Transepithelial Electrical Resistance Measurements

For TER measurements, cells were plated at confluency in Transwell inserts and grown in NC medium. TER was measured in confluent cell monolayers subjected to a Ca²⁺ switch. In this case, rapid TJ disassembly, as assessed by obtaining background TER values, was induced by incubating confluent cell monolayers for 1 h in Ca²⁺-deprived LC medium containing 1 mM EGTA; cells were then switched back to NC medium for the indicated time, as described previously (Nunbhakdi-Craig et al., 2002 (link)). In other experiments, cells were plated at confluency in Transwell inserts and cultured for 72 h in NC medium to allow complete TJ maturation. Transfected protein expression was induced with sodium butyrate as soon as cells were attached. For each time point, TER was measured using an Epithelial Volt/Ohm Meter (EVOM²; World Precision Instruments). Particular care was taken to measure TER under strictly similar experimental conditions across cell lines (Sheller et al., 2017 (link)). TER values (Ω.cm²) were normalized to the filter area of the monolayer and calculated by subtracting blank values from the filter and bathing medium (Nunbhakdi-Craig et al., 2002 (link)).