THE MECHANISMS OF NONHEME IRON UPTAKE DETERMINED IN IEC-6 RAT INTESTINAL-CELLS

The mechanisms of iron absorption, which control total body iron store s, are not fully understood. We have defined an in vitro model using r at small intestinal cells (IEC-6) to study nutrient uptake by the inte stine and have characterized the mechanisms of nonheme iron uptake in this model. IEC-6 cells were grown to confluency, and then Fe-59 solut ions were layered on the cells, allowing iron uptake to occur through the apical surface. Iron uptake increased over time and comparable res ults were seen with either Fe-59(II) or Fe-59(III). Two types of Fe-59 (II) binding sites were detected, a high affinity site with a dissocia tion constant of 1 x 10(-8) mol/L and 5 x 10(5) sites per cell, and a lower affinity site with a dissociation constant of 2 x 10(-6) mol/L a nd 2.6 x 10(6) sites per cell. The Fe-59 uptake was inhibited by low t emperature, low and high pH, prior iron loading of the cells, high osm otic concentrations, and by N,N'-dicyclohexylcarbodiimide, tannic acid , bathophenanthroline and colchicine. Uptake was not inhibited by vinb lastine or verapamil. Transferrin mRNA was not detected in IEC-6 cells grown under normal growth conditions but could be induced under some other conditions. IEC-6 cell proteins that bind iron were detected in a subcellular vesicle fraction having estimated molecular weights of 1 20,000, 95,000, 55,000 and 35,000. These studies confirm iron uptake s tudies by other models and demonstrate that IEC-6 cells possess iron-b inding moieties, a regulated iron uptake process, and little or no tra nscription of the transferrin gene under normal growth conditions.