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

Abstract

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 5mM ammonium chloride (“ammonia”) for 48h 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.