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

Brett A. Osborn, June T. Daar, Richard A. Laddaga, Fred D. Romano, and Dennis J. Paulson Department of Physiology, Midwestern University, Downers Grove, Illinois 60515 Received 7 May 1996; accepted in final form 28 October 1996. Osborn, Brett A., June T. Daar, Richard A. Laddaga, Fred D. Romano, and Dennis J. Paulson. Exercise training increases sarcolemmal GLUT-4 protein and mRNA content in diabetic heart. J. Appl. Physiol. 82(3): 828-834, 1997. 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 ( p NPPase; an indicator of Na + -K + -adenosinetriphosphatase activity) was quantified. Hearts from the sedentary diabetic group exhibited a significant depression of sarcolemmal p NPPase activity. Exercise training did not significantly alter p NPPase 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 myocardial glucose oxidation; diabetic cardiomyopathy 0161-7567/97 $5.00 Copyright © 1997 the American Physiological Society