Osmoregulation of Neutral Amino Acid Transport

Abstract

Neutral amino acids are important organic osmolytes found in most osmotically stressed cells. During prolonged hypertonic stress, accumulation of neutral amino acids contributes to the cell volume recovery and may protect cellular proteins against salt denaturation. Hypertonicity activates system A transport, a major neutral amino acid transporter in mammalian cells, by a microtubule-dependent mechanism. Similar to the regulation of amino acid efflux induced by hypotonic-swelling, influx via system A may be under the control of intracellular ionic strength. An osmotically sensitive repressor may negatively regulate the gene expression of a regulatory protein which activates the preexisting system A transporter protein. Hypertonically activated protein kinases may be involved in this osmoregulation of amino acid transport.

Cytoskeletal-dependent activation of system A for neutral amino acid transport in osmotically stressed mammalian cells: A role for system A in the intracellular accumulation of osmolytes

“…The osmolarity of explained on the basis of a hypothetical model of regulation which has recently been reviewed (McGivan and the medium was increased from 280 mOsM to 480 mOsM by adding sucrose, as previously reported (Ruiz-Pastor- Pastor-Anglada et al, 1996) and supported by other laboratories (Dall'Asta et al, 1996a,b;. This exerts nearly maximal responses in system A activation in both NBL-1 and Chen and Kempson, 1995a).…”

“…Amino acid star-(mostly aminotransferases). Nevertheless, another funcvation increases system A transport activity (Gazzola tion for the accumulation of amino acids in mammalian et Moffett and Englesberg, 1984;Bracy et al, cells has recently been proposed (McGivan and Pastor-1986), probably by keeping in an inactive conformation Chen and Kempson, 1995a; Dall'Asta et a putative repressor protein that becomes an active al., 1996a,b;Pastor-Anglada et al, 1996, for review). repressor when the intracellular concentration of Neutral amino acids, mostly system A substrates, may amino acids increases Englesberg, 1984, 1986;Englesberg and Moffett, 1986).…”

Effects of arginine, L-alanyl-L-glutamine or taurine on neutrophil (PMN) free amino acid profiles and immune functions in vitro

“…This effect has been described in various other cell types as well (Lin et al, 1988). Alterations in PMN intracellular neutral amino acid concentrations, which were also connected with taurine incubation, may draw attention to its role as an important intracellular osmoregulator (Chen and Kempson, 1995). As expected, increases in intracellular taurine levels decreased intracellular neutral amino acid profiles which may impart osmoprotection to PMN-cells (Horio et al, 1997;Fugelli et al, 1995).…”

Effects of osmoprotectant compounds on NCAM polysialylation under hyperosmotic stress and elevated pCO2

“…Increased intracellular [Na + ] ([Na + ] i ) has been found to decrease the catalytic rates and increase the K m values of several enzymes, including tuna lactate dehydrogenase and crab pyruvate kinase (Yancey et al, 1982). The addition of osmoprotective compounds, including organic methylamines such as glycine betaine, reduces K m and thermodynamically stabilizes macromolecules (reviewed by Chen and Kempson, 1995). Thus, it is possible that elevated [Na + ] i could reduce the polysialyltransferase activity and, hence, decrease the NCAM PSA content.…”