The release of iron by Sertoli cells in culture

In seminiferous tubules, iron transport from the blood to the abluminal germinal cells must occur through the Sertoli cell cytoplasm. We investigated the release of previously accumulated iron by cultured Sertoli cells. We found that Sertoli cells contain easily releasable and less easily releasable iron pools. Iron is released in a low molecular weight form (molecular weight less than 30,000). A high concentration of this low molecular weight iron in the medium reduces further iron release by Sertoli cells, whereas the addition of more medium or fresh medium increases further iron release. Apotransferrin stimulates the release of iron in a dose-dependent manner by chelating the low molecular weight iron. Rat and human apotransferrin are completely competitive in this respect. Diethylenetriamine penta acetic acid (DTPA), an extracellular iron chelator, and apotransferrin compete for iron binding and stimulation of iron release, indicating that no binding or uptake of the chelator by the cells is required. Desferrioxamine (DFO), an intracellular iron chelator, on the other hand, increases iron release more drastically, and apotransferrin cannot compete with it for iron. The addition of extracellular iron also increases the amount of 59Fe in the medium, probably by reducing the re-uptake of 59Fe. This is also demonstrated with primaquine, which blocks endocytosis and increases the amount of 59Fe in the medium. The presence of germinal cells also stimulates the release of iron by Sertoli cells. When cocultured, the germinal cells internalize iron as it is release by Sertoli cells.