Use of a novel impermeable biotinylated photolabeling reagent to assess insulin- and hypoxia-stimulated cell surface GLUT4 content in skeletal musclefrom type 2 diabetic patients

Cell surface GLUT4 levels in skeletal muscle from nine type 2 diabetic subj ects and nine healthy control subjects have been assessed by a new techniqu e that involves the use of a biotinylated photo-affinity label, A profound impairment in GLUT4 translocation to the skeletal muscle cell surface in re sponse to insulin was observed in type 2 diabetic patients. Levels of insul in-stimulated cell surface GLUT4 above basal in type 2 diabetic patients me re only similar to 10% of those observed in healthy subjects. The magnitude of the defect in GLUT4 translocation in type 2 diabetic patients was great er than that observed for glucose transport activity, which was similar to 50% of that in healthy subjects. Reduced GLUT4 translocation is therefore a major contributor to the impaired glucose transport activity in skeletal m uscle from type 2 diabetic subjects. When a marked impairment in GLUT4 tran slocation occurs, the contribution of other transporters to transport activ ity becomes apparent. In response to hypoxia, marked reductions in skeletal muscle cell surface GLUT4 levels were also observed in type 2 diabetic pat ients. Therefore, a defect in a common late stage in signal transduction an d/or a direct impairment in the GLUT4 translocation process accounts for re duced glucose transport in type 2 diabetic patients.