Characterization of l-arginine transporters in rat renal inner medullary collecting duct

Abstract

Previous work from our laboratory has demonstrated that the inner medullary collecting duct (IMCD) expresses a large amount of nitric oxide synthase (NOS) activity. The present study was designed to characterize the transport of NOS substrate,l-arginine, in a suspension of bulk-isolated IMCD cells from the Sprague-Dawley rat kidney. Biochemical transport studies demonstrated an l-arginine transport system in IMCD cells that was saturable and Na+ independent ( n = 6).l-Arginine uptake by IMCD cells was inhibited by the cationic amino acids l-lysine, l-homoarginine, and l-ornithine (10 mmol/l each) and unaffected by the neutral amino acids l-leucine, l-serine, andl-glutamine. Both l-ornithine ( n = 6) and l-lysine ( n = 6) inhibited NOS enzymatic activity in a dose-dependent manner in IMCD cells, supporting the important role of l-arginine transport for NO production by this tubular segment. Furthermore, RT-PCR of microdissected IMCD confirmed the presence of cationic amino acid transporter CAT1 mRNA, whereas CAT2A, CAT2B, and CAT3 were not detected. These results indicate that l-arginine uptake by IMCD cells occurs via system y+, is encoded by CAT1, and may participate in the regulation of NO production in this renal segment.