Regulation of transferrin receptor expression and distribution in in vitro cultured human cytotrophoblasts.

During gestation the transplacental iron transport is very important to the fetus. Iron uptake by the placenta can be studied in cultured cytotrophoblasts. The influence of culture time and human differic transferrin on the number and distribution of transferrin receptors (TfRs) was investigated in human cytotrophoblasts. Cytotrophoblasts cultured for 2.5 h had few TfRs (0.28 pmol/mg protein). With time, total TfR amounts increase (4.14 pmol/mg protein at 70 h). They increase to a higher level in cells cultured in iron-poor medium, indicating that iron has an effect on the TfR synthesis/breakdown ratio. TfRs were distributed between two 'active' (located at the cell surface and intracellularly) and one 'inactive' (located intracellularly) receptor pools. TfR distribution among these pools was modulated by culture time and iron. Trophoblasts regulated iron uptake by variation of number of surface TfRs via changes in total TfRs and redistribution of TfRs among the receptor pools.