Na,K-ATPase Kinetics and Oxidative Stress in Kidneys of Zucker Diabetic Fatty (fa/fa) Rats Depending on the Diabetes Severity-Comparison with Lean (fa/+) and Wistar Rats

Abstract

For a better insight into relations between type 2 diabetes mellitus (T2DM) and Na,K-ATPase properties in kidneys, we aimed to characterize two subgroups of ZDF obese (fa/fa) rats, with more and less developed T2DM, and compare them with two controls: lean (fa/+) and Wistar. Na,K-ATPase enzyme kinetics were estimated by measuring the ATP hydrolysis in the range of NaCl and ATP levels. As Na,K-ATPase is sensitive to oxidative stress, we evaluated selected oxidative stress parameters in kidney homogenates. Our results suggest that thiol-disulfide redox balance in the renal medulla and Na,K-ATPase properties in the renal cortex differ between both controls, while observed measurements in lean (fa/+) rats showed deviation towards the values observed in ZDF (fa/fa) rats. In comparison with both controls, Na,K-ATPase enzyme activity was higher in the renal cortex of ZDF rats independent of diabetes severity. This might be a consequence of increased glucose load in tubular fluid. The increase in lipid peroxidation observed in the renal cortex of ZDF rats was not associated with Na,K-ATPase activity impairment. Regarding the differences between subgroups of ZDF animals, well-developed T2DM (glycemia higher than 10 mmol/L) was associated with a higher ability of Na,K-ATPase to utilize the ATP energy substrate.

Keywords: ZDF rats; antioxidant state; carbonyl stress; fa/+; fa/fa; kidney; sodium pump; type 2 diabetes mellitus.

Figure 1

Activation of the Na,K-ATPase enzyme by cofactor Na⁺ in the renal cortex. (Panel a) Activation of the Na,K-ATPase by low concentrations of cofactor Na+. Inset: activation of the enzyme in the whole investigated concentration range of Na⁺ in Wistar rats (CW, n = 8), lean fa/+ (ZL, n = 8), and Zucker diabetic fatty (ZDF) fa/fa rats divided into ZO (ZDF fa/fa obese, glycemia < 10 mmol·L⁻¹, n = 8) and ZOD (ZDF fa/fa obese diabetic, glycemia > 10 mmol·L⁻¹, n = 8) groups. Error bars are not depicted, as they are shorter than the size of the symbols. (Panel b) V_max values in all experimental groups. (Panel c) K_Na values in all experimental groups. The animals were sacrificed at the age of 38–39 weeks. Data represent means ± standard errors of mean. For statistical analyses, one-way analysis of variance with Tukey’s post hoc test was used: a: p < 0.05, b: p < 0.01, d: p < 0.0001 vs. CW; e: p < 0.05, g: p < 0.001 vs. ZL.

Figure 2

Activation of the Na,K-ATPase enzyme by substrate ATP in the renal cortex. (Panel a) Activation of the Na,K-ATPase by low concentrations of substrate ATP. Inset: activation of the enzyme in the whole investigated concentration range of ATP in Wistar rats (CW, n = 8), lean fa/+ (ZL, n = 8), and Zucker diabetic fatty (ZDF) fa/fa rats divided into ZO (ZDF fa/fa obese, glycemia < 10 mmol·L⁻¹, n = 8) and ZOD (ZDF fa/fa obese diabetic, glycemia > 10 mmol·L⁻¹, n = 8) groups. Error bars are not depicted, as they are shorter than the size of the symbols. (Panel b) V_max values in all experimental groups. (Panel c) K_m values in all experimental groups. The animals were sacrificed at the age of 38–39 weeks. Data represent means ± standard errors of mean. For statistical analyses, one-way analysis of variance with Tukey’s post hoc test was used: b: p < 0.01, d: p < 0.0001 vs. CW; f: p < 0.01 vs. ZL; i: p < 0.05 vs. ZO.