Growth regulation and amino acid transport in epithelial cells: Influence of culture conditions and transformation on A, ASC, and l transport activities

✍ Scribed by Paula Boerner; Milton H. Saier Jr.

• Publisher: John Wiley and Sons
• Year: 1982
• Tongue: English
• Weight: 967 KB
• Volume: 113
• Category: Article
• ISSN: 0021-9541
• DOI: 10.1002/jcp.1041130209

✦ Synopsis

Abstract

Amino acid transport in Madin‐Darby canine kidney (MDCK) cells, grown in a defined medium, was investigated as a function of cell density, exposure to specific growth factors, and transformation. MDCK cells were found to transport neutral amino acids by systems similar to the A, ASC, L, and N systems which have been characterized using other cell lines. Experimental conditions were developed for MDCK cells which allowed independent measurement of A, ASC, and L transport activities. The activity of the L system was measured as Na^+^‐independent leucine or methionine uptake at pH 7.4. The activity of the A system was measured as Na^+^‐dependent α(methylamino)isobutyric acid (mAIB) uptake at pH 7.4, the activity of the ASC system was measured as Na^+^‐dependent alanine uptake in the presence of 0.1 mM mAIB at pH 6.0, and the activity of system N was observed by measuring Na^+^‐dependent glutamine uptake at pH 7.4 in the presence of high concentrations of A and ASC system substrates. The L transport system responded minimally to changes in growth state, but Na^+^‐dependent amino add transport responded to regulation by growth factors, cell density, and transformation. The activities of the A and ASC systems both decreased at high cell density, but these activities responded dissimilarly under other conditions. The activity of the A system was stimulated by insulin, was inhibited by PGE~1~, and was elevated 3–7 fold in the transformed cell line, MDCK‐T~1~. The activity of the ASC system was slightly stimulated by insulin and by PGE~1~, but was unchanged after chemical transformation. Changes in cellular growth were monitored and were found to correlate best with the activity of the A system. These results suggested that MDCK cell growth may be more closely related to the activity of the A than of the ASC system.