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Journal of Experimental Biology, Vol 178, Issue 1 269-274, Copyright © 1993 by Company of Biologists
JOURNAL ARTICLES |
P. Canals, M. A. Gallardo and J. Sanchez
Fasting in mammals and other vertebrates induces an increase in the ability of liver to extract from blood gluconeogenic substrates, such as plasma amino acids, which can also be used as an energy source (Cowey et al. 1977; Newsholme and Leech, 1983). In mammalian hepatocytes, food deprivation induces the appearance of a high-affinity component for short-chain amino acid transport, with the properties of system A, while there are no changes in the activities of a low-affinity system (the ASC system), system L (Fehlmann et al. 1979) or glutamine uptake (Hayes and McGivan, 1982). 'A' is the abbreviation for a Na+-dependent carrier which has L-alanine and other short-chain neutral amino acids as preferred substrates. Its tolerance to N-methylated analogues differentiates it from the ASC system. 'L' is the abbreviation for a Na+-independent carrier which has L-leucine as preferred substrate. 'asc' is the abbreviation for a carrier similar to the 'ASC' carrier with respect to preferred substrates, but it is Na+-independent.