Different Influence of Intracellular Glutamine Depletion on Glutamate Uptake Mediated by Amino Acid Transport Systems; EAATs and X-c, in Placental (BeWo) Cells

Abstract

Glutamate transporters are responsible for active transport of glutamate over the cell membrane and play an important role in the glutamate-glutamine cycle. The purpose of the present study was to investigate the influence of intracellular glutamine depletion on glutamate uptake mediated by amino acid transport systems; EAATs and X-c in placental choriocarcinoma (BeWo) cells as a model of human trophoblasts. Intracellular glutamine was depleted by culturing the cells in regular medium without glutamine and by treating with an inhibitor of glutamine synthetase (methionine sulfoximine; MSX), for 16 hours. The uptake of glutamate was measured by the use of appropriate substrates and ionic conditions. When cultured in not only the absence of extracellular glutamine but also treatment with MSX, the differential uptake of glutamate depended on the glutamate transport systems. This study concluded that the depletion of intracellular glutamine decreased the activity of EAATs; as sodium-dependent manner and at the same time significantly enhanced the activity of X-c; as sodium-independent manner for glutamate transport in the BeWo cells. Thus, intracellular glutamine was obligatory for maintenance of optimal activity of system EAATs in
the BeWo cells. The depletion of intracellular glutamine caused stress to the cells and the stress leaded to the upregulation of system X-c activity