C. Rybakowski et al., THE TRANSPORT OF VITAMIN-C IN THE ISOLATED HUMAN NEAR-TERM PLACENTA, European journal of obstetrics, gynecology, and reproductive biology, 62(1), 1995, pp. 107-114
We investigated the specific uptake (reference: [H-3]-L-glucose) as a
measure of membrane transfer of [C-14]-labeled L-ascorbic acid (AA), L
-dehydroascorbic acid (DHA) and diketogulonic acid using the single in
jection, double tracer dilution method in the artificially perfused lo
be of the near-term human placenta. The uptake of DHA (40-60%) on both
the fetal and the maternal side was 3-6 times higher than the uptake
of AA, whereas an uptake of diketogulonic acid was not detected. AA tr
ansport was slightly higher on the maternal side. Uptake of DHA was su
ppressed by phloretin and cytocholasin B, whereas AA transfer was not
affected. Low sodium concentrations inhibited the uptake of DHA. D-glu
cose (>20 mmol/l) inhibited the DHA uptake, and DHA inhibited D-glucos
e uptake but not L-alanine uptake. The K-m value (self inhibition) for
DHA was 6-14 mmol/l. Vitamin C enters the trophoblast predominantly a
s L-dehydroascorbic acid. Its transfer through the microvillous and ba
sal membrane might use the glucose transporter, however, a specific so
dium-dependent pathway is not ruled out. Our transfer data suggest an
intracellular pool of vitamin C which fills up with increasing plasma
DHA-concentrations.