SLC38A3 (SN1), associated with the plasma membrane, mediates the uptake of glutamine, histidine, and, with lower efficiency, alanine and asparagine. Uptake of one molecule of amino acid is coupled to the uptake of two sodium ions and the export of one H+. Northern blotting experiments indicate gene expression in liver and kidney, and at much lower levels in brain, lung, skeletal muscle, spleen, stomach, testis, kidney, and intestine (Fei et al. 2000; Nakanishi et al. 2001).