Depolarization
Overview
 
In biology, depolarization is a change in a cell's membrane potential
Membrane potential
Membrane potential is the difference in electrical potential between the interior and exterior of a biological cell. All animal cells are surrounded by a plasma membrane composed of a lipid bilayer with a variety of types of proteins embedded in it...

, making it more positive, or less negative. In neurons and some other cells, a large enough depolarization may result in an action potential
Action potential
In physiology, an action potential is a short-lasting event in which the electrical membrane potential of a cell rapidly rises and falls, following a consistent trajectory. Action potentials occur in several types of animal cells, called excitable cells, which include neurons, muscle cells, and...

. Hyperpolarization
Hyperpolarization (biology)
Hyperpolarization is a change in a cell's membrane potential that makes it more negative. It is the opposite of a depolarization.Hyperpolarization is often caused by efflux of K+ through K+ channels, or influx of Cl– through Cl– channels. On the other hand, influx of cations, e.g...

 is the opposite of depolarization, and inhibits the rise of an action potential.
If, for example, a cell has a resting potential
Resting potential
The relatively static membrane potential of quiescent cells is called the resting membrane potential , as opposed to the specific dynamic electrochemical phenomena called action potential and graded membrane potential....

 of -70mV, once the membrane potential changes to -50mV, then the cell has been depolarized.
Encyclopedia
In biology, depolarization is a change in a cell's membrane potential
Membrane potential
Membrane potential is the difference in electrical potential between the interior and exterior of a biological cell. All animal cells are surrounded by a plasma membrane composed of a lipid bilayer with a variety of types of proteins embedded in it...

, making it more positive, or less negative. In neurons and some other cells, a large enough depolarization may result in an action potential
Action potential
In physiology, an action potential is a short-lasting event in which the electrical membrane potential of a cell rapidly rises and falls, following a consistent trajectory. Action potentials occur in several types of animal cells, called excitable cells, which include neurons, muscle cells, and...

. Hyperpolarization
Hyperpolarization (biology)
Hyperpolarization is a change in a cell's membrane potential that makes it more negative. It is the opposite of a depolarization.Hyperpolarization is often caused by efflux of K+ through K+ channels, or influx of Cl– through Cl– channels. On the other hand, influx of cations, e.g...

 is the opposite of depolarization, and inhibits the rise of an action potential.

Mechanism

If, for example, a cell has a resting potential
Resting potential
The relatively static membrane potential of quiescent cells is called the resting membrane potential , as opposed to the specific dynamic electrochemical phenomena called action potential and graded membrane 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+
Sodium
Sodium is a chemical element with the symbol Na and atomic number 11. It is a soft, silvery-white, highly reactive metal and is a member of the alkali metals; its only stable isotope is 23Na. It is an abundant element that exists in numerous minerals, most commonly as sodium chloride...

 through Na+ channels, or Ca2+
Calcium
Calcium is the chemical element with the symbol Ca and atomic number 20. It has an atomic mass of 40.078 amu. Calcium is a soft gray alkaline earth metal, and is the fifth-most-abundant element by mass in the Earth's crust...

 through Ca2+ channels
Calcium channel
A Calcium channel is an ion channel which displays selective permeability to calcium ions. It is sometimes synonymous as voltage-dependent calcium channel, although there are also ligand-gated calcium channels.-Comparison tables:...

. On the other hand, efflux of K+
Potassium
Potassium is the chemical element with the symbol K and atomic number 19. Elemental potassium is a soft silvery-white alkali metal that oxidizes rapidly in air and is very reactive with water, generating sufficient heat to ignite the hydrogen emitted in the reaction.Potassium and sodium are...

 through K+ channels
Potassium channel
In the field of cell biology, potassium channels are the most widely distributed type of ion channel and are found in virtually all living organisms. They form potassium-selective pores that span cell membranes...

 inhibits depolarization, as does influx of Cl
Chloride
The chloride ion is formed when the element chlorine, a halogen, picks up one electron to form an anion Cl−. The salts of hydrochloric acid HCl contain chloride ions and can also be called chlorides. The chloride ion, and its salts such as sodium chloride, are very soluble in water...

 (an anion) through Cl channels
Chloride channel
Chloride channels are a superfamily of poorly understood ion channels consisting of approximately 13 members.Chloride channels display a variety of important physiological and cellular roles that include regulation of pH, volume homeostasis, organic solute transport, cell migration, cell...

. 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
Voltage
Voltage, otherwise known as electrical potential difference or electric tension is the difference in electric potential between two points — or the difference in electric potential energy per unit charge between two points...

, electrophysiologists
Electrophysiology
Electrophysiology is the study of the electrical properties of biological cells and tissues. It involves measurements of voltage change or electric current on a wide variety of scales from single ion channel proteins to whole organs like the heart...


measure it using current clamp techniques. In voltage clamp
Voltage clamp
The voltage clamp is used by electrophysiologists to measure the ion currents across the membrane of excitable cells, such as neurons, while holding the membrane voltage at a set level. Cell membranes of excitable cells contain many different kinds of ion channels, some of which are voltage gated...

, the membrane currents giving rise to depolarization are either an increase in inward current, or a decrease in outward current.

Depolarization blockers


There are drugs, called depolarization blocking agents, that inhibit depolarization, e.g. by blocking the channels responsible for depolarization, or by opening K+ channels. Examples include the nicotinic agonist
Nicotinic agonist
A nicotinic agonist is a drug which enhances the action at the nicotinic acetylcholine receptor .Examples include:* nicotine...

s suxamethonium and decamethonium
Decamethonium
Decamethonium is a depolarizing muscle relaxant or neuromuscular blocking agent, and is used in anesthesia to induce paralysis.- Pharmacology :...

.

External links

The source of this article is wikipedia, the free encyclopedia.  The text of this article is licensed under the GFDL.
 
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