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1 Department of Pharmacology and Therapeutics, Faculty of Medicine, University of Calgary, Calgary, Alberta, Canada T2N 4N1; 2 Department of Medical Physiology, Institute of Medical Biology, University of Tromsø, N-9037 Tromsø, Norway; and 3 Department of Cardiovascular and Metabolic Diseases, Pfizer Global Research and Development, Groton, Connecticut 06340
Glucose and fatty acid metabolism was assessed in isolated working hearts from control C57BL/KsJ-m+/+db mice and transgenic mice overexpressing the human GLUT-4 glucose transporter (db/+-hGLUT-4). Heart rate, coronary flow, cardiac output, and cardiac power did not differ between control hearts and hearts overexpressing GLUT-4. Hearts overexpressing GLUT-4 had significantly higher rates of glucose uptake and glycolysis and higher levels of glycogen after perfusion than control hearts, but rates of glucose and palmitate oxidation were not different. Insulin (1 mU/ml) significantly increased glycogen levels in both groups. Insulin increased glycolysis in control hearts but not in GLUT-4 hearts, whereas glucose oxidation was increased by insulin in both groups. Therefore, GLUT-4 overexpression increases glycolysis, but not glucose oxidation, in the heart. Although control hearts responded to insulin with increased rates of glycolysis, the enhanced entry of glucose in the GLUT-4 hearts was already sufficient to maximally activate glycolysis under basal conditions such that insulin could not further stimulate the glycolytic rate.
glycolysis; glucose oxidation; glycogen; palmitate oxidation; glucose transporter 4 transgenic mice
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