Transport of transferrin-bound iron into rat Sertoli cells and spermatids

Transferrin (Tf), a major secretory protein of Sertoli cells, may transport iron to spermatogenic cells. This was assessed by measuring the uptake of Fe from 59Fe-125I-labelled rat Tf by Sertoli cells and round spermatids in vitro. Uptake of Fe from labelled Tf by Sertoli cells after a 72-h pre-incubation period was linear for 20 h (approximately 18 pmol/10(6) cells/20 h), whereas the uptake of Fe from labelled Tf by round spermatids after a 16-h pre-incubation period reached a plateau by 2 h (approximately 5 pmol/10(6) cells/2 h). The corresponding net uptake of Tf by both cell types was less than 0.1 pmol. High speed supernatants prepared from Sertoli cells and spermatids labelled with 59Fe-125I-Tf were fractionated by gel permeation chromatography. Separate peaks of protein-bound 59Fe and 125I-Tf were observed. Protein bound 59Fe could be precipitated with an antiserum to rat ferritin. It is concluded that iron from exogenous Tf is transported into Sertoli cells and round spermatids in vitro, and is complexed to intracellular ferritin. However, the present results do not exclude the possibility that Sertoli cell Tf may serve purposes other than iron transport.