TRANSPORT CHARACTERISTICS OF CEFTIBUTEN, A NEW CEPHALOSPORIN ANTIBIOTIC, VIA THE APICAL H+/DIPEPTIDE COTRANSPORT SYSTEM IN HUMAN INTESTINAL-CELL LINE CACO-2 - REGULATION BY CELL-GROWTH

Purpose. The intestinal epithelial cell line Caco-2 possesses the H+/dipeptide cotransport system responsible for uptake of oral cephalosporins. In this study, the transport characteristics of ceftibuten were examined from the viewpoint of cell growth in the Caco-2 cells. Methods. The uptake of cephalosporins by Caco-2 cell monolayers grown on plastic dishes was measured and analyzed kinetically. Results. The uptake of ceftibuten was increased by lowering pH of the incubation medium and was inhibited by excess dipeptide. The transport activity of ceftibuten was dependent on the duration of culture, being maximal on the 14th day after inoculation. Kinetic analysis revealed that the development of ceftibuten uptake was due to not only a decrease in Km but also to an increase in Vmax value. Conclusions. The uptake of ceftibuten is mediated by the apical H+/dipeptide cotransport system which is regulated by cell growth and/or differentiation in the Caco-2 cells.