2.9. Trans-Epithelial Electrical Resistance (TEER) Assay

This assay was carried out by following previously laid down protocols [34] with a few modifications. The electrical resistance was measured across the monolayers (from the apical to the basolateral sides) using a Millicell ERS-2 electrode (MERSSTX01) volts/ohmmeter resistance system (Millipore Corporation, Bedford, MA, USA). To obtain the true resistance values, the background resistance for the cell culture membrane inserts with (the serum- and antibiotic-free) medium was subtracted from the initial and final resistance readings. The TEER value was obtained as a product of the resistance value and the cell culture insert membrane area in cm².