Expression of GLUT-4 glucose transporter in unweighted soleus muscle of normal and STZ-induced diabetic rats

Effects of 6 days of hindlimb suspension on expression of glucose transporters were studied in the skeletal muscle of nondiabetic and streptozotocin-induced diabetic rats. Although total membrane protein recovered from soleus muscles tended to decrease with suspension, GLUT-4 protein concentration (amount per gram membrane protein) was increased by 66 and 91% compared with weight-bearing control in nondiabetic and diabetic rats, respectively. Therefore, the amount of GLUT-4 protein in whole soleus muscle did not decrease with the hindlimb suspension in normal and diabetic rats. In contrast, hindlimb suspension decreased GLUT-4 mRNA amount in whole soleus muscle by 47 and 27% in nondiabetic and diabetic rats, respectively. Thus the GLUT-4 protein-to-GLUT-4 mRNA ratio was increased 2.1-fold in nondiabetic and 1.4-fold in diabetic rats. The extensor digitorum longus muscle, which generally shows little response to unweighting, exhibited no such changes. These results suggest that the amount of GLUT-4 glucose transporter in the unweighted soleus muscle was maintained via a translational and/or posttranslational mechanism in nondiabetic rats as well as in streptozotocin-induced diabetic rats under the condition of reduced weight-bearing activity.