Differential effect of insulin and elevated glucose level on adenosine transport in rat B lymphocytes

Impaired lymphocyte function is a common feature of human diabetes. Nucleoside transport across the plasma membrane is an essential step during lymphocyte growth and activation. In our study, we evaluated the impact of diabetic conditions on nucleoside transport system in B lymphocytes. Examination of the nucleoside transporters expression level in B lymphocytes isolated from diabetic rats revealed significant changes in their mRNA levels. Experiments performed on B cells cultured in medium containing defined concentrations of glucose and insulin showed that the rENT1 mRNA level was sensitive to extracellular glucose concentration and was not affected by insulin. Increase of glucose concentration from 5 to 20 mM caused a decrease of rENT1 mRNA by 80% and was associated with decreased adenosine uptake by the B cells. The effect of glucose was blocked by PD98059, a MAPK kinase inhibitor. The mRNA levels of rENT2 and rCNT2 were highly dependent on insulin but not on glucose concentration. Exposure of lymphocytes to 10 nM insulin resulted in a 2-fold increase in rENT2 mRNA and a 50% decrease in the rCNT2 mRNA level. Alterations in mRNA levels of rENT2 and rCNT2 were associated with changes in adenosine transport. Insulin-induced changes in expression level of rENT2 were blocked by wortmannin, an inhibitor of phosphatidylinositide 3-kinase, whereas the effect of insulin on rCNT2 was inhibited by PD98059 and to a lesser extend by wortmannin. In summary, impaired nucleoside transport in diabetic B lymphocytes results from alterations in the expression of nucleoside transporters, which are independently and differentially regulated by glucose and insulin.