The cells of the renal papilla are subject to widely varying extracellular osmolalities. In antidiuresis these cells are surrounded by hypertonic fluids, while in diuresis interstitial solute concentrations decline to levels comparable to those of the renal cortex. Papillary cells adapt to these extreme variations in extracellular tonicity by modulating the intracellular concentrations of small organic osmoeffectors (osmolytes), such as trimethylamines (glycerophosphorylcholine, betaine) and polyols (sorbitol, inositol). Variations in the intracellular concentrations of these osmolytes are accomplished by transmembrane net movement of water (cell swelling or shrinkage), by regulation of release and/or uptake of osmoeffectors via specific transmembrane transport pathways, and by changes in the intracellular synthesis of these organic compounds. These adaptive mechanisms allow intracellular electrolyte concentrations to remain relatively constant, despite extreme fluctuations in extracellular salinities. Accumulation of nonperturbing, organic osmolytes rather than inorganic electrolytes at high extracellular tonicities avoids the deleterious effects of elevated electrolyte concentrations on intracellular macromolecules. In addition, some of these osmolytes (trimethylamines) are assumed to counteract the adverse effects of high urea concentrations on the structure and function of cell proteins.
KeywordsUrea Shrinkage Proline Fructose Choline
Unable to display preview. Download preview PDF.
- 8.Schimassek H, Kohl D, Bücher T (1959) Glycerylphosphorylcholine, die Nierensubstanz “Ma-Mark” von Ullrich. Biochem Z 331: 87–97Google Scholar
- 10.Wirthensohn G, Lefrank S, Guder WG, Beck FX (1987) Studies on the role of glycerophosphorylcholine and sorbitol in renal osmoregulation. In: Kovacevic Z, Guder WG (eds) Molecular nephrology: biochemical aspects of kidney function. Walter de Gruyter, Berlin, pp 321–327Google Scholar
- 13.Beck FX, Dörge A, Thurau K, Guder WG (1990) Cell osmoregulation in the countercurrent system of the renal medulla: The role of organic osmolytes. In: Beyenbach KW (ed) Cell volume regulation, comp physiol. Karger, Basel, pp 132–158Google Scholar
- 17.Yancey PH (1988) Osmotic effectors in kidneys of xeric and mesic rodents: corticomedullary distributions and changes with water availability. J Comp Physiol 158: 369–380Google Scholar
- 21.Chambers ST, Kunin CM (1987) Osmoprotective activity for Escherichia coli in mammalian renal inner medulla and urine. Correlation of glycine and proline betaines and sorbitol with response to osmotic loads. J Clin Invest 80: 1255–1260Google Scholar
- 23.Guder WG, Beck FX, Schmolke M (1991) Organic compounds in renal volume regulation. Proceedings of the XIth Congress of nephrology, July 15–20 1990. Springer, Tokyo Berl in Heidelberg.Google Scholar
- 27.Schmolke M, Bornemann A, Guder WG (to be published) Distribution and regulation of organic osmolytes along the nephron. In: Koide H, Endou H, Kurokawa K (eds) Cell biology of nephron heterogeneity: fine structure and functions. Karger, BaselGoogle Scholar
- 29.Eng J, Berkowitz BA, Balaban RS (to be published) Renal distribution and metabolism of [2H9]choline. A2H NMR and MRI study. NMR BiomedGoogle Scholar
- 42.Bevan C, Theiss C, Kinne RKH (1990) Role of Car` in sorbitol release from rat inner medullary collecting duct ( IMCD) cells under hypoosmotic stress. Biochem Biophys Res Comm 170: 563–568Google Scholar