CELL-POLARITY DEPENDENT EFFECT OF CHELATION ON THE PARACELLULAR PERMEABILITY OF CONFLUENT CACO-2 CELL MONOLAYERS

To investigate the effect of extracellular chelation at the apical, ba solateral or both sides on the resistance and permeability of epitheli al cell layers, we used 15 days cultures of a human intestinal adenoca rcinoma cell line (Caco-2) and hydrophilic FITC-labeled dextran model compounds of various molecular weights. Transport of these hydrophilic compounds is restricted to the paracellular pathway in which the tigh t junctions form a barrier. Tight junctions are dependent on extracell ular calcium and magnesium for their integrity and function. Calcium a nd magnesium chelation with 2.5 mM EDTA at the apical and basolateral side of the monolayer resulted in a drastic drop, up to 80% of the ini tial value, in trans-epithelial electrical resistance after 60 min. Ap plication at the basolateral side resulted in a drop of 40% in resista nce, while application on the apical side almost did not give any effe ct. The same pattern was also found in transepithelial clearance studi es with fluorescein-Na and FITC-labeled dextran model compounds with m olecular weights ranging from 4000 to 500000. After 2.5 mM EDTA treatm ent on both sides a maximal (1400-fold) enhancement in transport clear ance occurred for the dextran molecule with molecular weight 20000 (St okes-Einstein molecular radius 30 angstrom). For basolateral calcium a nd magnesium chelation similar results were found, however, with lesse r maximal effects. For apical application no transport enhancement cou ld be found with 2.5 mM EDTA. These results have shown that transport of hydrophilic compounds through epithelial monolayers is enhanced mor e effectively by basolateral application of EDTA than by apical applic ation.