EXERCISE TRAINING INCREASES SARCOLEMMAL GLUT-4 PROTEIN AND MESSENGER-RNA CONTENT IN DIABETIC HEART

This study determined whether dynamic exercise training of diabetic ra ts would increase the expression of the GLUT-4 glucose transport prote in in prepared cardiac sarcolemmal membranes. Four groups were compare d: sedentary control, sedentary diabetic, trained control, and trained diabetic. Diabetes was induced by intravenous streptozotocin (60 mg/k g). Trained control and diabetic rats were run on a treadmill for 60 m in, 27 m/min, 10% grade, 6 days/wk for 10 wk. Sarcolemmal membranes we re 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 s edentary diabetic group exhibited a significant depression of sarcolem mal pNPPase activity. Exercise training did not significantly alter pN PPase activity. Sedentary diabetic rats exhibited an 84 and 58% decrea se in GLUT-4 protein and mRNA, respectively, relative to control rats. In the trained diabetic animals, sarcolemmal GLUT-4 protein levels we re only reduced by 50% relative to control values, whereas GLUT-4 mRNA were returned to control levels. The increase in myocardial sarcolemm al GLUT-4 may be beneficial to the diabetic heart by enhancing myocard ial glucose oxidation and cardiac performance.