The transport of vitamin B12 through polarized monolayers of Caco-2 cells.

Caco-2 cells grown on 0.45-micron filters, in Millicell chambers, form intact monolayers with many of the properties of polarized intestinal epithelial cells. It is reported here that these cells bind and internalize intrinsic factor-cobalamin complexes and that after 14-28 days in culture this specific binding is exclusively located on the apical membrane. Caco-2 cells also synthesize and secrete a protein with properties similar to transcobalamin II. This protein is secreted from the basolateral side of the cells after 20 days in culture. Specific apical-to-basolateral transcellular transport of [57Co]cobalamin also occurs between 20 and 28 days in culture. Thus, Caco-2 cells provide the first polarized human cell system for studying the transepithelial transport of cobalamin.