title: The role of system A for neutral amino acid transport in the regulation of cell volume.
abstract: System A is a secondary active, sodium dependent transport system for neutral amino acids. Strictly coupled with Na,K-ATPase, its activity determines the size of the intracellular amino acid pool, through a complex network of metabolic reaction and exchange fluxes. Many hormones and drugs affect system A activity in specific cell models or tissues. In all the cell models tested thus far the activity of the system is stimulated by amino acid starvation, cell cycle progression, and the incubation under hypertonic conditions. These three conditions produce marked alterations of cell volume. The stimulation of system A activity plays an important role in cell volume restoration, through an expansion of the intracellular amino acid pool. Under normal conditions, system A substrates represent a major fraction of cell compatible osmolytes, organic compounds that exert a protein stabilizing effect. It is, therefore, likely that the activation of system A represents a portion of a more complex response triggered by exposure to stresses of various nature. Since system A transporters have been recently cloned, the molecular bases of these regulatory mechanisms will probably be elucidated in a short time.
authors.affiliation: Department of Experimental Medicine, University of Parma, Italy. ovidio.bussolati@unipr.it
authors.forename: O
authors.initials: O
authors.lastname: Bussolati
authors.forename: V
authors.initials: V
authors.lastname: Dall'Asta
authors.forename: R
authors.initials: R
authors.lastname: Franchi-Gazzola
authors.forename: R
authors.initials: R
authors.lastname: Sala
authors.forename: B M
authors.initials: BM
authors.lastname: Rotoli
authors.forename: R
authors.initials: R
authors.lastname: Visigalli
authors.forename: J
authors.initials: J
authors.lastname: Casado
authors.forename: M
authors.initials: M
authors.lastname: Lopez-Fontanals
authors.forename: M
authors.initials: M
authors.lastname: Pastor-Anglada
authors.forename: G C
authors.initials: GC
authors.lastname: Gazzola
mesh_terms: D026905:Amino Acid Transport Systems / Q000737:chemistry* / Q000378:metabolism; D000596:Amino Acids / Q000378:metabolism*; D000818:Animals; D001692:Biological Transport; D002462:Cell Membrane / Q000378:metabolism; D006801:Humans; D007700:Kinetics; D008954:Models, Biological; D009995:Osmosis; D011485:Protein Binding; D020033:Protein Isoforms; D012964:Sodium / Q000378:metabolism; D000254:Sodium-Potassium-Exchanging ATPase / Q000378:metabolism
chemical_list: D026905:Amino Acid Transport Systems; D000596:Amino Acids; D020033:Protein Isoforms; D012964:Sodium; D000254:Sodium-Potassium-Exchanging ATPase