Figure 2.

Molecular transporter transcripts with confirmed syncytiotrophoblast location in the human placenta and their direction of transport. SLC (orange) and ABC (blue) are found in both apical (maternal-facing) and basolateral (fetal-facing) membranes. As seen by the schematic, understanding of complete transplacental routes for compound movement is incomplete. Grey dashed line indicates the transporter has been found to be expressed on both membranes. It is likely that many molecules must use a combination of transporters to cross the membrane and as many transporters have common substrates, this is entirely possible. Substrates mentioned here are generalized substrates of the superfamilies.