Quantifying Mitochondrial Ultrastructure in Muscles

The mitochondrial ultrastructure of the soleus and gastrocnemius muscles was evaluated using TEM as previously described [35 (link)]. Images were taken at 10.000-fold magnification and ten random pictures from both muscles of each mouse were analyzed using the ImageJ software (Scion Image, National Institutes of Health, Bethesda, USA). Mean mitochondrial size was determined by manually encircling all identified mitochondria. Alterations on mitochondrial architecture were assessed by the categorization “normal” or “damaged” as follows: Mitochondria showing a loss of more than 50% of the cristae or a disruption of more than 50% of the outer membrane were assigned to “damaged” or otherwise to “normal.” The results were given as the percentage of the total number of mitochondria. Moreover, the percentage of swollen mitochondria and mitochondria containing multi-lamellar bodies was determined.