IDENTIFICATION OF A SORBITOL PERMEASE IN HUMAN ERYTHROCYTES

Sorbitol, a polyol derived from glucose by the enzyme, aldose reductas e, is a common organic solute in many cells. It plays a role in the os motic regulation of epithelial cells and in the pathology of uncontrol led diabetes. To learn more about sorbitol transport, we measured D-[C -14]sorbitol influx in human erythrocytes. Sorbitol influx at 37 degre es C was a linear function of sorbitol concentration over the range of 0.05-100 mM. The activation energy for sorbitol influx was 10.0 kcal/ mel, and the Q(10) over the range 10-50 degrees C was 1.8, higher tha n predicted for diffusion through an aqueous pore. Glucose transport i nhibitors either had no effect (1 mM phloridzin) or minimally inhibite d (similar to 35% inhibition by 10 mu M cytochalasin B or 250 mu M phl oretin) sorbitol influx. Influx was stimulated twofold by 0.5 mM p-chl oromercuribenzoic acid, an inhibitor of glucose transport, and this wa s reversed by 2 mM dithiothreitol. Sorbitol influx was neither Na depe ndent nor sensitive to changes in cell volume. Glucose, fructose, mann itol, myo-inositol, and gluconate, at four- to fivefold molar excesses over sorbitol, did not inhibit its influx. We conclude that there is a specific sorbitol transport pathway in human erythrocytes similar to the sorbitol permease in renal epithelial cells.