Regional specificity of iron uptake by small intestinal brush-border membranes from normal and iron-deficient mice.

Fe(II)-ascorbate uptake by purified small intestinal brush-border membrane vesicles prepared from proximal and distal segments was studied in normal and iron-deficient mice. Iron was maintained in a reduced, soluble form by a 20-fold excess of ascorbate at a physiological pH of 7.2-7.4. In normal mice, iron uptake by proximal membrane vesicles was three- to fourfold greater (approximately 1,700 pmol/mg prot) than from distal segments (approximately 500 pmol/mg prot). In iron-deficient mice, uptake of Fe(II) was also greater in proximal membranes (approximately 3,200 pmol/mg prot) than uptake from distal segments (approximately 350 pmol/mg prot), and the regional difference was almost 10-fold, without any change in distal segmental iron uptake. These results are consistent with the pattern of intestinal iron absorption in iron-replete and iron-deficient animals and indicate that regulatory changes in proximal intestinal brush-border membranes may account for the increased iron absorption known to occur in iron deficiency.