Basic amino acid transport in renal papilla: microinfusion of Henle's loops and vasa recta

To determine whether basic amino acids, like acidic and neutral amino acids, could be reabsorbed distal to tips of Henle's loops and recycled between loops and vasa recta in the renal papilla, we continuously microinfused ascending Henle's loops and vasa recta with 14C-labeled L-lysine (L-Lys; 1.28 mM) or L-arginine (L-Arg; 1.17 mM) and 3H-labeled inulin. We also determined percent of recovered radiolabel as intact amino acid. Like acidic and neutral amino acids, relative to inulin, approximately 30% of L-Lys and approximately 45% of L-Arg microinfused into Henle's loops were reabsorbed. However, whereas radiolabeled L-Lys reabsorption, like reabsorption of acidic and neutral amino acids, was not readily inhibited, radiolabeled L-Arg reabsorption was reduced to approximately 25% by addition of unlabled L-Arg (50 mM) or L-homoarginine (L-Homo-Arg) (50 mM) to infusate. This observation provides greater evidence for specific, carrier-mediated reabsorption for L-Arg than for acidic or neutral amino acids. About 36% (relative to inulin) of each of these amino acids microinfused into ascending vasa recta apparently was transferred directly into ipsilateral tubular structures (probably thin descending limbs of Henle's loops). Transfer of radiolabeled L-Arg was reduced to approximately 8% by the inclusion of unlabeled L-Arg (50 mM) in infusate. Transfer of unlabeled L-Lys was unaffected by inclusion of unlabeled L-Lys (50 mM) in infusate but was reduced to approximately 20% by inclusion of unlabeled L-Arg (50 mM) or L-Homo-Arg (50 mM) in infusate. (ABSTRACT TRUNCATED AT 250 WORDS)