Fig. 6.

Changes in activity of the 20S and 26S β₂ proteasome subunit in adult and old rats during hindlimb unloading (HU). Proteolytic activity of the β₂-subunit of the 20S (ATP-independent) and 26S (ATP-dependent) proteasome was measured in the soleus (A), medial gastrocnemius (MG; B), and tibialis anterior (TA; C) muscles of adult (9 mo, □) and old (29 mo, ■) rats after 3, 7, and 14 days of HU. Data are expressed as a percentage relative to the activity of the adult control group (n = 4–6/group). Values are means ± SE. *P < 0.05 vs. adult control. #P < 0.05 vs. old control. ^ϕP < 0.05 vs. adult at same time point.