title: Osmoregulation of Na(+)-inositol cotransporter activity and mRNA levels in brain glial cells.
abstract: During plasma hypertonicity brain volume is regulated acutely by electrolyte uptake and chronically by accumulation of organic solutes such as inositol. Cultured rat C6 glioma cells, an astrocyte-like cell line, show a similar pattern of volume control. Volume regulatory accumulation of inositol requires external inositol, indicating that membrane transport plays a central role in this process. The inositol uptake pathway is Na+ dependent and exhibits Michaelis-Menten kinetics. Chronic hypertonic acclimation results in a twofold increase in the maximum velocity of the transporter without changing the Km. Hypertonic stress also results in a 17-fold increase in transporter mRNA. Elevation of mRNA levels precedes activation of the transporter by 4-6 h, suggesting that increased inositol uptake is mediated by synthesis and membrane insertion of new transport proteins. Reacclimation of hypertonic cells to isotonicity causes a rapid reduction of transporter mRNA levels to control levels within 4 h. In contrast, downregulation of transport activity does not begin until between 10 and 24 h after reexposure to isotonicity.
authors: Department of Medicine, Children's Hospital, Harvard Medical School, Boston, Massachusetts 02115.
authors: A
authors: A
authors: Paredes
authors: M
authors: M
authors: McManus
authors: H M
authors: HM
authors: Kwon
authors: K
authors: K
authors: Strange
mesh_terms: D000818:Animals; D001921:Brain / Q000166:cytology / Q000378:metabolism*; D002352:Carrier Proteins / Q000235:genetics / Q000378:metabolism*; D002478:Cells, Cultured; D003470:Culture Media; D006360:Heat-Shock Proteins / Q000235:genetics / Q000378:metabolism*; D006982:Hypertonic Solutions / Q000494:pharmacology; D007294:Inositol / Q000378:metabolism; D007552:Isotonic Solutions / Q000494:pharmacology; D008565:Membrane Proteins; D009457:Neuroglia / Q000378:metabolism*; D012333:RNA, Messenger / Q000378:metabolism*; D051381:Rats; D012964:Sodium / Q000502:physiology; D027981:Symporters; D014882:Water-Electrolyte Balance
chemical_list: D002352:Carrier Proteins; D003470:Culture Media; D006360:Heat-Shock Proteins; D006982:Hypertonic Solutions; D007552:Isotonic Solutions; D008565:Membrane Proteins; D012333:RNA, Messenger; D027981:Symporters; C073884:SLC5A3 protein, human; D007294:Inositol; D012964:Sodium