The bovine renal epithelial cell line NBL-1 expresses a broad specificity Na(+)-dependent neutral amino acid transport system (System Bo) similar to that in bovine renal brush border membrane vesicles.

(1) In the bovine renal epithelial cell line NBL-1, transport of alanine and glutamine is highly Na(+)-dependent while the transport of leucine and phenylalanine is also stimulated by Na+ although to a much lesser extent. (2) Na(+)-dependent alanine transport is insensitive to inhibition by methyl AIB, lysine and glutamate but is inhibited by a range of other neutral amino acids. (3) Inhibition of Na(+)-dependent alanine transport by glutamine, phenylalanine and leucine is competitive indicating that these amino acids are transported on a common carrier. (4) Amino acid transport in these cells appears to be localised preferentially on the basolateral membrane. (5) The results are consistent with the presence in confluent cells of a broad-specificity Na(+)-dependent neutral amino acid transport system (System Bo) similar to that in bovine BBMV. An Na(+)-independent system with high activity similar to System L is also present. (6) It is argued that previous results in the literature are consistent with the occurrence of this broad-specificity system in other renal cell lines.