GLUCOSE-INDUCED CHANGES IN TURNOVER OF NA+ H+ EXCHANGER OF IMMORTALIZED LYMPHOBLASTS FROM TYPE-I DIABETIC-PATIENTS WITH NEPHROPATHY/

Increased cellular Na+/H+ exchanger (NHE) activity has been demonstrat ed in type I diabetic patients with nephropathy. Such patients also ha ve a previous history of poor glycemic control. The interaction betwee n hyperglycemia and changes in NHE activity remains obscure. Therefore , we examined the effects of media containing 5 and 25 mmol/l glucose on the increased NHE activity and turnover number in Epstein-Barr viru s-transformed lymphoblasts from patients with diabetic nephropathy com pared with normoalbuminuric diabetic and nondiabetic control subjects. NHE activity was determined fluorometrically, and MIE isoform 1 (NHE- 1) density was measured with specific polyclonal antibodies. In the pr esence of 5 mmol/l glucose, cells from patients with diabetic nephropa thy exhibited higher NHE activity with intracellular pH clamped to 6.0 compared with diabetic and nondiabetic control subjects (P < 0.005 fo r both), due to a higher turnover number of NHE-1. Incubation in 25 mm ol/l glucose for 48 h caused an increase in NHE activity (P < 0.001) a nd turnover number (P < 0.01) in the diabetic nephropathy group only w ith no significant change in the diabetic or nondiabetic control group s. The rate constants for cell proliferation and NHE activity or turno ver number were correlated when cells were cultured in 5 mmol/l glucos e (r = 0.34 and 0.32, respectively; P < 0.05) or 25 mmol/l glucose med ia (r = 0.66 and 0.65, respectively; P < 0.001). We conclude that only lymphoblasts from the diabetic nephropathy group show an increase in NHE activity and turnover number under conditions mimicking hyperglyce mia. Thus, high glucose levels exaggerate the differences in NHE activ ity, turnover number, and cell proliferation rate already present betw een cells from diabetic nephropathy patients and those from diabetic a nd nondiabetic control subjects.