Osmotic regulation of sorbitol in the thick ascending limb of
henles loop (talh).
Eckstein, Angela, R. Willi Grunewald.
Sektion Nephrologie, Universit[umlaut]atsklinik Ulm, 89070 Ulm,
FRG
APStracts 2:0164F, 1995.
Organic osmolytes such as sorbitol, inositol, glycerophosphorylcholin
and betaine play an important role in the osmoregulation of inner
medullary cells of the kidney. The cells of the outer medulla are
also exposed to elevated NaCl- and urea-concentrations during
antidiuresis. Therfore, we investigated the mechanisms involved in
the regulation of outer medullary organic osmolytes, especially cell
sorbitol content of immortalised epithelial cells of the thick
ascending limb of Henle_s loop (TALH). In the cultured cell model,
600 mosmol/l medium (osmolarity adjusted by addition of 150 mM NaCl
or 300 mM sucrose) increases the intracellular sorbitol content
significantly as compared with 300 mosmol/l. The accumulation of
sorbitol appears to be due to an increase of aldose reductase
activity, which catalyzes sorbitol synthesis. Sorbitol degradation by
sorbitol dehydrogenase was not detectable under our experimental
conditions. Following a sudden decrease of the extracellular
osmolarity the sorbitol permeability of the cellular membrane
increases 7-fold within 10 minutes as compared to isoosmolar
conditions. These results indicate that sorbitol beside inositol
plays an important role in the osmoregulation of TALH cells. While
the short term regulation involves rapid changes in sorbitol membrane
permeability, the long term adaptation to low osmolarities is
regulated by intracellular sorbitol synthesis.
Received 8 September 1993; accepted in final form 9 August 1995.
APS Manuscript Number F321-3.
Article publication pending Am. J. Physiol. (Renal Fluid Electrolyte
Physiology).
ISSN 1080-4757 Copyright 1995 The American Physiological Society.
Published in APStracts on 31 October 95