Resting Membrane Potential -
Glossary of Key Terms
Refers to the concentration gradient of an ion or molecule. The concentration gradient may exist across a biological membrane, where the concentration is higher on one side of the membrane compared to the other side. Concentration gradient may also exist in a solution without an apparent barrier separating the area of higher concentration from the area of lower concentration. In both cases, the free energy that results from the concentration difference drives the movement of the ion/molcule from the area of higher concentration to the area of lower concentration. In free solution, the ion/molecule simply diffuses down its gradient. Movement across a biological membrane is more complicated and is a function of lipid solubility of the ion/molecule as well as the presence of channels or transport proteins that can allow the ion/molecule to cross the membrane (see Lipid Bilayer Permeability
and Summary of Membrane Transport Processes
Related glossary terms/phrases:Electrical gradientElectrochemical gradient
The flow of charge. In electrical wires and electronic circuits, current is carried by electrons. In physiological solutions, current is carried by ions in solutions.
Related glossary terms/phrases:Voltage
Movement of a substance out of the cell.
Efflux is reported as a rate. It is the amount of substance that moves through a given area of the plasma membrane per unit time.
Related glossary terms/phrases:FluxInfluxUnidirectional fluxNet flux
An electrogenic transport process is one that leads to the translocation of net charge across the membrane. For example, ion channels such as Na+
, and Cl−
channels are electrogenic.
ATPase is electrogenic because for every ATP molecule hydrolyzed, 3 Na+
ions are transported out of the cell and 2 K+
ions are transported into the cell (leading to the translocation of one net positive charge out of the cell).
Many secondary active transporters
are also electrogenic. For example, the Na+
/glucose cotransporter (found in the small intestine and kidney proximal tubules), transports 2 Na+
ions and 1 glucose molecule into the cell across the plasma membrane (leading to the translocation of two net positive charges into the cell per transport cycle).
Electrophysiology is the study of the electrical properties of biological macromolecules, cells, tissues, and organs. Electrical signals such as voltage and/or current are generally measured. Examples include measuring changes in the membrane voltage of excitable cells (e.g., neurons, muscle cells, and some endocrine cells) during an action potential
. The current carrried by ions as they permeate the pore of ion channels can also be measured - both at the single-channel level (single-channel current), as well as the macroscopic current resulting from the activity of a population of channels. As another example, electrical measurements may involve recording voltage changes at the surface of the skin that result from the activity of skeletal muscles (electromyogram, EMG), cardiac myocytes (electrocardiogram, ECG), or neurons in the brain (electroencephalogram, EEG).
Endocrine cells are responsible for producing and releasing hormone
molecules into the bloodstream. Endocrine cells are typically grouped together in organs referred to as endocrine glands
Related glossary terms/phrases:Endocrine glandHormone
Refers to the ability of some cells to be electrically excited resulting in the generation of action potentials
. Neurons, muscle cells (skeletal, cardiac, and smooth), and some endocrine cells (e.g., insulin-releasing pancreatic β
cells) are excitable cells.
See also:Resting Membrane Potential - Introduction
Movement of a substance into the cell.
Influx is reported as a rate. It is the amount of substance that moves through a given area of the plasma membrane per unit time.
Related glossary terms/phrases:FluxEffluxUnidirectional fluxNet flux
The voltage difference across a cell plasma membrane.
The membrane potential is generally inside negative with respect to the outside, where the outside potential is generally set as the reference value. In electrically excitable cells, the value of the membrane potential can be positive (inside with respect to the outside) during electrical activity (i.e., during action potentials).
Related glossary terms/phrases:Resting membrane potential
See also:Resting membrane potential
An equation used to calculate the equilibrium potential (Veq.
) of an ion. The equilibrium potential for an ion is also referred to as the Nernst potential for that ion. It is the membrane potential at which no net movement of the ion in question occurs across the membrane.
is the equilibrium potential, R
is the universal gas constant
is the temperature in Kelvin, z
is the valence of the ionic species, F
is the Faraday's constant
, and [X
are the extracellular and intracellular, respectively, concentrations of the ion in question.
See also:Resting Membrane Potential - Nernst Equilibrium PotentialDerivation of the Nernst Equation
Net flux represents the amount of substance moved in or out of the cell. It is the mathematical difference between influx and efflux.
Net flux = Influx − Efflux
Similar to influx and efflux, net flux is reported as a rate. It is the net amount of substance that moves through a given area of the plasma membrane per unit time.
Related glossary terms/phrases:FluxInfluxEffluxUnidirectional flux
Ouabain binds to and inhibits the transport activity of the Na+
/ATPase (i.e., sodium pump).
Ouabain is plant derived and belongs to the class of drugs referred to as cardiac glycosides. Similar to other cardiac glycosides, ouabain increase heart muscle contractility. However, ouabain is used only experimentally and not in humans (as for example digoxin is for the treatment of congestive heart failure).
There is some evidence that ouabain may be produced endogenously in humans.
Related glossary terms/phrases:Vanadate
Other resources:Ouabain (Wikipedia)
Resting membrane potential
The voltage difference across a cell plasma membrane in the resting or quiescent state. It is also simply referred to as the resting potential (Vrest
). The value of the resting membrane potential varies from cell to cell. Depending on the cell type, it can range from −90 mV to −20 mV.
For example, Vrest
is −90 mV in skeletal and cardiac muscle cells as well as in astrocytes. In a typical neuron, Vrest
is approximately −70 mV. In many non-excitable cells, Vrest
ranges from −60 to −50 mV. In photoreceptors, Vrest
is about −20 mV.
See also:Resting membrane potential
An inhibitor of the Na+
/ATPase (i.e., sodium pump). The form commonly used for this purpose is sodium orthovanadate.
Related glossary terms/phrases:Ouabain
The difference in electrical potential between two points.
Posted: Saturday, February 15, 2014
Last updated: Saturday, November 21, 2015