TUMOR-NECROSIS-FACTOR-ALPHA INCREASES SODIUM AND CHLORIDE CONDUCTANCEACROSS THE TIGHT JUNCTION OF CACO-2 BBE, A HUMAN INTESTINAL EPITHELIAL-CELL LINE

CACO-2 BBE was used to determine the response of a gastrointestinal ep ithelium to tumor necrosis factor-alpha (TNF). Incubation of CACO-2 BB E with TNF did not produce any effect on transepithelial resistance (T ER) within the first 6 hr but resulted in a 40-50% reduction in TER an d a 30% decrease in I-sc (short circuit current) relative to time-matc hed control at 24 hr. The decrease in TER was sustained up to 1 week f ollowing treatment with TNF and was not associated with a significant increase in the transepithelial flux of [C-14]-D-mannitol or the penet ration of ruthenium red into the lateral intercellular space. Dilution potential and transepithelial Na-22(+) flux studies demonstrated that TNF-treatment of CACO-2 BBE cell sheets increased the paracellular pe rmeability of the epithelium to Na+ and Cl-. The increased transepithe lial permeability did not associate with an increase in the incidence of apoptosis. However, there was a TNF-dependent increase in [H-3]-thy midine labeling that was not accompanied by a change in DNA content of the cell sheet. The increase in transepithelial permeability was conc luded to be across the tight junction because: (i) 1 mM apical amilori de reduced the basolateral to apical flux of Na-22(+), and (ii) diluti on potential studies revealed a bidirectionally increased permeability to both Na+ and Cl-. These data suggest that the increase in transepi thelial permeability across TNF-treated CACO-2 BBE cell sheets arises from an alteration in the charge selectivity of the paracellular condu ctive pathway that is not accompanied by a change in its size selectiv ity.