Transepithelial potential difference (TEPD) is the

voltage Voltage, also known as (electrical) potential difference, electric pressure, or electric tension, is the difference in electric potential between two points. In a Electrostatics, static electric field, it corresponds to the Work (electrical), ...

across an

epithelium Epithelium or epithelial tissue is a thin, continuous, protective layer of cells with little extracellular matrix. An example is the epidermis, the outermost layer of the skin. Epithelial ( mesothelial) tissues line the outer surfaces of man ...

, 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. It equals the interior potential minus the exterior potential. This is th ...

s for the outer and inner

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

TEPD in the nose

The diagnosis of

cystic fibrosis Cystic fibrosis (CF) is a genetic disorder inherited in an autosomal recessive manner that impairs the normal clearance of Sputum, mucus from the lungs, which facilitates the colonization and infection of the lungs by bacteria, notably ''Staphy ...

(CF) is usually based on high

chloride The term chloride refers to a compound or molecule that contains either a chlorine anion (), which is a negatively charged chlorine atom, or a non-charged chlorine atom covalently bonded to the rest of the molecule by a single bond (). The pr ...

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

(i.e. the charge on the respiratory

epithelial Epithelium or epithelial tissue is a thin, continuous, protective layer of cells with little extracellular matrix. An example is the epidermis, the outermost layer of the skin. Epithelial ( mesothelial) tissues line the outer surfaces of man ...

surface as compared to

interstitial fluid In cell biology, extracellular fluid (ECF) denotes all body fluid outside the Cell (biology), cells of any multicellular organism. Body water, Total body water in healthy adults is about 50–60% (range 45 to 75%) of total body weight; women ...

). Individuals with cystic fibrosis have a significantly more negative nasoepithelial surface than normal, due to increased luminal sodium absorption. In most

exocrine gland Exocrine glands are glands that secrete substances onto an epithelial surface by way of a duct. Examples of exocrine glands include sweat, salivary, mammary, ceruminous, lacrimal, sebaceous, prostate and mucous. Exocrine glands are one of ...

s, 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 cystic fibrosis, 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 Electrophysiology (from ee the Electron#Etymology, etymology of "electron" ; and ) is the branch of physiology that studies the electrical properties of biological cell (biology), cells and tissues. It involves measurements of voltage change ...

technique widely adopted for use in

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

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 Ohm's law states that the electric current through a Electrical conductor, con ...

resistance to serve as a proxy for the permeability of a cellular monolayer. TEER therefore enables researchers to miniaturize

assay An assay is an investigative (analytic) procedure in laboratory medicine, mining, pharmacology, environmental biology and molecular biology for qualitatively assessing or quantitatively measuring the presence, amount, or functional activity ...

s such as

Caco-2 Caco-2 (from ''Cancer coli'', "colon cancer") is an immortalized cell line of human colorectal adenocarcinoma cells. It is primarily used as a model of the intestinal epithelial barrier. In culture, Caco-2 cells spontaneously differentiate into ...

permeability,

Blood–brain barrier The blood–brain barrier (BBB) is a highly selective semipermeable membrane, semipermeable border of endothelium, endothelial cells that regulates the transfer of solutes and chemicals between the circulatory system and the central nervous system ...

transfer, or membrane integrity assays in

microfluidic Microfluidics refers to a system that manipulates a small amount of fluids (10−9 to 10−18 liters) using small channels with sizes of ten to hundreds of micrometres. It is a multidisciplinary field that involves molecular analysis, molecular bi ...

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