Transferrin and iron uptake by rat hepatocytes in culture.

Hepatic iron and transferrin metabolism was studied using rat transferrin doubly labeled with 59Fe and 125I and adult rat hepatocytes in primary monolayer culture. Iron uptake was linear for 48 h while transferrin uptake was biphasic. Total transferrin and iron uptake increased in a linear manner as the transferrin concentration was raised up to at least 130 microM. This indicates that transferrin and iron are taken up primarily by nonspecific processes, possibly by endocytosis (absorptive or fluid) and by the action of iron chelators. However, some evidence indicated the presence of receptors for diferric transferrin on hepatocytes: the molar ratio of iron to transferrin accumulation increased with incubation time, transferrin and iron uptake was proportional to the iron saturation of the transferrin, apotransferrin displaced bound apotransferrin but had no effect on the binding of diferric transferrin, and the molar ratio of iron to transferrin uptake decreased with increasing transferrin concentrations.