Transepithelial Electrical Resistance: Epithelial Barrier Insight

Transepithelial electrical resistance (TEER) is a widely used technique for assessing the integrity of epithelial and endothelial barriers. These barriers regulate ion and molecule passage, playing a crucial role in physiological processes such as nutrient absorption, immune defense, and drug permeability studies. TEER provides a quantitative measure of barrier tightness, making it valuable in research and pharmaceutical applications.

Principles Of Measurement

TEER quantifies the integrity of epithelial and endothelial monolayers by measuring electrical resistance across a cell layer. This resistance reflects the tightness of intercellular junctions, particularly tight junctions, which regulate paracellular ion flow. The measurement is performed using electrodes placed on either side of a cell culture insert, with a small voltage applied to determine the resulting current. Ohm’s law (V = IR) is then used to calculate resistance.

Accuracy depends on factors like electrode placement, culture conditions, and medium composition. Electrodes must be positioned consistently to ensure reproducible readings. The culture medium’s ionic composition influences resistance values, necessitating standardized solutions. Temperature fluctuations also impact readings, as electrical resistance is temperature-dependent, so measurements should be conducted at 37°C.

Electrode calibration is critical, as electrodes can accumulate biofilm or experience drift, leading to inaccurate readings. Regular calibration using known resistances maintains precision. Additionally, background resistance from the culture insert and medium must be subtracted to obtain the true TEER value, ensuring the reported resistance reflects only the monolayer’s contribution.

Relevance To Epithelial Barrier Function

TEER serves as a quantitative indicator of epithelial barrier integrity, offering insights into how well cellular layers regulate permeability. The epithelial barrier controls the movement of ions, solutes, and water while preventing harmful substances from passing through. TEER measurements reflect the resistance of tight junctions, the primary structural component of the paracellular pathway. A high TEER value indicates a well-maintained barrier, while a decrease suggests compromised integrity due to inflammation, chemical exposure, or disease-related dysfunction.

TEER is widely used to monitor dynamic changes in barrier properties under physiological and pathological conditions. In inflammatory bowel disease (IBD), for example, barrier dysfunction is characterized by reduced TEER due to increased permeability. Pro-inflammatory cytokines like tumor necrosis factor-alpha (TNF-α) and interferon-gamma (IFN-γ) disrupt tight junction proteins, leading to a measurable decline in resistance. TEER helps evaluate potential therapeutic agents aimed at restoring barrier function.

Beyond disease modeling, TEER assesses the impact of pharmaceutical compounds on epithelial permeability. The intestinal epithelium serves as a checkpoint in drug absorption, and TEER measurements help determine whether a compound enhances or disrupts barrier properties. Nanoparticle-based drug delivery research uses TEER to evaluate epithelial interactions, ensuring permeability modifications do not compromise the barrier. In pulmonary models, TEER assesses inhaled drug formulations and their effects on airway barrier function.

Laboratory Setup And Procedures

A reliable TEER measurement setup requires careful selection of equipment, culture conditions, and procedural consistency. Permeable support inserts, typically made of polycarbonate or polyester membranes, provide a surface for cells to form a confluent monolayer. These inserts are housed in multi-well plates, allowing simultaneous testing of multiple conditions. Membrane pore size and coating material influence cell attachment, differentiation, and junction formation, all of which impact TEER readings.

Once the monolayer reaches confluence, resistance is measured using chopstick electrodes or an EndOhm chamber. Chopstick electrodes allow quick measurements, while EndOhm chambers provide uniform current distribution, reducing variability. Electrodes must be sterilized and calibrated before each use, as protein deposition and biofilm formation can alter readings. The culture medium should be warmed and equilibrated to minimize fluctuations from temperature shifts or ion imbalances.

TEER values are recorded over time to track barrier maturation or response to experimental conditions. Readings should be taken consistently, avoiding disturbances like excessive liquid handling or mechanical stress from electrode insertion. Baseline resistance of the cell-free insert and medium must be subtracted to obtain the true TEER value. Triplicate measurements per well and replicate wells per condition enhance data reliability, reducing the impact of outliers.

Factors Influencing TTE

TEER measurements are shaped by biological and technical factors affecting monolayer integrity and resistance values. The type of epithelial or endothelial cells used is a key determinant, as different cell lines exhibit varying baseline resistances. Caco-2 cells, commonly used in intestinal permeability studies, typically generate TEER values between 200 and 1000 Ω·cm², whereas brain microvascular endothelial cells, which form the blood-brain barrier, can exceed 1000 Ω·cm² due to their highly selective tight junctions. Monolayer confluence and differentiation state also impact resistance, with incomplete coverage or immature junctions leading to artificially low readings.

Environmental conditions further influence TEER variability. Temperature fluctuations alter ion mobility and membrane conductivity, making a stable 37°C environment essential. pH shifts in the culture medium can affect junctional integrity, particularly in gastrointestinal or pulmonary models. The medium’s composition, including calcium and magnesium ions, is also critical, as their depletion weakens tight junctions. Serum components and growth factors may modulate TEER by strengthening or weakening intercellular adhesion, depending on their effects on cell signaling pathways.

Interpreting TTE Data

Analyzing TEER data requires accounting for biological variability, experimental conditions, and potential confounding factors. Raw resistance values must be normalized to surface area, typically expressed in Ω·cm², to ensure comparability across different well sizes and setups. Normalization helps distinguish genuine changes in barrier integrity from artifacts introduced by variations in electrode placement or insert dimensions. A consistent baseline measurement before applying treatments is crucial, as initial fluctuations can influence interpretations.

Longitudinal TEER monitoring provides insights into barrier dynamics over time, particularly in response to pharmacological agents or pathological stimuli. A gradual increase in resistance may indicate enhanced tight junction formation, while a sharp decline often signals barrier disruption due to cytotoxic effects or inflammation. Differentiating between transient and sustained changes is essential, as temporary drops may result from reversible alterations in tight junction protein expression, while persistent reductions could indicate structural damage. Researchers often complement TEER data with immunostaining for tight junction markers like occludin and ZO-1 or permeability assays using fluorescent tracers to validate findings.