Glucose-Induced Regulation of NHEs Activity and SGLTs Expression Involves the PKA Signaling Pathway

The effect of glucose on the intracellular pH (pHi) recovery rate (dpHi/dt) and Na+-glucose transporter (SGLT) localization was investigated in HEK-293 cells, a cell line that expresses endogenous NHE1, NHE3, SGLT1, and SGLT2 proteins. The activity of the Na+/H+ exchangers (NHEs) was evaluated by using fluorescence microscopy. The total and membrane protein expression levels were analyzed by immunoblotting. In cells cultivated in 5 mM glucose, the pHi recovery rate was 0.169 ± 0.020 (n = 6). This value did not change in response to the acute presence of glucose at 2 or 10 mM, but decreased with 25 mM glucose, an effect that was not observed with 25 mM mannitol. Conversely, the chronic effect of high glucose (25 mM) increased the pHi recovery rate (~40%, P < 0.05), without changes in the total levels of NHE1, NHE3, or SGLT1 expression, but increasing the total cellular (~50%, P < 0.05) and the plasma membrane (~100%, P < 0.01) content of SGLT2. Treatment with H-89 (10−6 M) prevented the stimulatory effect of chronic glucose treatment on the pHi recovery rate and SGLT2 expression in the plasma membrane. Our results indicate that the effect of chronic treatment with a high glucose concentration is associated with increased NHEs activity and plasma membrane expression of SGLT2 in a protein kinase A-dependent way. The present results reveal mechanisms of glucotoxicity and may contribute to understanding the diabetes-induced damage of this renal epithelial cell.