The effects of insulin and beta-adrenergic stimulation on glucose transport, glut 4 and PKB activation in the myocardium of lean and obese non-insulin dependent diabetes mellitus rats.
Glucose uptake, glut 4 translocation and activation of protein kinase B were measured in Langendorff perfused hearts from (i) Wistar control, (ii) lean, neonatal Streptozotocin induced (Stz) and (iii) Zucker (fa/fa) obese diabetic rats of 10-12 weeks old. Hearts were subjected to stimulation with insulin, isoproterenol (beta-adrenergic agonist) or a combination of insulin and isoproterenol, during the perfusion protocol. Basal myocardial glucose uptake was impaired in both diabetic models, but could be stimulated significantly by insulin. In the Zucker rats, the time-course of insulin action was delayed. Insulin and beta-stimulation of glucose uptake were not additive. Evaluation of sarcolemmal membranes from these hearts showed that the affinity of glut 4 was significantly lower in the Zucker but not in the Stz hearts while a reduced affinity found with a combination of insulin and beta-stimulation in control hearts, was absent in both diabetic models. Total membrane lysates were analyzed for glut 4 expression while an intracellular component was generated to quantify translocation on stimulation as well as activity of protein kinase B (PKB). At this age, the neonatal Streptozotocin induced diabetic animals presented with more faulty regulation concerning adrenergic stimulated effects on elements of this signal transduction pathway while the Zucker fa/fa animals showed larger deviations in insulin stimulated effects. The overall response of the Zucker myocardium was poorer than that of the Stz group. No significant modulation of beta-adrenergic signaling on insulin stimulated glucose uptake was found. The PI-3-kinase inhibitor wortmannin, could abolish glucose uptake as well as PKB activation elicited by both insulin and isoproterenol.
Huisamen
B
B
Department of Medical Physiology and Biochemistry, Faculty of Medicine, University of Stellenbosch, Tygerberg, Republic of South Africa.
van Zyl
M
M
Keyser
A
A
Lochner
A
A
D000318:Adrenergic beta-Agonists / Q000494:pharmacology; D000818:Animals; D003920:Diabetes Mellitus / Q000378:metabolism; D003921:Diabetes Mellitus, Experimental; D003924:Diabetes Mellitus, Type 2 / Q000378:metabolism*; D004789:Enzyme Activation; D005947:Glucose / Q000378:metabolism*; D051275:Glucose Transporter Type 4; D006321:Heart / Q000187:drug effects; D066298:In Vitro Techniques; D007328:Insulin / Q000097:blood / Q000494:pharmacology*; D007545:Isoproterenol / Q000494:pharmacology*; D009004:Monosaccharide Transport Proteins / Q000235:genetics / Q000378:metabolism*; D009124:Muscle Proteins; D009206:Myocardium / Q000378:metabolism*; D009765:Obesity; D017346:Protein Serine-Threonine Kinases; D021381:Protein Transport / Q000502:physiology; D011518:Proto-Oncogene Proteins / Q000378:metabolism*; D051057:Proto-Oncogene Proteins c-akt; D051381:Rats; D017208:Rats, Wistar; D011924:Rats, Zucker
D000318:Adrenergic beta-Agonists; D051275:Glucose Transporter Type 4; D007328:Insulin; D009004:Monosaccharide Transport Proteins; D009124:Muscle Proteins; D011518:Proto-Oncogene Proteins; C495694:Slc2a4 protein, rat; D017346:Protein Serine-Threonine Kinases; D051057:Proto-Oncogene Proteins c-akt; D005947:Glucose; D007545:Isoproterenol