Chronic aerobic exercise enhances components of the classical and novel insulin signalling cascades in Sprague-Dawley rat skeletal muscle

Aim: The aim of this study was to provide a more extensive evaluation of the effects of chronic aerobic exercise on various components of the insulin signalling cascade in normal rodent skeletal muscle because of the limited body of literature that exists in this area of investigation. Methods: Male Sprague-Dawley rats were assigned to either control (n = 7) or chronic aerobic exercise (n = 7) groups. Aerobic exercise animals were run 3 day week(-1) for 45 min on a motor-driven treadmill (32 m min(-1), 15% grade) for a 12 week period. Following the training period, all animals were subjected to hind limb perfusion in the presence of 500 mu U mL(-1) insulin to determine what effect chronic aerobic training had on various components of the insulin signalling cascade, c-Cbl protein concentration and c-Cbl phosphorylation. Results: Twelve weeks of aerobic training did not alter skeletal muscle Akt 1/2 protein concentration, Akt Ser 473 phosphorylation, Akt Thr 308 phosphorylation, Akt 1 activity, aPKC-zeta protein concentration, aPKC-lambda protein concentration or c-Cbl protein concentration. In contrast, chronic aerobic exercise increased insulin-stimulated phosphatidylinositol 3-kinase, Akt 2 kinase and aPKC-zeta/lambda kinase activities, as well as c-Cbl tyrosine phosphorylation, in a fibre type specific response to aerobic training. In addition, chronic aerobic exercise enhanced insulin-stimulated plasma membrane glucose transporter 4 (GLUT4) protein concentration. Conclusion: Collectively, these findings suggest that chronic aerobic exercise enhances components of both the classical and novel insulin signalling cascades in normal rodent skeletal muscle, which may contribute to an increased insulin-stimulated plasma membrane GLUT4 protein concentration.