Cellular osmoregulation in renal medulla.

Cells of the renal medulla adapt osmotically to varying external electrolyte concentrations mainly by changing the intracellular content of small organic osmoeffectors (osmolytes) such as sorbitol, inositol and trimethylamines. This implies that despite extreme variations in extracellular tonicity the intracellular concentrations of monovalent electrolytes are stabilized at levels optimal for enzyme function and cell metabolism. In contrast to inorganic electrolytes these organic osmolytes are metabolically neutral and thus do not affect cell metabolism. In addition, some of these organic osmoeffectors, the trimethylamine compounds, are known to counteract the deleterious effects of high urea concentrations (prevailing in antidiuresis) on structure and function of cell proteins.