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Growth regulation and amino acid transport in epithelial cells: Influence of culture conditions and transformation on A, ASC, and l transport activities
Author(s) -
Boerner Paula,
Saier Milton H.
Publication year - 1982
Publication title -
journal of cellular physiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.529
H-Index - 174
eISSN - 1097-4652
pISSN - 0021-9541
DOI - 10.1002/jcp.1041130209
Subject(s) - amino acid , methionine , cell culture , biochemistry , glutamine , isobutyric acid , leucine , chemistry , cell growth , alanine , transport system , biology , genetics , transport engineering , engineering
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.