IEC-6 cells are an appropriate model of intestinal iron absorption in rats

Regulation of iron absorption, which is the primary mechanism for maintaining body iron stores, occurs primarily in the proximal small intestine. Recent identification of proteins that are involved in iron absorption such as the uptake transporter-divalent metal transporter (DMT1), the basolateral transporter, IREG1, and the ferroxidase-hephaestin provide new opportunities to study this process. We evaluated the rat intestinal cell line, IEC-6, as a model of intestinal iron transport. This involved measuring the expression of DMT1 and IREG1 by Western blot analysis and confocal microscopy, and hephaestin by protein-dependent copper oxidase activity. DMT1 and IREG1 were expressed in IEC-6 cells. The uptake of 1 micromol/L ferrous iron [Fe(II)]:ascorbate and its efflux also was associated with the expression of DMT1 under different levels of iron loading. The expression of DMT1 changed inversely with iron levels as did the uptake of Fe(II). However, with different levels of cellular iron, IREG1 expression remained constant, as did the release of iron from the cells, suggesting that they could be related. Ceruloplasmin and apotransferrin did not enhance the rate or extent of iron release. Copper oxidase activity, considered to indicate hephaestin activity, was detected only intracellularly. Confocal microscopy showed DMT1 and IREG1 on the cell membrane of IEC-6 cells at 4 degrees C but at intracellular locations at 37 degrees C, indicating that these proteins can function at the cell membrane and intracellularly. In terms of iron absorption, IEC-6 cells have a villous enterocyte phenotype and are regulated by iron stores as occurs in vivo; therefore, they represent an appropriate cell model with which to study this process.