Exercise training increases sarcolemmal GLUT-4 protein and mRNA content in diabetic heart

This study determined whether dynamic exercise training of diabetic rats would increase the expression of the GLUT-4 glucose transport protein in prepared cardiac sarcolemmal membranes. Four groups were compared: sedentary control, sedentary diabetic, trained control, and trained diabetic. Diabetes was induced by intravenous streptozotocin (60 mg/kg). Trained control and diabetic rats were run on a treadmill for 60 min, 27 m/min, 10% grade, 6 days/wk for 10 wk. Sarcolemmal membranes were isolated by using differential centrifugation, and the activity of sarcolemmal K+-p-nitrophenylphosphatase (pNPPase; an indicator of Na+-K+-adenosinetriphosphatase activity) was quantified. Hearts from the sedentary diabetic group exhibited a significant depression of sarcolemmal pNPPase activity. Exercise training did not significantly alter pNPPase activity. Sedentary diabetic rats exhibited an 84 and 58% decrease in GLUT-4 protein and mRNA, respectively, relative to control rats. In the trained diabetic animals, sarcolemmal GLUT-4 protein levels were only reduced by 50% relative to control values, whereas GLUT-4 mRNA were returned to control levels. The increase in myocardial sarcolemmal GLUT-4 may be beneficial to the diabetic heart by enhancing myocardial glucose oxidation and cardiac performance.