Accumulation and release of iron in polarly and non-polarly cultured trophoblast cells isolated from human term placentas

We investigated the usefulness of membrane grown human term trophoblast cel ls in transferrin-mediated iron transfer studies. We showed that diferric t ransferrin is taken up both at the microvillous and at the basal membrane b y means of receptor-mediated endocytosis. Uptake from the microvillous side is predominant. This corresponded with a much higher expression of transfe rrin receptors at the microvillous membrane as compared to the basal one. I ron appeared to accumulate in the cell. Accumulation was higher when transf errin was supplied at the microvillous side. Transfer of iron could not be assessed because uptake of transferrin by the cells was much less than pass ive diffusion of transferrin through the cell-free filter. The observation of iron accumulation was unexpected for a transfer epithelium. Could it be that part of the iron taken up by the cells is rapidly released whereas the remaining part accumulates? In this case the rate of iron uptake should be higher than the rate of iron accumulation. This question was assessed with non-polarly cultured trophoblast cells. We showed that like in polar cells iron accumulated in ferritin. A new experimental design enabled us to demo nstrate that indeed the rate of transferrin-mediated iron is in excess over iron accumulation. We thus provide evidence for a mechanism that enables r apid transfer of iron across the syncytiotrophoblast cell layer. (C) 1999 E lsevier Science Ireland Ltd. All rights reserved.