Figure 9. Markers of endoplasmic reticulum (ER) stress in adult and old rats during hindlimb unloading (HU) and reloading. Representative Western blots and quantification of ER stress markers BiP (A), PDI (B), and CHOP (C) in the soleus and tibialis anterior (TA) muscles of adult (9 mo, open squares) and old (29 mo, filled squares) rats following 14 days of HU and after 3, 7, and 14 days of reloading. Total protein, determined by stain-free imaging of the PVDF membrane, was used to normalize protein expression. Data are expressed as a percentage relative to the adult control group for each protein (n=4-6/group). Values are mean ± SEM, *p<0.05 vs adult control, #p<0.05 vs old control, φp<0.05 vs adult at same time point.