Our bodies contain specialized cellular barriers that control substance movement. These barriers are layers of tightly connected cells, forming protective interfaces in various organ systems. Scientists use specific techniques to understand how these barriers function. The Transepithelial Electrical Resistance (TEER) assay is a widely adopted method. It quantitatively assesses cellular barrier integrity, providing insights into their health and permeability.
The Importance of Cellular Barriers
Cellular barriers, composed of epithelial and endothelial cells, serve as protective linings. Epithelial tissues cover external organ surfaces and line cavities, while endothelial cells form the inner lining of blood and lymphatic vessels. These layers maintain the internal environment, regulate molecule passage, and prevent harmful substances from entering tissues.
The gut lining acts as a selective filter, allowing nutrient absorption while blocking pathogens and toxins. The blood-brain barrier safeguards the brain from detrimental circulating substances. The skin, a multi-layered epithelial barrier, protects against physical damage, dehydration, and microbial invasion. Maintaining barrier integrity is fundamental for health, as compromise can lead to diseases and dysfunctional processes.
What Trans-Epithelial Electrical Resistance Measures
Trans-Epithelial Electrical Resistance (TEER) quantifies electrical resistance across a cell monolayer, indicating the tightness of cell junctions. This measurement reflects the opposition to ion flow through the paracellular pathway, the space between adjacent cells. Intercellular connections, particularly tight junctions, regulate the passage of ions and small molecules.
A more intact barrier offers greater resistance to electrical current, as there are fewer open pathways for ions. Higher TEER values indicate a tighter, more functional barrier. Conversely, lower TEER values suggest a compromised barrier with looser junctions and increased permeability. This correlation makes TEER a reliable, quantitative measure for assessing epithelial and endothelial barrier integrity in laboratories.
The TEER Measurement Process
Measuring TEER in a laboratory involves culturing cells on specialized inserts, often referred to as transwells. These inserts feature a porous membrane that allows cells to grow as a monolayer, mimicking a biological barrier. Once the cells form a confluent layer, electrodes are used to measure the electrical resistance across this cellular sheet.
A common setup utilizes a voltohmmeter and a “chopstick” electrode pair. One electrode is placed in the upper chamber of the transwell, in contact with the apical side of the cell monolayer, while the other is placed in the lower chamber, touching the basolateral side. A small alternating current (AC) voltage signal, often at 12.5 Hz, is applied across the cell layer, and the resulting voltage drop is measured.
Resistance is then calculated using Ohm’s law (V=IR), and the background resistance from the culture insert and medium is subtracted to obtain the true TEER value. Consistent electrode placement, maintaining a stable temperature around 37°C, and regular calibration of the equipment are important for obtaining accurate and reproducible readings.
Where TEER Assays Are Used
TEER assays find broad application in scientific research and drug development, quantifying cellular barrier integrity. In pharmaceutical research, TEER assesses drug absorption, evaluating how effectively a compound crosses biological barriers like the intestinal lining to reach systemic circulation. This helps predict a drug’s bioavailability and efficacy.
The assay is valuable in toxicity testing, where researchers evaluate the impact of substances on barrier function. A decrease in TEER after compound exposure can indicate cellular damage or barrier compromise. TEER assays are also employed in disease modeling to study conditions where barrier function is impaired, such as inflammatory bowel disease, neurological disorders affecting the blood-brain barrier, or respiratory conditions. This allows scientists to understand disease mechanisms and test potential therapeutic compounds aimed at restoring or enhancing barrier integrity.