Cotransport systems in the brush border membrane of the human placenta.

The cotransport systems present in the brush border membrane of the human placental syncytiotrophoblast are reviewed. Attention is focused on the systems that are powered by the electrochemical gradient of Na+ (for example, for neutral amino acids but not for glucose), and on recently described systems in which K+ flux is coupled to C1- flux or to that for Na+ and C1-. These systems are similar to those found in other tissues and may be significant for net trans-placental transport and its control, as well as for the regulation of placental trophoblast volume.