LONG-TERM EFFECTS OF TUMOR-NECROSIS-FACTOR ON LLC-PK(1) TRANSEPITHELIAL RESISTANCE

Renal epithelial LLC-PK1 cell sheets incubated with tumor necrosis fac tor (TNF) undergo an acute, spontaneous, and rapidly reversible decrea se in transepithelial resistance (TER). (Mullin et al., 1992). However , 24 to 72 h following TNF exposure, TER across the cell sheet increas es 2-fold. This later effect of TNF is also reversible, albeit slowly. The TER of TNF-treated cell sheets then declines toward initial level s between 72 and 144 h following exposure to the cytokine. Whereas the long-term increase in TER following TNF exposure is not associated wi th a decreased transepithelial C-14-mannitol flux (size selectivity), the charge (anionic) selectivity of the LLC-PK1 tight junction is decr eased. Basal-lateral (ouabain and bumetanide-insensitive) Rb+ and apic al Na+-dependent alpha-methylglucoside (AMG) uptake into the cell are both reduced in cultures exposed to TNF 24 h earlier. Correspondingly, this long-term effect on TER is accompanied by a 30% decrease in shor t circuit current (i(SCC)). Along with an observed increase in basal-l ateral methylamino-isobutyric acid (MeAIB) influx into the cells, an i ncreased incorporation of [H-3]-thymidine into DNA indicates increased cell cycling after exposure to TNF. While the increase in cell cyclin g is not sustained for the duration of the elevation in TER, it does a ppear to initiate a sequence of events that lead to the sustained incr ease in TER. A decrease in the lateral intercellular space, observed b etween these epithelial cells after long-term TNF exposure, may be a m echanism for the elevated TER following from the mitogenesis and/or tr ansport changes. This overall long-term tightening of an epithelium in response to TNF may function, in part, as a compensatory action of th e epithelium to reestablish its effectiveness as a physiological barri er, following the acute effect of TNF. (C) 1993 Wiley-Liss, Inc.