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Cell potential

In biological cells that are electrically "at rest," the cytosol possesses a uniform electric potential or voltage of about - 0.1 V or -100 mV compared to the extracellular solution. This voltage is the resting cell potential, also sometimes called the transmembrane potential of the resting cell. Between the inside and outside of the cell (which like the cytosol is typically uniform electrically) the voltage rises very steeply just at the boundary created by the membrane. This gives rise to the transmembrane electric field[?], which exerts a force on ions and controls voltage-gated ion channels. Integral membrane proteins such as channels, pumps, and exchangers establish the membrane potential by transporting specific ions in or out. In essence, resting cells are negative because positively charged potassium ions, which are more concentrated inside than outside, are allowed to leak out. The resulting negative voltage difference between inside and out is therefore approximately equal to the reversal potential for potassium. Sodium-potassium exchangers maintain intracellular potassium at a high concentration while pumping sodium into the extracellular solution, where the concentration of sodium typically is high.

When a cell is "excited," as occurs in neurons during an archetypical action potential, sodium ions rush into the cell through sodium channels, depolarizing the cell (i.e. making the cell potential less negative). Excitability is central to the function of neurons and muscle cells and also figures in the initial response of an egg to fertilization by a sperm. The study of the electrical properties of biological membranes belongs to electrophysiology or biophysics.

While cells expend energy to transport ions and establish a transmembrane potential, they use this potential in turn to transport other ions and metabolites such as sugar. The transmembrane potenial of the mitochondria drives the prodution of ATP, which is the common currency of biological energy.

See also action potential
Compare electrochemical potential



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