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American journal of physiology. Renal physiology, 1995-06, Vol.268 (6), p.983-F996
Ort / Verlag
United States
Erscheinungsjahr
1995
Link zum Volltext
Quelle
MEDLINE
Beschreibungen/Notizen
M. B. Burg
National Heart, Lung, and Blood Institute, Bethesda, Maryland 20892-1598, USA.
Cells almost universally respond to the stress of long-term hyperosmolality
by accumulating compatible organic osmolytes. This allows them to maintain
normal cell volume without a deleterious increase in intracellular
inorganic ion concentration. Cells in the renal inner medulla are exposed
to variable concentrations of salt and urea that may reach molal levels.
The organic osmolytes that they accumulate include sorbitol, betaine,
inositol, taurine, and glycerophosphocholine (GPC). This review considers
recent advances in understanding osmotic regulation of these substances.
Sorbitol is synthesized from glucose catalyzed by aldose reductase.
Hypertonicity elevates the abundance of this enzyme by increasing
transcription of its gene. Betaine is taken up via a specialized
transporter. Hypertonicity raises the number of transporters by increasing
their transcription. Current studies demonstrate that the 5' regions
flanking the aldose reductase and betaine transporter genes contain osmotic
response elements that increase transcription in response to hypertonicity.
Osmotic regulation of inositol and taurine uptake also involves increased
expression of specific transporter genes. GPC is unique in that its level
rises in response to high urea, as well as hypertonicity. GPC accumulation
is mainly regulated by changes in its degradation to choline, catalyzed by
GPC:choline phosphodiesterase. Numerous other genes, including those for
heat shock proteins, are also induced by hypertonicity. Their regulation
and their role in osmotic regulation are the subject of considerable
ongoing research.