THE EFFECT OF APOTRANSFERRIN ON IRON RELEASE FROM CACO-2 CELLS, AN INTESTINAL EPITHELIAL-CELL LINE

The Caco-2 cell line grown in bicameral chambers was used to study the effect of transferrin in the basal chamber on the transepithelial tra nsport of iron. We have shown that when iron was offered as Fe-59 on t he apical surface of the Caco-2 cells, transport of Fe-59 into the bas al chamber was stimulated by 50 mu mol/L apotransferrin. Here, we exam ined the effect on Fe-59 transport of lower concentrations of apotrans ferrin, as well as the effects on transport of ovo-, cobalt-, and ferr i-transferrin and of iron chelators with an affinity for iron greater than that of transferrin. The stimulation of Fe-59 transport was more sensitive to the presence of apotransferrin with a K-m of 0.078 +/- 0. 008 mu mol/L compared with ferri-transferrin with a K-m of 1.24 +/- 0. 39 mu mol/L (P < .006). Fe-59 transport was less sensitive to diethyle netriaminopentaacetic acid (DTPA) than apotransferrin with K(m)s of 1. 52 +/- 0.70. The chelator nitrilotriacetic acid (NTA) exhibited no sti mulation of Fe-59 transport. Analysis of laser scanning confocal micro graphs showed that apotransferrin labeled with Texas Red is internaliz ed by Caco-2 cells from the basal side and localizes in distinct vesic les above the nucleus. The sensitivity of apotransferrin in stimulatin g Fe transport suggests a unique interaction of apotransferrin with th e basal surface of the intestinal epithelium. (C) 1998 by The American Society of Hematology.