Differential responsiveness of cells of human amniotic epithelium to ferritin and 125I-prolactin in vitro.

Human amniotic epithelium has been found to consist of two cell types, known as dark and light cells, that are functionally different with respect to the passage of large molecules across the epithelium. Both cell types permit passage of ferritin intercellularly, whereas light cells incorporate this macromolecule. Dark cells impair the passage of 125I-PRL both inter- and intracellularly, whereas it is localized in light cells. In addition to a selectivity regarding the transmembrane passage of large molecules by the two cell types, we suggest that the osmoregulatory action of PRL on human amnion is restricted to the epithelial layer, and that its action may be mediated by light cells.