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DEVELOPMENT AND TISSUE PLASTICITY
1Department of Pharmacology, Milton S. Hershey Medical Center, College of Medicine, The Pennsylvania State University, Hershey, Pennsylvania 17033-0850; and2Department of Integrative Physiology, University of Colorado, Boulder, Colorado 80309
Submitted 13 May 2003 ; accepted in final form 5 June 2003
The present study tests the hypothesis that endurance exercise training
(ETr) reverses age-associated alterations in expression of
Na+-K+-ATPase subunit isoforms in rat skeletal muscles.
Expression of the isoforms was examined in 16-mo-old sedentary middle-aged,
29-mo-old sedentary senescent, and 29-mo-old treadmill exercise-trained
senescent Fischer 344 x Brown Norway rats. Levels of the
1-isoform increased with age in red gastrocnemius (GR),
white gastrocnemius (GW), and extensor digitorum longus (EDL) muscles, and ETr
further increased its levels. Levels of the
2-isoform were
unchanged in GR, had a strong trend for a decrease in GW, and decreased
significantly in EDL. ETr increased expression of the
2-isoform in all three muscle groups. There was no increase
in expression of the
1-isoform in GR, GW, or EDL with age,
whereas ETr markedly increased its levels in the muscles. There was a marked
decrease with age in expression of the
2-isoform in the
muscle groups that was not reversed by ETr. By contrast,
3-isoform levels increased with age in GR and GW, and ETr was
able to reverse this increase. Na+-K+-ATPase enzyme
activity was unchanged with age in GR and GW but increased in EDL. ETr
increased enzyme activity in GR and GW and did not change in EDL. Myosin heavy
chain isoforms in the muscle groups did not change significantly with age; ETr
caused a general shift toward more oxidative fibers. Thus ETr differentially
modifies age-associated alterations in expression of
Na+-K+-ATPase subunit isoforms, and a mechanism(s) other
than physical inactivity appears to play significant role in some of the
age-associated changes.
-subunit;
-subunit; aging; gastrocnemius; extensor digitorum longus; myosin heavy chain
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