Inhibition of nitrobenzylthioinosine-sensitive adenosine transport by elevated D-glucose involves activation of P2Y2 purinoceptors in human umbilical vein endothelial cells.

Chronic incubation with elevated D-glucose reduces adenosine transport in endothelial cells. In this study, exposure of human umbilical vein endothelial cells to 25 mmol/L D-glucose or 100 micromol/L ATP, ATP-gamma-S, or UTP, but not ADP or alpha,beta-methylene ATP, reduced adenosine transport with no change in transport affinity. Inhibition of transport by D-glucose, ATP, and ATP-gamma-S was associated with reduced maximal binding, with no changes in the apparent dissociation constant for nitrobenzylthioinosine (NBMPR). A significant reduction (approximately 60+/-10%, P<0.05; n=6) in the number of human equilibrative NBMPR-sensitive nucleoside transporters (hENT1s) per cell (1.8+/-0.1x10(6) in 5 mmol/L D-glucose) and in hENT1 mRNA levels was observed in cells exposed to D-glucose or ATP-gamma-S. Incubation with elevated D-glucose, but not with D-mannitol, increased the ATP release by 3+/-0.2-fold. The effects of D-glucose and nucleotides on the number and activity of hENT1 and hENT1 mRNA were blocked by reactive blue 2 (nonspecific P2Y purinoceptor antagonist), suramin (Galpha(s) protein inhibitor), or hexokinase but not by pyridoxal phosphate-6-azophenyl-2',4'-disulfonic acid (nonselective P2 purinoceptor antagonist). Our findings demonstrate that inhibition of adenosine transport via hENT1 in endothelial cells cultured in 25 mmol/L D-glucose could be due to stimulation of P2Y2 purinoceptors by ATP, which is released from these cells in response to D-glucose. This could be a mechanism to explain in part the vasodilatation observed in the early stages of diabetes mellitus or in response to D-glucose infusion.