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Na+/K(+)-ATPase activity in vascular smooth muscle from streptozotocin diabetic rat
J M Smith1, D J Paulson, S M Solar
1Department of Physiology, Midwestern University, Downers Grove, IL 60515, USA.
Objectives:
Insulin-deficient diabetes impairs carbohydrate metabolism in a variety of tissues. Vascular smooth muscle may be susceptible to the diabetes-induced disturbance in glycolysis since Na+/K(+)-ATPase in this tissue preferentially utilizes ATP generated by glycolysis. The purpose of this study was to determine if chronic exposure to the metabolic alterations associated with insulin-deficient diabetes directly inhibited Na+/K(+)-ATPase activity, or its regulation, in vascular smooth muscle.
Methods:
Diabetes was induced by intravenous administration of streptozotocin (60 mg/kg). After 12 weeks, Na+/K(+)-ATPase activity in aorta and superior mesenteric artery was evaluated under a variety of conditions. Na+/K(+)-ATPase was estimated by measuring the influx of rubidium-86 (86Rb) in the presence or absence of the Na+/K(+)-ATPase inhibitor, ouabain. The metabolism of [3H]glucose and [14C]glucose was used to estimate glycolysis or glucose oxidation, respectively.
Results:
Glycolysis and glucose oxidation were decreased in aortic smooth muscle (27 and 34%, respectively). An intact endothelium was associated with a marked decrease in ouabain-sensitive (pump-mediated) 86Rb uptake in diabetic aorta. However, ouabain-sensitive 86Rb uptake was similar in de-endothelialized aorta and superior mesenteric artery from diabetic and non-diabetic rats under both unstimulated conditions and during maximal stimulation. Removal of glucose or oxygen reduced ouabain-sensitive 86Rb uptake to a similar extent in both groups. In contrast, the receptor-mediated stimulation of ouabain-sensitive 86Rb uptake by insulin was decreased.
Conclusions:
These results suggest that intrinsic Na+/K(+)-ATPase activity is not diminished in diabetic vascular smooth muscle under physiological conditions and that the impairment of cellular metabolism in diabetic blood vessels does not limit stimulation of Na+/K(+)-ATPase activity. However, modulation of Na+/K(+)-ATPase activity by endothelial factors or insulin appears to be altered in aorta from diabetic rats.
Insights
Insulin-deficient diabetes does not impair vascular smooth muscle Na+/K(+)-ATPase activity directly. However, endothelial factors and insulin regulation of this enzyme are altered in diabetic aorta.
Area of Science:
- Vascular biology
- Metabolic disorders
- Cellular physiology
Background:
- Insulin-deficient diabetes disrupts carbohydrate metabolism.
- Vascular smooth muscle relies on glycolysis for ATP production, fueling Na+/K(+)-ATPase.
- Potential for diabetes to impair Na+/K(+)-ATPase in vascular smooth muscle.
Purpose of the Study:
- To investigate if chronic metabolic changes in diabetes directly inhibit Na+/K(+)-ATPase activity in vascular smooth muscle.
- To assess the regulation of Na+/K(+)-ATPase in diabetic vascular tissue.
Main Methods:
- Streptozotocin-induced diabetes in rats (12 weeks).
- Evaluation of Na+/K(+)-ATPase activity using rubidium-86 uptake in aorta and superior mesenteric artery.
- Assessment of glycolysis and glucose oxidation via radiolabeled glucose metabolism.
- Experiments with intact vs. de-endothelialized vessels, and varying substrate/stimulator conditions.
Main Results:
- Diabetic aortic smooth muscle showed reduced glycolysis and glucose oxidation.
- Ouabain-sensitive rubidium-86 uptake was decreased in diabetic aorta with intact endothelium.
- Na+/K(+)-ATPase activity was comparable in de-endothelialized diabetic and non-diabetic vessels.
- Insulin-mediated stimulation of Na+/K(+)-ATPase was impaired in diabetic aorta.
Conclusions:
- Intrinsic Na+/K(+)-ATPase activity is preserved in diabetic vascular smooth muscle under physiological conditions.
- Impaired cellular metabolism in diabetes does not limit Na+/K(+)-ATPase stimulation.
- Endothelial factors and insulin signaling alter Na+/K(+)-ATPase modulation in diabetic aorta.