Symporter that cotransports neutral amino acids and sodium ions from the extracellular to the intracellular side of the cell membrane (PubMed:11342143, PubMed:19015196, PubMed:33928121). The transport is electrogenic, pH dependent and partially tolerates substitution of Na(+) by Li(+) (PubMed:11414754). Preferentially transports smaller amino acids, such as glycine, L-alanine, L-serine, L-asparagine and L-threonine, followed by L-cysteine, L-histidine, L- proline and L-glutamine and L-methionine (PubMed:11414754, PubMed:33928121). {ECO:0000269|PubMed:11342143, ECO:0000269|PubMed:11414754, ECO:0000269|PubMed:19015196, ECO:0000269|PubMed:33928121}. This is the function of Ensembl gene identifier ENSG00000139209 (SLC38A4, solute carrier family 38 member 4).