INSULIN-STIMULATED GLUT-4 TRANSLOCATION IN HUMAN SKELETAL-MUSCLE - A QUANTITATIVE CONFOCAL MICROSCOPIC ASSESSMENT

Insulin stimulation of glucose transport in skeletal muscle is conside red to involve translocation of the skeletal muscle/adipose tissue glu cose transporter isoform, Glut 4, from cytosolic vesicles to the cell surface. The current study was undertaken to investigate Glut 4 transl ocation in skeletal muscle of healthy volunteers during euglycaemic in sulin infusion. Previous quantitative studies of glucose transport hav e depended on differential centrifugation methods, which demand large biopsy samples. In this study we have developed and applied a quantita tive method using confocal laser microscopy, well suited to the small needle biopsies that are typically available clinically. Percutaneous biopsy of vastus lateralis skeletal muscle was performed during basal and euglycaemic insulin-stimulated conditions, and Glut 4 translocatio n was assessed using immunohistochemical labelling and confocal laser microscopy imaging in 14 healthy lean subjects. At physiological hyper insulinaemia (536 +/- 16 pM), mean systemic glucose utilization was 9. 27 +/- 0.78 mg/kg-min, indicative of normal insulin sensitivity. The p resence of Glut 4 at the sarcolemma increased significantly (p < 0.01) , with a ratio of insulin-stimulated to basal. sarcolemmal Glut 4 of 1 .85 +/- 0.33, indicative of insulin-stimulated Glut 4 translocation. T he area of Glut 4-labelled sites also increased significantly (p (0.01 ) in response to insulin infusion; this ratio was 1.56 +/- 0.13. Thus, at physiological hyperinsulinaemia, the amount of Glut 4 at the cell surface of skeletal muscle in healthy, lean individuals increases appr oximately twofold over basal conditions, and this process can be measu red using immunohistochemical labelling imaged by confocal laser scann ing microscopy.