization.
Because depolarization is a change in membrane voltage, electrophysiologists measure it using current clamp techniques. In voltage clamp, the membrane currents giving rise to depolarization are either an increase in inward current, or a decrease in outward current.
There are drugs, called depolarization blocking agents, that cause prolonged depolarization by opening channels responsible for depolarization and not allowing them to close, preventing repolarization. Examples include the nicotinic agonists suxamethonium and decamethonium.
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