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Pharm Res. 2002 Feb;19(2):154-61.

Proton gradient-dependent transport of valproic acid in human placental brush-border membrane vesicles.

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Department of Medico-Pharmaceutical Sciences, Graduate School of Pharmaceutical Sciences, Kyushu University, Fukuoka, Japan.



To investigate the transport mechanism of valproic acid across the human placenta, we used human placental brush-border membrane vesicles and compared them with that of lactic acid.


Transport of [3H]valproic acid and [14C]lactic acid was measured by using human placental brush-border membrane vesicles.


The uptakes of [3H]valproic acid and [14C]lactic acid into brush-border membrane vesicles were greatly stimulated at acidic extravesicular pH. The uptakes of [3H]valproic acid and [14C]lactic acid were inhibited by various fatty acids, p-chloromercuribenzene sulfonate, alpha-cyano-4-hydroxycinnamate, and FCCP. A kinetic analysis showed that it was saturable, with Michaelis constants (Kt) of 1.04 +/- 0.41 mM and 1.71 +/- 0.33 mM for [3H]valproic acid and [14C]lactic acid, respectively. Furthermore, lactic acid competitively inhibited [3H]valproic acid uptake and vice versa.


These results suggest that the transport of valproic acid across the microvillous membrane of human placenta is mediated by a proton-linked transport system that also transports lactic acid. However, some inhibitors differentially inhibited the uptakes of [3H]valproic acid and [14C]lactic acid, suggesting that other transport systems may also contribute to the elevated fetal blood concentration of valproic acid in gravida.

[Indexed for MEDLINE]

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