Choosing the Right EVOM Electrode for TEER Measurements

This video demonstrates how to establish a liquid-covered culture of polarized human airway epithelial Calu-3 cells using a transwell culture system, where cells are seeded into the apical compartments and cultured for 2-3 weeks with media changes on a 3-4 day cycle, followed by verification of polarization through trans-epithelial electrical resistance and passive sodium fluorescein equilibration assays; Calu-3 cells are preferred over normal human bronchial epithelial cells because they are more accessible and develop more rapidly into depolarized cultures ready for use.

A hanging insert system (such as the Millicell system from EMD Millipore) allows researchers to grow primary endometrial epithelial cells in a polarized configuration. The epithelial cells are grown on inserts coated with Matrigel to replicate basal lamina components. Once confluent, these inserts are placed in standard 24-well plates containing patient-paired fibroblasts in the lower chamber. This setup enables measurement of basolateral secreted products from epithelial cells affecting underlying stromal fibroblasts, while also allowing assessment of stromal factors on epithelium.

Cell culture inserts are membrane-based devices containing semi-permeable membranes that split the culture chamber into apical and basolateral compartments, enabling cell polarization, co-culturing, and permeability assays. These inserts feature track-etched microporous membranes produced by breaking polymer molecular chains with accelerated noble gas ions to create defined pore channels, which are then chemically etched and treated with air plasma for optimal cell attachment. The quality of these membranes is critical for reproducible cell culture experiments, requiring uniform pore distribution, proper coating, and even welding to the plastic body. Membrane pore size selection depends on the application: 0.4-1 micron for epithelial and endothelial layers, while 3-8 micron sizes are suitable for migration and invasion studies. Clear membranes are preferred for phase contrast microscopy monitoring, while translucent membranes support faster cell growth. These membrane-based systems are widely used to model biological barriers including the blood-brain barrier, intestinal and respiratory epithelia, skin, hepatic and renal epithelia, and placental barrier, as well as for permeability and toxicity testing of drugs, chemicals, and cosmetics.

Membrane platforms enable long-term polarized cell culture that more closely resembles in vivo conditions compared to conventional plastic surfaces. For example, 21-day CaCo-2 cell cultures on 0.4-micron polycarbonate membranes produce cells with dramatic differences from those grown on plastic surfaces, exhibiting polarized morphologies characteristic of intestinal epithelium. Confocal imaging reveals the three-dimensional organization and functional polarization achieved through membrane-based culture systems, demonstrating their value for modeling epithelial physiology and barrier function.

Millicell® cell culture insert plates are membrane-based devices with 10-micron thickness and defined pore sizes, used to create in vitro models for air-liquid interface, blood-brain barrier, intestinal barrier (Caco-2), and cellular migration/invasion assays; they feature apical assist technology that creates a membrane-free area for safe apical media exchange without disturbing cells or puncturing the membrane, along with basolateral access ports for media exchange, available in 24-well and 96-well formats with either single-well feeder trays for initial cell culturing or multi-role receiver plates for individualized assay treatments.

Ohm's Law states that current is directly proportional to potential difference: V = IR, where V is voltage, I is current, and R is resistance. Resistance is the opposition to current flow. Higher resistance means less current flows. The unit of charge is Coulomb (C), voltage is Volt (V), and current is Ampere (A). 1 Volt = 1 Joule per Coulomb, and 1 Ampere = 1 Coulomb per second.

Ohm's Law states that if the physical state of a conductor remains unchanged, the current flowing through it is directly proportional to the potential difference applied across its ends (V ∝ I). This leads to V = IR, where R is the constant of proportionality called resistance. Resistance is defined as the opposition offered by a conductor to the flow of electric current, given by R = V/I. Resistance is a scalar quantity (अदिश राशि) with SI unit Ohm (Ω). The dimensional formula is [M^1 L^2 T^-3 A^-2].

Ohm's Law states that the current flowing through a conductor is directly proportional to the potential difference across its ends, provided physical conditions remain constant: V = IR, where V is potential difference, I is current, and R is resistance. Resistance is the opposition to current flow. The SI unit of resistance is the ohm (Ω). Resistance depends on: (1) Length - directly proportional; (2) Cross-sectional area - inversely proportional; (3) Material - different materials have different resistivities; (4) Temperature - resistance increases with temperature for most conductors. Formula: R = ρL/A.

Electrical resistance (R) is the opposition to current flow, measured in Ohms (Ω). Ohm's Law states that current is directly proportional to voltage at constant temperature: V = IR. The Ohm's Law triangle (V at top, I and R at bottom) helps solve for any variable: V = IR, I = V/R, or R = V/I. This fundamental law governs the behavior of most electrical circuits and is essential for circuit analysis.

Ohm's Law states that current (I) equals voltage (V) divided by resistance (R): I = V/R. Resistance opposes current flow and depends on material, length, and cross-sectional area. Fixed resistors have constant resistance, while variable resistors (rheostats) allow adjustment. The Ohm's Law triangle helps remember relationships: V = IR, I = V/R, R = V/I. Direct current (DC) flows in one direction with constant magnitude, produced by batteries. Alternating current (AC) periodically reverses direction and changes magnitude, produced by generators.

The EVOM Manual is WPI's instrument for measuring Trans Epithelial Electrical Resistance (TEER); to use it, first power on the device and insert the USB flash drive, then configure file naming by choosing between auto-indexed prefixes or unique filenames, select your plate size and measurement units (volts or millivolts), equilibrate electrodes in liquid for at least three hours, perform a null offset by pressing the probe null button until the solution value reads 0.0, enable the offset function, and begin measurements by pressing the foot switch or store button, storing data files on the USB drive for later analysis on a computer.

Transepithelial Electrical Resistance (TEER) is a well-established technique used to assess the barrier function and integrity of epithelial and endothelial cell layers by applying a small AC current to the cell monolayer and measuring the resistance to ion flow, providing valuable insights into tight junction integrity and cell-cell interactions; WPI's EVOM family of meters, including manual and automated systems for 24-well and 96-well plates, serves as the gold standard in TEER technology, having been trusted for nearly 40 years and cited in thousands of peer-reviewed publications for applications in drug absorption studies, tissue engineering, disease modeling, and quality control.

This comprehensive workflow covers the entire process of measuring trans-epithelial electrical resistance (TEER) in air-liquid interface (ALI) cultures using an epithelial volt ohm meter (EVOM). The procedure begins with probe sterilization in 70% isopropanol for 15 minutes, followed by washing in sterile PBS. ALI cultures are prepared by removing medium and adding calcium/magnesium-free PBS to the apical compartment and regular PBS to the basal compartment. The probe is inserted at a 90-degree angle into the transwell hanger, with the long tongue touching the bottom and the short prong resting above the culture surface. Ohm values are recorded after stabilizing, then the probe is washed and moved to the next culture. After completing measurements, the probe is returned to IPA, PBS is removed, and culture medium is restored. The blank transwell control is measured last, and the probe undergoes final cleaning before storage.

Modern epithelial volt/ohm meters for TEER (Transepithelial Electrical Resistance) measurement offer significant advantages over older models, including faster stabilization times, higher resolution readings (down to 0.1 ohm), reduced electrical noise through battery power, intuitive touchscreen interfaces for setup and data navigation, and automatic data storage capabilities that eliminate manual data transfer requirements.

WPI's EVOM Manual provides stable and repeatable trans epithelial electrical resistance (TEER) measurements for assessing cell monolayer integrity; the system offers multiple electrode options including the STX4 general-purpose electrode with replaceable blades for 24-well plates, and STX HTS electrodes designed for high-throughput screening in 24 and 96-well plates, along with end dome cell culture cup chambers available in 6mm, 12mm, and 24mm sizes for different well plate formats.