Figure 4. Effects of the Y522S mutation on mitochondrial structure and muscle function.

A–F. Mitochondrial ultrastructure is altered in muscle of RyR1^Y522S/wt mice. A. Mitochondria of RyR1^wt/wt fibers at 2–3 months of age are usually regularly shaped, appearing either round (panels 1 and 2) or slightly elongated (panel 3), with a dark/dense internal matrix. Abnormal mitochondria (panel 4) are rare in RyR1^wt/wt fibers. B. In RyR1^Y522S/wt fibers, some normal mitochondria are present (panel 1), but abnormal mitochondria are frequent (panels 2–4). C–F. At 1 year, a much larger percentage of mitochondria are severely swollen/disrupted than at 2–3 months of age in both in FDB and soleus muscles from RyR1^Y522S/wt mice (D and F, stars). In wt FDB (C) and soleus (E) muscles, on the other hand, mitochondria appear similar to those at 2–3 month of age. G. Mitochondrial lipid peroxidation in young and aged mice. Mitochondrial enriched fractions from 2 or 12 month-old mice with or without chronic NAC-treatment (≥ 2 months) were isolated and TBARS were measured in acid supernatants after protein precipitation, as detailed in Methods. Shown are the mean of 3 independent determinations ± SD. H–J. Effect of chronic NAC treatment on skeletal muscle function of aged mice. One year old male RyR1^wt/wt and RyR1^Y522S/wt mice were treated with NAC (1% w/v) in their drinking water for at least 2 months prior to sacrifice. Solei were removed and stimulated in vitro, as described in Experimental Procedures. Shown are data for stress developed at increasing frequency of electrical stimulation (H) and the maximal tension per cross-sectional area obtained by maximal electrical stimulation (I) or application of 20mM caffeine (J). All data in this figure are shown as mean ± S.E.M.