OSMOREGULATION OF NA+-INOSITOL COTRANSPORTER ACTIVITY AND MESSENGER-RNA LEVELS IN BRAIN GLIAL-CELLS
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- OSMOREGULATION OF NA+-INOSITOL COTRANSPORTER ACTIVITY AND MESSENGER-RNA LEVELS IN BRAIN GLIAL-CELLS
- PAREDES, A; MCMANUS, M; Kwon, H. Moo; STRANGE, K
- Issue Date
- American Physiological Society
- AMERICAN JOURNAL OF PHYSIOLOGY, v.263, no.6, pp.C1282 - C1288
- 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 K(m). 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.
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