Diabetes Decreases Na⁺-K⁺ Pump Concentration in Skeletal Muscles, Heart Ventricular Muscle, and Peripheral Nerves of Rat

Na⁺-K⁺-ATPase or the Na⁺-K⁺ pump is essential for some specific properties of muscle and nerve tissue such as contractility and excitability. Previous studies have shown conflicting variations in Na⁺-K⁺-ATPase activity or Na⁺-K⁺ pump concentration of muscle cells in experimental diabetes. Our study demonstrates that early untreated diabetes in rats induced by injection of streptozocin is associated with decreases in [³H]ouabain binding-site concentration of 24-48% in various skeletal muscles and 16% in peripheral nerves as well as a decrease in K⁺-dependent 3-O-methylfluorescein phosphatase activity of 21% in the heart ventricle. These effects could be prevented by insulin treatment. They probably represent a decrease in the concentration of Na⁺-K⁺ pumps. There was no evidence for more than one population of Na⁺-K⁺ pumps in intact samples of skeletal muscle and nerves from normal, diabetic, and insulin-treated animals. The decrease in Na⁺-K⁺ pump concentration in nerve cells may be due to atrophy of the axons. In skeletal muscles, myocardium, and peripheral nerves, the observed decrease in Na⁺-K⁺ pump concentration may be important for the pathophysiology of diabetes. We emphasize that quantification of Na⁺-K⁺-ATPase or the Na⁺-K⁺ pump in muscle and nerve tissue from diabetic animals should preferably be performed with either intact samples or crude homogenates of whole tissue.