Sorbitol transport in rat renal inner medullary interstitial cells

Sorbitol plays an important role in renal osmoregulation. In the rat renal inner medulla sorbitol synthesis and sorbitol degradation are located in different cell types. Whereas sorbitol synthesis can be detected in the inner medullary collecting duct cells, sorbitol degradation takes place in the interstitial cells. Therefore, one can speculate that the cooperation between epithelial and interstitial cells requires sorbitol transport into interstitial cells.

Our studies were performed with an interstitial cell line derived from the renal inner medulla of Wistar rats. These cells have typical characteristics of renal fibroblasts. In addition, they possess a high activity of sorbitol dehydrogenase as determined in vivo. Uptake was measured by liquid scintillation counting. For studies on sorbitol metabolism sorbitol concentration was measured photometrically.

The results show that sorbitol transport into interstitial cells occurs via a yet to be described transport system. No saturation of sorbitol transport could be found up to an extracellular sorbitol concentration of 80 mmol/L. The transport was neither sodium nor chloride dependent. Trans-stimulation increased the sorbitol uptake. Sorbitol uptake was less inhibited by cytochalasin B than 2-deoxy-D-glucose uptake. The transport showed a high affinity for sorbitol and only little inhibition of sorbitol uptake by substances with a similar structure was observed.

Our results show a new sorbitol transport system in renal inner medullary interstitial cells, which is rather different from the described sorbitol permease in renal epithelial cells and from glucose transporters of the GLUT- and SGLT-family.