TRANSEPITHELIAL TRANSPORT OF ORAL CEPHALOSPORINS BY MONOLAYERS OF INTESTINAL EPITHELIAL-CELL LINE CACO-2 - SPECIFIC TRANSPORT-SYSTEMS IN APICAL AND BASOLATERAL MEMBRANES

The accumulation and the transepithelial transport of p.o. cephalosporins by monolayers of human intestinal epithelial cell line Caco-2 grown on microporous membrane filters were evaluated. Cephradine was accumulated concentratively in the monolayers from the apical side, and was transported to the basolateral side. The accumulation and the apical-to-basolateral transport of cephradine were temperature-dependent and sensitive to the pH of the apical side, with the optimal pH 6.0 to 6.5. The efflux of cephradine from the monolayers to the basolateral side was also temperature-dependent and was more rapid than its efflux to the apical side. The accumulation and the apical-to-basolateral transport of cephradine, cephalexin and cefixime, all p.o. agents, were significantly higher than those of cefotiam, a parenteral agent. The apparent K(m) and V(max) values for cephradine accumulation were 8.3 mM and 2.49 nmol/mg of protein per min, respectively. Dipeptides inhibited the accumulation and the apical-to-basolateral transport of cephradine. Both the accumulation and the efflux of cephradine in the monolayers were inhibited significantly by the sulfhydryl reagent p-chloromercuribenzene sulfonate. These findings suggest that p.o. cephalosporins accumulate in the Caco-2 cell monolayers via the H+/dipeptide cotransport system localized in the apical membranes and that a specific transport system is involved in the efflux of these antibiotics across the basolateral membranes.