Water channel proteins AQP3 and AQP9 are present in syncytiotrophoblast of human term placenta.

The syncytiotrophoblast of human term placenta (HST) is a continuous, multinucleated structure with minimal tight junctions, which results from the fusion of the underlying cytotrophoblast cells. Consequently, the transport of metabolites, ions and water from mother to fetus could take place primarily via transcellular routes. Transcellular water flux may be facilitated by aquaporins, membrane proteins functioning as water channels that are widely expressed in cells and tissues. Here, we report the presence of AQP3 and AQP9 in the apical membranes of HST using RT-PCR, immunoblotting and immunohistochemistry. Since AQP3 is not only a water channels, but also permits the rapid passage of both urea and glycerol, while AQP9 also mediates the passage of carbamides, polyols, purines, and pyrimidines, we have speculated that these proteins could be involved in the transport of water and solutes from mother to fetus.