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Departments of Pathology and of Endocrinology, Odense University Hospital, DK-5000 Odense; and Department of Physiology, Panum Institute, University of Copenhagen, DK-2200 Copenhagen, Denmark
GLUT-4 expression in individual fibers of
human skeletal muscles in younger and older adults was studied.
Furthermore, the dependency of insulin-stimulated glucose uptake on
fiber type distribution was investigated. Fiber type distribution was
determined in cryosections of muscle biopsies from 8 younger (29 yr)
and 8 older (64 yr) healthy subjects, and estimates of GLUT-4
expression in individual fibers were obtained by combining
immunohistochemistry and stereology. GLUT-4 was more abundantly
expressed in slow compared with fast muscle fibers in both younger
(P < 0.007) and older (P < 0.001) subjects. A 25%
reduction of GLUT-4 density in fast fibers (P < 0.001) and an
unchanged GLUT-4 density in slow fibers were demonstrated in older
compared with younger subjects. Insulin-stimulated glucose uptake rates
measured by hyperinsulinemic, euglycemic clamp were not correlated with
the fraction of slow fibers in the young (r =
0.45,
P > 0.25) or in the elderly (r = 0.11, P > 0.75) subjects. In conclusion, in human skeletal muscle, GLUT-4 expression is fiber type dependent and decreases with age, particularly in fast muscle fibers.
aging; glucose uptake; immunohistochemistry; stereology; slow fibers
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