Glutamate transport by Rcho-1 cells derived from rat placenta

Marginal giant cells within the rodent placenta are important sources of androgens, critical to maintenance of pregnancy. Androgen synthesis requires NADPH, a by-product of glutamate oxidation. We examined the uptake of glutamate into rat choriocarcinoma cells, which have been shown to maintain many of the characteristics of marginal giant cells in culture. Na⁺-dependent, D-aspartate inhibitable uptake consistent with System X_AG^- mediated transport was present, as were proteins capable of System X_AG^- activity, EAAC1, GLAST1, and GLT1. Glutamate uptake in rat choriocarcinoma cells was up-regulated by amino acid deprivation - a response that was not reversed by the addition of glutamate to the media. Inhibition data suggested upregulation of transport activity mediated by either EAAC1 or GLAST1 at 6 h, whereas at 24 and 48 h, up-regulation of GLT1 plays an increasing role. Levels of EAAC1 immunoreactive protein increased with time under amino acid depleted conditions, whereas those of GLAST1 and GLT1 remained stable or declined but not significantly.