Cleal, J.K., Brownbill, P., Godfrey, K.M., Cameron, I.T., Sibley, C.P., Hanson, M.A. and Lewis, R.M.
Placental materno-fetal transfer of serine by amino acid exchangers
Placenta, 27, (9-10), . (doi:10.1016/j.placenta.2006.07.004).
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Objectives: The mechanisms mediating amino acid transport across the basal membrane
of the placental syncytiotrophoblast into the fetal circulation are not well understood.
Our previous data indicate that amino acid exchangers mediate serine transport into the
fetoplacental circulation in exchange for alanine but not for glutamate. This study characterises
amino acid stimulation of serine transfer into the fetoplacental circulation by
Methods: Human placentas (n = 4) 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 ?mol /1 L-serine & glycine, 0.6 ?mol /1 14Cserine
and 20 ?mol /1 3H-glycine. Amino acid [12.5 ?mol] boluses were administered to
the fetal side inflow perfusate. 14C-serine and 3H-glycine were measured in maternal and
fetal venous samples by dual label liquid scintillation counting. Data (mean ± SEM) were
expressed as area under the curve (AUC) and analysed by one way ANOVA.
Results: Fetal side boluses of serine leucine threonine tryptophan and glutamine all resulted
in increased serine release (AUC values 242 ± 34, 132 ± 33, 309 ± 69, 85 ± 21 and
216 ± 82 nmol respectively). Following a fetal side bolus of glutamate, BCH or lysine
there was no significant increase in transfer of serine. Glycine release was not significantly
altered following any of the boluses.
Conclusion: This study demonstrates that serine is transported into the fetoplacental circulation
by amino acid exchangers in response to a range of substrates, but not lysine or
BCH, substrates of systems y+L and L. This is consistent with serine transport by Systems
ASC and b0+ but not Systems y+L and L.
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