AJP - Cell Physiology, Vol 266, Issue 2 C343-C350, Copyright © 1994 by American Physiological Society
Identification of a sorbitol permease in human erythrocytes
G. R. Kracke, G. G. Preston and T. H. Stanley
Department of Anesthesiology, University of Missouri School of Medicine, Columbia 65212.
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.
