Identification of a sorbitol permease in human erythrocytes.
Sorbitol, a polyol derived from glucose by the enzyme, aldose reductase, is a common organic solute in many cells. It plays a role in the osmotic regulation of epithelial cells and in the pathology of uncontrolled diabetes. To learn more about sorbitol transport, we measured D-[14C]sorbitol influx in human erythrocytes. Sorbitol influx at 37 degrees 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/mol, and the Q10 over the range 10-50 degrees C was 1.8, higher than predicted for diffusion through an aqueous pore. Glucose transport inhibitors either had no effect (1 mM phloridzin) or minimally inhibited (approximately 35% inhibition by 10 microM cytochalasin B or 250 microM phloretin) sorbitol influx. Influx was stimulated twofold by 0.5 mM p-chloromercuribenzoic acid, an inhibitor of glucose transport, and this was reversed by 2 mM dithiothreitol. Sorbitol influx was neither Na dependent nor sensitive to changes in cell volume. Glucose, fructose, mannitol, 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.
Kracke
G R
GR
Department of Anesthesiology, University of Missouri School of Medicine, Columbia 65212.
Preston
G G
GG
Stanley
T H
TH
D000818:Animals; D002241:Carbohydrates / Q000037:antagonists & inhibitors; D002463:Cell Membrane Permeability; D004285:Dogs; D004912:Erythrocytes / Q000201:enzymology*; D006801:Humans; D026901:Membrane Transport Proteins / Q000097:blood*; D009994:Osmolar Concentration; D009995:Osmosis; D011817:Rabbits; D012756:Sheep; D012964:Sodium / Q000494:pharmacology; D013012:Sorbitol / Q000378:metabolism* / Q000493:pharmacokinetics; D013438:Sulfhydryl Compounds / Q000494:pharmacology; D013696:Temperature; D013997:Time Factors
D002241:Carbohydrates; D026901:Membrane Transport Proteins; D013438:Sulfhydryl Compounds; D013012:Sorbitol; C086478:sorbitol permease; D012964:Sodium