Sodium-dependent amino acid/proton antiporter. Mediates electrogenic cotransport of glutamine and sodium ions in exchange for protons. Also recognizes histidine and asparagine. May mediate amino acid transport in either direction under physiological conditions. May play a role in nitrogen metabolism and synaptic transmission. Expressed in skeletal muscle, liver, kidney, heart and brain. Not detected in gut, lung or spleen. Expressed ubiquitously in hepatocytes in liver whereas in kidney expression is restricted to the medulla. Within brain, expressed in glial cells. In the cerebellum, expressed on Bergmann glial fibers in the molecular layer and astrocytes in the granule layer. Belongs to the amino acid/polyamine transporter 2 family.