MUSCLE CONTRACTILE ACTIVITY MODULATES GLUT4 PROTEIN-CONTENT IN THE ABSENCE OF INSULIN

We examined whether muscle contractile activity directly modulates GLU T4 protein content in rat skeletal muscle without the participation of insulin action or via amplified insulin action. To attain this purpos e, the effects of increased, by training, or eliminated, by denervatio n, muscle contractile activity on muscle GLUT4 protein concentration w ere investigated in severely insulin-deficient diabetic rats. For the first set of experiments, insulin-deficient diabetic rats (induced by injection of 80 mg/kg B.W. streptozotocin) were trained for three week s by treadmill running (90 min/day, 19 m/min, 10%, 6 days/week). GLUT4 protein concentration in soleus muscle was increased by 48% (p < 0.01 ) as compared with diabetic sedentary animals. For the second set of e xperiments, rats were injected with streptozotocin (100 mg/kg). The mu scles innervated by the sciatic nerve of one leg were denervated four days after injection of streptozotocin. Three bays after denervation, soleus muscles in both legs were excised. Insulin deficiency decreased GLUT4 protein concentration in innervated soleus muscle. In insulin-d eficient diabetic rats, denervation also decreased soleus GLUT4 protei n concentration by 50% (p < 0.01) as compared with the contralateral i nnervated muscle. Furthermore, the effects of insulin-deficiency and d enervation on GLUT4 protein concentration were additive. These results provide evidence that muscle contractile activity directly modulates skeletal muscle GLUT4 protein concentration independent of insulin act ion.