Age-related differences in the adaptive potential of type I skeletal muscle fibers.

This study was designed to investigate whether the relationship of fiber size and force is maintained with aging and inactivity. We hypothesized that fiber size and fiber force-generating capacity would decrease in parallel, thus resulting in no change in specific force with either age or inactivity. Thirty male Fischer 344/Brown Norway F1 hybrid rats, 6-23-month old (young adult), 24-33-month old (middle-aged) and 34-40 month old (old) were hindlimb unweighted for 14 days.

Altered proteasome structure, function, and oxidation in aged muscle.

The proteasome is the main protease for degrading oxidized proteins. We asked whether altered proteasome function contributes to the accumulation of oxidized muscle proteins with aging. Proteasome structure, function, and oxidation state were compared in young and aged F344BN rat fast-twitch skeletal muscle.

Myofibrillar myosin ATPase activity in hindlimb muscles from young and aged rats.

We tested the hypothesis that Ca(2+)-activated myosin ATPase activity is lower in muscles of aged rats relative to muscles of young rats, independent of changes in myosin isoform expression. Myofibrils were prepared from permeabilized fibers of soleus, plantaris, and semimembranosus muscles of young (8-12 months) and aged (32-38 months) F344 x BN rats and assayed for resting myosin ATPase, Ca(2+)-activated myosin ATPase, and myosin heavy chain (MHC) and myosin light chain (MLC) isoform compositions. Resting myosin ATPases were not affected by age in any muscle (P > or = 0.

Altered proteasome function and subunit composition in aged muscle.

Myofibrillar protein degradation is mediated through the ubiquitin-proteasome pathway. To investigate if altered proteasome activity plays a role in age-related muscle atrophy, we examined muscle size and proteasome function in young and aged F344BN rats. Significant age-related muscle atrophy was confirmed by the 38% decrease in cross-sectional area of type 1 fibers in soleus muscle.