Changes of transferrin-free iron uptake by bone marrow erythroblasts in strenuously exercised rats

The effects of strenuous exercise on transferrin-free iron (Fe II) uptake by bone marrow erythroblasts in rats were investigated. Female Sprague-Dawley rats were randomly assigned to one of six groups, three of which underwent 3, 6, or 12 months of strenuous exercise (swimming 2 hr/day, 5 days/week) or their corresponding three control groups. At the end of experiments, bone marrow erythroblasts were isolated for Fe II uptake assay in vitro. It was found that the amounts of iron uptake into cytosole and stroma of the cells of rats in the groups undergoing 3 and 12 months of exercise did not differ from those in their corresponding sedentary groups. In addition, analysis of nonspecific and specific Fe II uptake by cytosole and stroma did not display any significant difference between the exercise and corresponding sedentary groups. However, the amount of Fe II uptake into cytosole and stroma was significantly increased in rats that exercised for 6 months compared with the corresponding controls. Nonspecific iron uptake into stroma was significantly higher in the exercise group than in the sedentary group (0.120 ± 0.018 vs. 0.049 ± 0.006 pM/106 cells, P < 0.01). The Vmax of the specific iron uptake into stroma was significantly higher (0.326 ± 0.024 vs. 0.238 ± 0.037 pM/106 cells, P < 0.05) and the Km of iron uptake into cytosol lower (0.08 ± 0.01 vs. 0.21 ± 0.03 μM, P < 0.001) in the exercise groups than in the control groups. These results indicate that 6 months of strenuous exercise could significantly increase Fe II uptake by the cells, probably by affecting the number and/or affinity of the putative iron carrier and the permeability to iron of cell membrane. The increased ability of cell-free iron accumulation in exercise might be a self-protective mechanism for body cells from the free iron-induced free radical reaction in addition to providing more iron for cell heme synthesis.