Characterization of neutral amino acid uptake by cultured epithelial cells from pig kidney.

Two transport systems for neutral amino acids have been characterised in LLC-PK, cells. The first, which transports alanine in a sodium-dependent manner, also mediates alanine exchange and is perferentially inhibited by serine, cysteine, and alpha-amino-n-butyric acid. This system resembles the ASC system in Ehrlich ascites and some other cell types. There is only a small contribution of other systems to alanine uptake. The second, which transports leucine with no requirement for sodium and mediates leucine exchange, is blocked by 2-aminonorbornane-2-carboxylic acid and hydrophobic amino acids. This system is similar to the L system described in other cell types. LLC-PK1 cells retain several other features implying renal proximal tubule origin; our results thus suggest that these transport systems may be involved in the reabsorption of neutral amino acids by the nephron in vivo.