Table 3.

Ultrastructural morphometry of CRUs and mitochondria in EDL and soleus muscles

	Column I Junctional SR width (nm)	Column II No of RyRs (10 μm2 of sectional area)−1	Column III Total SR volume (%)	Column IV No of mitochondria profiles (100 μm2 sectional area)−1
EDL
Wild type (n = 3)	62.4 ± 10.5 (n = 716)	39.2 ± 16.7 (n = 143)	5.66 ± 1.80 (n = 93)	36.3 ± 14.2 (n = 98)
CS1-null (n = 3)	25.0 ± 4.5† (n = 487)	71.8 ± 26.3† (n = 111)	5.25 ± 1.95 (n = 97)	62.1 ± 21.7† (n = 125)
Soleus
Wild type (n = 3)	62.5 ± 11.7 (n = 308)	36.0 ± 15.3 (n = 54)	–	80.0 ± 18.8 (n = 85)
CS1-null (n = 3)	30.0 ± 5.9† (n = 404)	32.7 ± 13.9 (n = 74)	–	81.4 ± 9.2 (n = 132)

Column I, the profile of the SR terminal cisternae appears different and its width, measured as shown in the panels A–D, is much smaller in CS1-null than in WT fibres of both EDL and soleus. In soleus muscle, CRUs are still formed by three elements, whereas junctions in EDL fibres are often formed by multiple elements (panel B). Column II, this reorganization of CRUs results in a large increase of RyR content in EDL fibres. Column III, on the other hand, the total SR volume (in relation to the total fibre volume) in CS1-null fibres is still very similar to that of WT fibres. Column IV, CS1-null EDLs present also a large increase in the average density of mitochondria, that may be related to the decreased fatigability of these muscles (see Fig. 4). Values are mean ± s.d.

^†Significantly different from WT group at P < 0.0001. Scale bar: A–D, 0.1 μm.