Acute and chronic exposure of mouse cerebral microvessel endothelial cells to increased concentrations of glucose and galactose: effect on myo-inositol metabolism, PGE2 synthesis, and Na+/K(+)-ATPase transport activity.

Cultured mouse cerebral microvessel endothelial cells have a large intracellular myo-inositol content and rapidly take up extracellular myo-inositol. Myo-inositol uptake occurs by a high- and low-affinity transport system. Both transport systems appear to be Na(+)-dependent. The high- and low-affinity transport systems have a Km of 11 and 198 mumol/L and a Vmax of 47 and 381 pmol/min/mg protein, respectively. Acute exposure of cultured cells to 30 mmol/L D-glucose or D-galactose causes a decrease in myo-inositol uptake. The acute effect of glucose and galactose on myo-inositol uptake is sensitive to the extracellular myo-inositol concentration. The acute effect of glucose is apparently due to a competitive inhibition of high-affinity myo-inositol transport and has a Ki of 21 mmol/L. L-Glucose is more effective than D-glucose in decreasing myo-inositol uptake. In contrast, 2-deoxyglucose or 3-0-methylglucose does not acutely inhibit myo-inositol uptake. This suggests that the hydroxyl groups on carbons 2 and 3 of glucose are necessary for inhibitory activity. Chronic exposure of cells to media containing 136.4 mumol/L myo-inositol and 30 mmol/L glucose has no effect on myo-inositol accumulation from the extracellular fluid, myo-inositol incorporation into inositol phospholipids, or total myo-inositol content. Chronic exposure of the cells to media containing 30 mmol/L glucose causes only a small increase in the intracellular sorbitol content. In contrast, chronic exposure of the cells to media containing 30 mmol/L galactose causes a large increase in galactitol content and a decrease in myo-inositol accumulation, myo-inositol incorporation into inositol phospholipids, and intracellular myo-inositol content. Sorbinil treatment of the galactose-supplemented media protects the cells form changes in myo-inositol metabolism and content. Chronic exposure of the cells to media containing 30 mmol/L glucose or 30 mmol/L galactose causes a decrease in ouabain-sensitive Na+/K(+)-ATPase transport activity, which is corrected by the addition of sorbinil to the media. Chronic exposure of the cells to media containing 45 mmol/L glucose, but not galactose, causes an increase in PGE2 production. These studies suggest that acute or chronic exposure of cultured microvessel endothelial cells to increased concentrations of glucose or galactose causes a decrease in myo-inositol uptake by different mechanisms. Chronic exposure of the cells to increased concentrations of glucose or galactose causes alterations in endothelial cell properties, including Na+/K(+)-ATPase transport activity and eicosanoid synthesis. The data are not clearly supportive of polyol accumulation and myo-inositol depletion as being responsible for the decrease in Na+/K+ pump activity.