High glucose concentrations inhibit glucose phosphorylation, but not glucose transport, in human endothelial cells

Glucose uptake is autoregulated in a variety of cell types and it is though t that glucose transport is the major step that is subjected to control by sugar availability. Here, we examined the effect of high glucose concentrat ions on the rate of glucose uptake by human ECV-304 umbilical vein-derived endothelial cells. A rise in the glucose concentration in the medium led a dose-dependent decrease in the rate of 2-deoxyglucose uptake. The effect of high glucose was independent of protein synthesis and the time-course anal ysis indicated that it was relatively slow. The effect was not due to inhib ition of glucose transport since neither the expression nor the subcellular distribution of the major glucose transporter GLUT1, nor the rate of 3-O-m cthylglucose uptake was affected. The total in vitro assayed hexokinase act ivity and the expression of hexokinase-I were similar in cells treated or n ot with high concentrations of glucose. In contrast, exposure of cells to a high glucose concentration caused a marked decrease in phosphorylated 2-de oxyglucose/free 2-deoxyglucose ratio. This suggests the existence of altera tions in the rate of in vivo glucose phosphorylation in response to high gl ucose. In summary, we conclude that ECV304 human endothelial cells reduce g lucose utilization in response to enhanced levels of glucose in the medium by inhibiting the rate of glucose phosphorylation, rather than by blocking glucose transport. This suggests a novel metabolic effect of high glucose o n cellular glucose utilization. (C) 1999 Elsevier Science B.V. All rights r eserved.