ROLE OF REDOX SYSTEMS ON FE3-2) CELLS( UPTAKE BY TRANSFORMED HUMAN INTESTINAL EPITHELIAL (CACO)

Caco-2 cells were used as a model of human intestinal epithelium to in vestigate the role of redox systems in transepithelial transport of Fe -59(3+). The cells reduced Fe3+ present in the apical medium; the redu ction was 50% inhibited by adriamycin and p-chloromercuribenzoate. Add ition of [C-14]ascorbate to the basolateral medium resulted in accumul ation of C-14 radioactivity in both cells and apical medium; apical ra dioactivity increased with time and was probably caused by paracellula r flux. The cells provided Fe3+ reduction capacity to the apical incub ation medium. Addition of ascorbate to the basolateral medium increase d this reduction capacity a-fold and the cellular uptake of Fe-59(3+) 1.8-fold. Adriamycin significantly inhibited both cellular Fe-59 uptak e and Fe transport into the basolateral side. The results indicate tha t Caco-2 cells reduce apical Fe3+ by two parallel mechanisms: by a pla sma membrane ferrireductase and by the secretion of reductants of eith er cellular or basolateral origin. The data support a model for Fe3+ i ntestinal absorption in which cell-mediated Fe3+ reduction occurs befo re cellular Fe uptake.