title: Comparison of system N in fetal hepatocytes and in related cell lines.
abstract: In contrast to the changes seen in membrane transport systems for other neutral, anionic, and cationic amino acids, System N for glutamine, histidine, and asparagine in the rat hepatocytes shows nearly constant properties at the fetal, differentiated, and cultured hepatoma stages. These properties were tested by measuring the Na+-dependent transport of glutamine. This approximate constancy applies not only to the transport selectivity of the system among neutral amino acids, but also to its tolerance of Li+ as a substitute for Na+, its characteristic sensitivity to pH lowering, its relative sensitivity to N-ethylmaleimide, its stimulation by amino acid deprivation, and its failure to respond to insulin or glucagon. The properties of histidine as a substrate for System N were also examined. Inhibition studies with different cell types suggest that the Na+-dependent glutamine and histidine uptake is more restricted to System N in the hepatoma line H35 (H4-11-EC,3) and in the fetal hepatocyte than in hepatoma line HTC and the Ehrlich cells. The Na+-independent component of glutamine and histidine uptake was greater in the hepatoma cells in continuous culture than in fetal and adult hepatocytes in primary culture. Trans-stimulation of glutamine and histidine influx into H35 cells occurs predominantly by the Na+-independent route.
mesh_terms: D000375:Aging; D000596:Amino Acids / Q000378:metabolism*; D000621:Aminoisobutyric Acids / Q000494:pharmacology; D000818:Animals; D001216:Asparagine / Q000378:metabolism; D001692:Biological Transport / Q000187:drug effects; D002286:Carcinoma, Ehrlich Tumor / Q000378:metabolism; D006528:Carcinoma, Hepatocellular / Q000378:metabolism*; D002460:Cell Line; D005033:Ethylmaleimide / Q000494:pharmacology; D005973:Glutamine / Q000378:metabolism; D006639:Histidine / Q000378:metabolism; D006801:Humans; D006863:Hydrogen-Ion Concentration; D008094:Lithium / Q000494:pharmacology; D008099:Liver / Q000196:embryology* / Q000378:metabolism; D008113:Liver Neoplasms; D012964:Sodium / Q000494:pharmacology
chemical_list: D000596:Amino Acids; D000621:Aminoisobutyric Acids; D005973:Glutamine; C017911:2-(methylamino)isobutyric acid; D006639:Histidine; D001216:Asparagine; D008094:Lithium; D012964:Sodium; D005033:Ethylmaleimide