Characterization of sodium-dependent amino acid transport activity during liver regeneration.
Liver regeneration occurs after removal of or damage to a portion of the liver; it leads to restoration of the original liver mass. The activities of three sodium-dependent amino acid transporters--system A, system N and system ASC--were determined during a 5-day period of liver regeneration in the rat. Seventy-percent hepatectomy or laparotomy was performed in pairs of rats; these rats' livers were removed at different time points after surgery. Transport activity was determined through measurement of the Na(+)-dependent uptake of tritiated amino acids by isolated hepatic plasma membrane vesicles. System A activity, as measured by the Na(+)-dependent uptake of 2-aminoisobutyric acid, is increased in the regenerating liver 2 to 24 hr after surgery compared with that of controls. Kinetic analysis of 2-(methylamino)isobutyric acid uptake showed a 100% increase in the maximum velocity of system A transport in the hepatectomized animals with no change in the Michaelis constant, suggesting an increase in the number of system A transport proteins in the plasma membrane of regenerating liver. During liver regeneration, no changes were noted in the transport activities of system N and system ASC as measured by the uptake of glutamine and cysteine, respectively, in the presence of 2-(methylamino)isobutyric acid. Our work suggests that system A performs a unique role in the secondary active transport of its substrate neutral amino acids to meet the metabolic demands of regenerating liver.
Fowler
F C
FC
Department of Medicine, University of Florida, Gainesville 32610-0214.
Banks
R K
RK
Mailliard
M E
ME
D026905:Amino Acid Transport Systems; D000596:Amino Acids / Q000378:metabolism*; D000621:Aminoisobutyric Acids / Q000378:metabolism; D000818:Animals; D001693:Biological Transport, Active / Q000187:drug effects; D002352:Carrier Proteins / Q000378:metabolism; D002462:Cell Membrane / Q000378:metabolism; D003545:Cysteine / Q000378:metabolism; D005973:Glutamine / Q000378:metabolism; D006498:Hepatectomy; D007700:Kinetics; D008099:Liver / Q000378:metabolism / Q000648:ultrastructure; D008115:Liver Regeneration / Q000502:physiology*; D008297:Male; D051381:Rats; D017207:Rats, Sprague-Dawley; D012964:Sodium / Q000494:pharmacology*; D014316:Tritium
D026905:Amino Acid Transport Systems; D000596:Amino Acids; D000621:Aminoisobutyric Acids; D002352:Carrier Proteins; D005973:Glutamine; D014316:Tritium; C100049:2-aminoisobutyric acid; D012964:Sodium; D003545:Cysteine