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

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Abstract
Two transport systems for neutral amino acids have been characterised in LLC‐PK1 cells. The first, which transport alanine in a sodium‐dependent manner, also mediates alanine exchange and is preferentially inhibited by serine, cysteine, and α‐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.