Functions as a sodium-dependent amino acid transporter. Mediates the saturable, pH-sensitive and electrogenic cotransport of glutamine and sodium ions with a stoichiometry of 1:1. May also transport small zwitterionic and aliphatic amino acids with a lower affinity. May supply glutamatergic and GABAergic neurons with glutamine which is required for the synthesis of the neurotransmitters glutamate and GABA. Inhibited by lithium, potassium, choline ions, N-methyl-D-glucamine and 2-methylamino-isobutyric acid (MeAIB). Restricted to the somatodendritic compartment of neurons. Found in the cellular processes of neurons in the developing brain. Specifically expressed in brain with the highest levels in cerebellum and thalamus (at protein level). Expressed in glutamatergic, GABAergic and a subset of dopaminergic neurons of the substantia nigra and cholinergic motoneurons (at protein level). Also expressed by ependymal cells lining the ventricle (at protein level). Expression is also detected in spinal cord, heart, colon and placenta. Expressed at all stages examined including E17, E19, P2, P10 and P14. Expressed in neocortex, hippocampus and neuroepithelium at E17 and more prominently expressed in striatum, hippocampus and cortex at postnatal days (at protein level). Up-regulated by forskolin in astrocytes. Belongs to the amino acid/polyamine transporter 2 family.