Cell surface GLUT4 levels in skeletal muscle from nine type 2 diabetic subjects and nine healthy control subjects have been assessed by a new technique that involves the use of a biotinylated photo-affinity label. A profound impairment in GLUT4 translocation to the skeletal muscle cell surface in response to insulin was observed in type 2 diabetic patients. Levels of insulin-stimulated cell surface GLUT4 above basal in type 2 diabetic patients were only approximately 10% of those observed in healthy subjects. The magnitude of the defect in GLUT4 translocation in type 2 diabetic patients was greater than that observed for glucose transport activity, which was approximately 50% of that in healthy subjects. Reduced GLUT4 translocation is therefore a major contributor to the impaired glucose transport activity in skeletal muscle from type 2 diabetic subjects. When a marked impairment in GLUT4 translocation occurs, the contribution of other transporters to transport activity becomes apparent. In response to hypoxia, marked reductions in skeletal muscle cell surface GLUT4 levels were also observed in type 2 diabetic patients. Therefore, a defect in a common late stage in signal transduction and/or a direct impairment in the GLUT4 translocation process accounts for reduced glucose transport in type 2 diabetic patients.

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