Proceedings of The Physiological Society
University of Cambridge (2008) Proc Physiol Soc 11, PC40
Placental materno-fetal transfer of amino acids by exchangers
J. K. Cleal1, K. M. Godfrey1, M. A. Hanson1, R. M. Lewis1
1. The University of Southampton, Southampton, United Kingdom.
Objectives: The mechanisms mediating amino acid transport across the basal membrane of placental syncytiotrophoblast and into the fetal circulation are not well understood. Our previous data indicate that amino acid exchangers mediate serine (ser) and leucine (leu) transport into the fetoplacental circulation in exchange for specific amino acids (Cleal JK et al., (2007) J Physiol 582, 871-882). This study characterises amino acid stimulation of alanine (ala), phenylalanine (phe), tyrosine (tyr), isoleucine (iso), lysine (lys), threonine (thr), and glutamine (gln) transfer into the fetoplacental circulation. Methods: Human placentas (n = 5 per amino acid) were collected within 30 minutes of delivery and an intact cotyledon was perfused with a modified Earl’s bicarbonate buffer. The maternal arterial circulation was perfused with 50 µmol/l of amino acid plus radio-labelled tracer amino acid and 1.8 mM creatinine to determine the rate of paracellular diffusion. Amino acid [12.5 µmol] boluses were administered to the fetal side inflow perfusate. 14C- and 3H-labelled amino acids were measured in maternal and fetal (indicating transport) venous samples by liquid scintillation counting. Data (mean ± SEM) were expressed as area under the curve and analysed by one-way ANOVA. Results: Following fetal arterial boluses of specific amino acids transfer of ala, phe, tyr, iso, lys, thr, and gln increased, indicating that transport by exchange was taking place (Table 1). Conclusion: This study demonstrates that in the perfused human placenta amino acids are transported into the fetal circulation by exchange mechanisms. The data indicates activity of the exchangers ASC, LAT1 and y+LAT between the placenta and fetal circulation. This provides an important mechanism by which maternal amino acids can be transported to the fetus and thus be available for fetal growth and development.
Where applicable, experiments conform with Society ethical requirements