Properties of Na,K-ATPase in cerebellum of male and female rats: effects of acute and prolonged diabetes.

The present study was oriented to gender specificity of Na,K-ATPase in cerebellum, the crucial enzyme maintaining the intracellular homeostasis of Na ions in healthy and diabetic Wistar rats. The effects of diabetes on properties of the Na,K-ATPase in cerebellum derived from normal and streptozotocin (STZ)-diabetic rats of both genders were investigated. The samples were excised at different time intervals of diabetes induced by STZ (65 mg kg-1) for 8 days and 16 weeks. In acute 8-day-lasting model of diabetes, Western blot analysis showed significant depression of α1 isoform of Na,K-ATPase in males only. On the other hand, concerning the activity, the enzyme seems to be resistant to the acute model of diabetes in both genders. Prolongation of diabetes to 16 weeks was followed by increasing the number of active molecules of Na,K-ATPase exclusively in females as indicated by enzyme kinetic studies. Gender specificity was observed also in nondiabetic animals revealing higher Na,K-ATPase activity in control males probably caused by higher number of active enzyme molecules as indicated by increased value of V max when comparing to control female group. This difference seems to be age dependent: at the age of 16 weeks, the V max value in females was higher by more than 90%, whereas at the age of 24 weeks, this difference amounted to only 28%. These data indicate that the properties of Na,K-ATPase in cerebellum, playing crucial role in maintaining the Na+ and K+ gradients, depend on gender, age, and duration of diabetic impact.

Effect of duration of diabetes mellitus type 1 on properties of Na, K-ATPase in cerebral cortex.

Time sequence study was performed to characterize the effects of diabetes mellitus type 1 on properties of the Na, K-ATPase in cerebral cortex derived from normal and streptozotocin (STZ)-diabetic rats of both genders. The samples were excised at varying time intervals of diabetes induced by STZ (65 mg kg(-1)) for 8 days, and 8 and 16 weeks. Expression of α1-3 isoforms of Na, K-ATPase was not altered in statistically significant level during all stages of diabetes neither in female nor in male rats as revealed from Western blot analysis. Studies of kinetic properties of the enzyme resulted in variations in active number of Na, K-ATPase molecules as well as its qualitative properties. Sixteen-week-old control male rats showed better affinity to substrate as indicated by 13 % decrease of K m value. The effect persisted also in males subjected to 8 days lasting diabetes; however, in males subjected to 8 weeks lasting diabetes, the effect was lost. In 25-week-old rats, the Na, K-ATPase revealed again altered properties in males and females but the mechanism of the variation was different. In females, the number of active molecules of Na, K-ATPase was higher by 32 % in controls and by 17 % in rats with chronic diabetes when comparing to respective male groups as suggested by increased value of V max. So the properties of Na, K-ATPase in cerebral cortex, playing crucial role in maintaining intracellular homeostasis of Na(+) ions, depend on gender, age, and duration of diabetic insult.

Effects of γ-irradiation on Na,K-ATPase in cardiac sarcolemma.

Previous studies showed that adverse effect of ionizing radiation on the cardiovascular system is beside other factors mostly mediated by reactive oxygen and nitrogen species, which deplete antioxidant stores. One of the structures highly sensitive to radicals is the Na,K-ATPase the main system responsible for extrusion of superfluous Na(+) out of the cell which utilizes the energy derived from ATP. The aim of present study was the investigation of functional properties of cardiac Na,K-ATPase in 20-week-old male rats 6 weeks after γ-irradiation by a dose 25 Gy (IR). Irradiation induced decrease of systolic blood pressure from 133 in controls to 85 mmHg in IR group together with hypertrophy of right ventricle (RV) and hypotrophy of left ventricle (LV). When activating the cardiac Na,K-ATPase with substrate, its activity was lower in IR in the whole concentration range of ATP. Evaluation of kinetic parameters revealed a decrease of the maximum velocity (V max) by 40 % with no changes in the value of Michaelis-Menten constant (K m). During activation with Na(+), we observed a decrease of the enzyme activity in hearts from IR at all tested Na(+) concentrations. The value of V max decreased by 38 %, and the concentration of Na(+) that gives half maximal reaction velocity (K Na) increased by 62 %. This impairment in the affinity of the Na(+)-binding site together with decreased number of active Na,K-ATPase molecules, as indicated by lowered V max values, are probably responsible for the deteriorated efflux of the excessive Na(+) from the intracellular space in hearts of irradiated rats.