Upregulation of the heteromeric y+LAT2 transporter contributes to ammonia-induced increase of arginine uptake in rat cerebral cortical astrocytes

Increased l-Arg (Arg) uptake to astrocytes and neurons is thought to contribute to enhanced nitric oxide (NO) synthesis and oxidative/nitrosative stress associated with hyperammonemia (HA). Recently we had shown that HA increases the expression in the brain of y+LAT2, an isoform of the y+L heteromeric transporter which promotes [3H]Arg efflux form brain cells in the presence of l-glutamine (Gln) (Zielińska et al., 2011). In this study, we demonstrate that a significant proportion of [3H]Arg uptake to cultured cortical astrocytes is likewise mediated by system y+L, in addition to the uptake showing characteristics of systems y+, B0+ and b0+. However, stimulation of [3H]Arg uptake by treatment with 5 mM ammonium chloride (“ammonia”) for 48 h could be solely ascribed to the y+L-mediated component of the uptake. Ammonia treatment increased the expression of the brain specific y+L isoform, y+LAT2, both at the mRNA and protein level, and silencing of the Slc7a6 gene coding for y+LAT2 protein specifically reduced the ammonia-induced [3H]Arg uptake. This study suggests an important role of y+LAT2 in the modulation of NO synthesis in the ammonia-exposed astrocytes.

► y+L system mediates Arg uptake in cultured cortical astrocytes more actively than system y+.
► Treatment of astrocytes with ammonia specifically increases Arg uptake mediated by system y+L.
► Ammonia increases the expression and activity of the transporter y+LAT2 in astrocytes.
► Silencing of the Slc7a6 gene coding for y+LAT2 protein reduced the ammonia-induced Arg uptake.
► y+LAT2 increase of Arg uptake is implicated in activation of astrocytic NO synthesis by ammonia.