Paracellular Transport in the Mouse Kidney Cortical Collecting Duct Epithelial Monolayers Can Be Monitored By Measuring Transepithelial Resistance
Authors: Nag Subhra , Resnick Andrew 
Published: June 2021

Kidney epithelial cells help to maintain barrier function and selectively allow transport of ions and molecules through transcellular and paracellular routes. In renal epithelial monolayers, transepithelial resistance (TER) shows a stable electrical read‐out and is generally assumed to be an indicator of cellular health and transport. TER represents a composite value of paracellular and transcellular resistance, taken in parallel. We hypothesize that TER values of epithelial monolayers can be a useful parameter to determine transport through paracellular routes in renal epithelial cell lines with high TER values of monolayers and have limitations to determine cell viability. We compared two different kidney epithelial cell lines, a mouse kidney cortical duct cell line, mCCD 1296(d) having high monolayer TER values of around 3 kΩ‐cm2, and Madin‐Darby Canine Kidney (MDCK) epithelial cells, a widely used cell line, having monolayer TER values around 500 Ω‐cm2. Cells were first grown onto permeable membranes and then monolayers were allowed to undergo differentiation. We used Endohm (Ussing) chambers to record TER values of differentiated monolayers. FITC‐conjugated dextran molecules (3 kDa and 70 kDa) were used to quantify transepithelial transport in terms of permeability values. Permeability of 70 kDa dextran molecules estimated the paracellular transport since the transport of these large‐size dextran molecules are restricted only through paracellular routes, not by fluid phase transcytosis. Pearson's correlation showed that the permeability of mCCD monolayers maintained a fair and statistically significant negative correlation with TER values, whereas, MDCK monolayers showed a poor and non‐significant correlation. Therefore, TER values will be useful indicator of the paracellular transport of monolayers of specific renal epithelial cell line having high TER values, such as mCDD cells. Moreover, we recently reported that Hypoxia Inducible Factor 1α (HIF1α) stabilization decreases TER and increases permeability in mCCD monolayers [1]. Surprisingly, in MDCK monolayers, we noticed both TER values and permeability increased due to HIF1α stabilization, supporting that TER is not an ideal parameter to compare paracellular transport of MDCK monolayers.In another set of experiments in mCCD monolayers, different cell seeding numbers showed significantly different MTT cell viability but not significantly different TER values, suggesting that same level of viability does not ensure the equivalent TER values. However, TER values and MTT cell viability of mCCD cells showed moderate and statistically significant correlation when cellular monolayers had TER values less than 1000 Ω‐cm2. Thus, TER measurements can be useful in determining cell viability when paracellular resistance is negligible. We also noticed that transcellular sodium transport was altered by the presence of fluid flow due to ciliary mechanosensation but TER values remained unchanged, indicating fluid flow does not affect paracellular transport. Epithelial tight junction proteins are known to control the transport through paracellular routes. Thus, measurement of TER values can be useful to monitor the functionality of epithelial tight junctions of mCCD cells.Support or Funding InformationNational Institute of Diabetes and Digestive and Kidney Diseases 1R15DK092716 to AR and Cleveland State University Dissertation Research Award to SN.This abstract is from the Experimental Biology 2018 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.