In Vitro Methods for Measuring the Permeability of Cell Monolayers

Abstract

Cell monolayers, including endothelial and epithelial cells, play crucial roles in regulating the transport of biomolecules to underlying tissues and structures via intercellular junctions. Moreover, the monolayers form a semipermeable barrier across which leukocyte transmigration is tightly regulated. The inflammatory cytokines can disrupt the epithelial and endothelial permeability, thus the reduced barrier integrity is a hallmark of epithelial and endothelial dysfunction related with numerous pathological conditions, including cancer-related inflammation. Therefore, the assessment of barrier function is critical in in vitro models of barrier-forming tissues. This review summarizes the commercially available in vitro systems used to measure the permeability of cellular monolayers. The presented techniques are separated in two large groups: macromolecular tracer flux assays, and electrical impedance measurement-based permeability assays. The presented techniques are briefly described and compared.

Keywords: dysfunction; endothelium; epithelium; fluorescent tracer; microfluidics; permeability; transendothelial resistance.

Figure 1

The overview of a transwell support system (taken from https://tumomics.creative-proteomics.com/, accessed on 28 June 2021, with permission).

Figure 2

The overview of EVOM3 (epithelial volt–ohm meter) system with all its components, used for the transepithelial/transendothelial electrical resistance (TEER) measurements (from left to right: A/C power supply and charger, STX2-Plus electrode, EVOM3 meter and the optional Endohm-6G chamber electrode). (A) the general view of the whole EVOM3 system. (B) The EVOM3 meter with the 1 kOhm test resistor inserted into the electrode port: the display shows the actual resistance of the test resistor. (C) The body of the STX2-Plus chopstick electrode. (D,E) The proper adjustment of STX2-Plus electrode to fit the insert with a 6.5 mm diameter (compatible with 24-well plates): the outer electrode reaches close to the bottom of the well plate, while the inner electrode is close to the membrane inside the insert, without touching it. (F) The Endohm-6G chamber electrode with the 6.5 mm cell culture insert inside the chamber, connected with the EVOM3 meter by the Endohm cable. (G) The detailed view of the Endohm-6G chamber with the cell culture insert.

Figure 3

Schematic drawing of a circulating Ussing chamber (taken from [30], license no. 5112401256947).