Up-regulation of system A activity in the regenerating rat liver.
System A activity for neutral amino acid transport, measured as the MeAIB-sensitive Na(+)-dependent L-alanine uptake, is induced 6 h after partial hepatectomy in plasma membrane vesicles from rat livers. Other Na(+)-dependent transporters, like system ASC (MeAIB-insensitive Na(+)-dependent L-alanine transport) and the nucleoside carrier show similar inductions. Up-regulation of system A is not explained by changes in the dissipation rate of the Na+ transmembrane gradient, as deduced from uptake measurements performed in the presence of monensin. To determine whether induced system A shared any similarity with the activity found in hepatoma cell lines, we analyzed the N-ethylmaleimide (NEM) sensitivity of system A in both regenerating and control rat liver plasma membrane vesicles. NEM treatment was equally effective in inhibiting system A in both experimental groups. Thus, during the prereplicative phase of liver growth, a transport activity similar to basal system A is up-regulated in liver parenchymal cells, by a stable mechanism that does not involve changes in the Na+ transmembrane gradient.
Martínez-Mas
J V
JV
Departament de Bioquímica i Fisiologia, Universitat de Barcelona, Spain.
Ruiz-Montasell
B
B
Felipe
A
A
Casado
J
J
Pastor-Anglada
M
M
D000409:Alanine / Q000378:metabolism; D000596:Amino Acids / Q000378:metabolism*; D000818:Animals; D001692:Biological Transport / Q000187:drug effects; D005033:Ethylmaleimide / Q000494:pharmacology; D006498:Hepatectomy; D007700:Kinetics; D008115:Liver Regeneration / Q000502:physiology*; D008297:Male; D008985:Monensin / Q000494:pharmacology; D051381:Rats; D017208:Rats, Wistar; D012964:Sodium / Q000494:pharmacology; D015091:beta-Alanine / Q000031:analogs & derivatives / Q000494:pharmacology
D000596:Amino Acids; D015091:beta-Alanine; C012924:2,2-dimethyl-beta-alanine; D008985:Monensin; D012964:Sodium; D005033:Ethylmaleimide; D000409:Alanine