Transepithelial potential difference (TEPD) is the

voltage Voltage, also known as electric pressure, electric tension, or (electric) potential difference, is the difference in electric potential between two points. In a static electric field, it corresponds to the work needed per unit of charge to ...

across an

epithelium Epithelium or epithelial tissue is one of the four basic types of animal tissue, along with connective tissue, muscle tissue and nervous tissue. It is a thin, continuous, protective layer of compactly packed cells with a little intercellul ...

, and is the sum of the

membrane potential Membrane potential (also transmembrane potential or membrane voltage) is the difference in electric potential between the interior and the exterior of a biological cell. That is, there is a difference in the energy required for electric charges ...

s for the outer and inner

cell membrane The cell membrane (also known as the plasma membrane (PM) or cytoplasmic membrane, and historically referred to as the plasmalemma) is a biological membrane that separates and protects the interior of all cells from the outside environment (t ...

TEPD in the nose

The diagnosis of

cystic fibrosis Cystic fibrosis (CF) is a rare genetic disorder that affects mostly the lungs, but also the pancreas, liver, kidneys, and intestine. Long-term issues include difficulty breathing and coughing up mucus as a result of frequent lung infections. Ot ...

(CF) is usually based on high

sweat Perspiration, also known as sweating, is the production of fluids secreted by the sweat glands in the skin of mammals. Two types of sweat glands can be found in humans: eccrine glands and apocrine glands. The eccrine sweat glands are distrib ...

chloride The chloride ion is the anion (negatively charged ion) Cl−. It is formed when the element chlorine (a halogen) gains an electron or when a compound such as hydrogen chloride is dissolved in water or other polar solvents. Chloride s ...

concentrations, characteristic clinical findings (including sinopulmonary infections), and/or family history. However, a small portion of patients with cystic fibrosis especially those with "mild" mutations of the cystic fibrosis transmembrane regulator (CFTR) ion channel, have near-normal sweat tests. In these cases, a useful diagnostic, adjunct involves measuring the nasal transepithelial potential difference (ie, the charge on the respiratory epithelial surface as compared to interstitial fluid). Individuals with cystic fibrosis have a significantly more negative nasoepithelial surface than normal, due to increased luminal sodium absorption. In most exocrine glands, the CFTR protein normally secretes chloride ions into the lumen, and also has a tonic inhibitory effect on the opening of the apical sodium channel (which absorbs sodium into the cell). Impaired CFTR functioning directly reduces ductal epithelial chloride secretion and indirectly increases sodium absorption through lack of CFTR's inhibitory effect on the apical sodium channel. The result is dehydrated mucus and a widened, negative transepithelial potential difference. The

nasal Nasal is an adjective referring to the nose, part of human or animal anatomy. It may also be shorthand for the following uses in combination: * With reference to the human nose: ** Nasal administration, a method of pharmaceutical drug delivery * ...

TEPD is increased in

, making it a potential diagnostic tool for this disorder.

TEPD in the kidney

In the kidney, TEPD contributes to tubular reabsorption.

TEER Measurement

Transepithelial / transendothelial electrical resistance (TEER) is an electrophysiological technique widely adopted for use in

Organ-on-a-chip An organ-on-a-chip (OOC) is a multi-channel 3-D microfluidic cell culture, integrated circuit (chip) that simulates the activities, mechanics and physiological response of an entire organ or an organ system, a type of artificial organ. It constit ...

systems. It uses

Ohmic contact An ohmic contact is a non-rectifying electrical junction: a junction between two conductors that has a linear current–voltage (I–V) curve as with Ohm's law. Low-resistance ohmic contacts are used to allow charge to flow easily in both direct ...

resistance to serve as a proxy for the permeability of a cellular monolayer. TEER therefore enables researchers to miniaturize assays such as Caco-2 permeability,

Blood–brain barrier The blood–brain barrier (BBB) is a highly selective semipermeable border of endothelial cells that prevents solutes in the circulating blood from ''non-selectively'' crossing into the extracellular fluid of the central nervous system where ne ...

transfer, or membrane integrity assays in Microfluidic systems. TEER has proven to be a highly sensitive and reliable method to confirm the integrity and permeability of ''in vitro'' barrier models. Because it is non-invasive and offers the advantage of continuously monitoring living cells throughout their various stages of growth and differentiation, it is widely accepted as a standard validation tool.

References

{{Reflist Membrane biology Cystic fibrosis