Selectivity properties of a Na-dependent amino acid cotransport system in adult alveolar epithelial cells
American Journal of Physiology - Lung cellular and Molecular Physiology
Selectivity properties of a Na-dependent amino acid cotransport system in adult alveolar epithelial cells. Am J Physiol Lung Cell Mol Physiol 279: L911-L915, 2000.-We investigated the amino acid specificity of a Na-dependent amino acid cotransport system that contributes to transepithelial Na absorption in the apical membrane of cultured adult rat alveolar epithelial cell monolayers. Short-circuit current was increased by basic, uncharged polar, and nonpolar amino acids but not by L-aspartic
... ot by L-aspartic acid or L-proline. EC 50 values for L-lysine and L-histidine were 0.16 and 0.058 mM, respectively. The L-lysine-stimulated short-circuit current was Na dependent, with a concentration causing a half-maximal stimulation by Na of 44.24 mM. L-Serine, L-glutamine, and L-cysteine had EC 50 values of 0.095, 0.25, and 0.12 mM, respectively. L-Alanine had the highest affinity, with an EC 50 of 0.027 mM. We conclude that monolayer cultures of adult rat alveolar epithelial cells possess a broad-specificity Nadependent amino acid cotransport system with properties consistent with system B 0,ϩ . We suggest that this cotransport system plays a critical role in recycling of constituent amino acids that make up glutathione, thus ensuring efficient replenishment of this important antioxidant within the alveolar fluid.