High glucose inhibits glucose uptake in renal proximal tubule cells by oxidative stress and protein kinase C

Background. High glucose has been considered to play an important role in alteration of renal proximal tubule transporter's activity. This study examined the mechanism by which high glucose modulates alpha-methyl-D-glucopyranoside (alpha-MG) uptake in primary cultured rabbit renal proximal tubule cells (PTCs). Methods. PTCs were incubated with 25 mmol/L glucose alone or combined with taurine. ascorbic acid, catalase. staurosporine. and bisindolylmaleimide I. Then alpha-MG uptake and lipid peroxide (LPO) formation were examined. Results. Twenty-five mmol/L glucose from four hours, but not 25 mmol/L mannitol. inhibited alpha-MG uptake by 23% compared with 5 mmol/L glucose (control). In the study to examine the relationship of oxidative stress in the high-glucose-induced inhibition of alpha-MG uptake. 25 mmol/L glucose significantly increased LPO by 27% compared with control. However. 10 mmol/L glucose did not affect alpha-MG uptake and LPO formation. Taurine (2 mmol/L), ascorbic acid (1 mmol/L), endogenous antioxidants, or catalase (600 U/mL) significantly blocked 25 mmol/L glucose-induced increase of LPO formation and inhibition of alpha-MG uptake. In the experiment to examine the effects of protein kinase C on LPO formation, 12-O-tetradecanoylphorbol-13-acetate (TPA: 100 ng/mL) increased LPO formation. and staurosporine (10(-7) mol/L) and bisindolylmaleimide I (10(-6) mol/L) totally blocked 25 mmol/L glucose-induced increase of LPO formation and inhibition of alpha-MG uptake. In addition, taurine reduced TPA-induced increase of LPO formation and inhibition of alpha-MG uptake. Conclusion. High glucose induces. in part. the inhibition of alpha-MG uptake through LPO formation, and activation of protein kinase C may play a role in high-glucose-induced LPO formation in the primary cultured rabbit renal PTCs.