Transferrin and Iron Uptake by Rabbit Bone Marrow Cells in Vitro

S ummary . The interaction between rabbit transferrin and rabbit bone marrow cells and reticulocytes was investigated using transferrin labelled with 125 I and 59 Fe. The pattern of transferrin and iron uptake by bone marrow was found to be similar to that by reticulocytes and occurred in four stages, viz (1) adsorption of transferrin, (2) progressive uptake of transferrin, (3) release of the iron to the cell, (4) release of transferrin from the cell. Total transferrin uptake per bone marrow erythroid precursor cell was eight times that per reticulocyte, while the rate of iron uptake was at least twice as great with marrow cells. Transferrin uptake and release and iron uptake were temperature dependent. Transferrin and iron uptake were inhibited by metabolic inhbitors, particularly those affecting oxidative metabolism. The activation energies for the association and dissociation reaction of transferrin and the activation energy for iron uptake by bone marrow cells were higher than those reported for reticulocytes. A further difference between the two cell types was that at a constant iron concentration, iron uptake by bone marrow cells decreased with decreasing degrees of transferrin saturation with iron. Small increases in transferrin uptake by bone marrow cells were also obtained with increasing transferrin saturation. The data support the view that both iron and transferrin uptake are dependent upon cellular metabolism.