Figure 7

Muscle function. (A) Force frequency relationship for the soleus of eight-week-old mice. (B) Force- frequency relationship for the EDL of eight-week-old mice. (C) Fatigue plotted as % initial force in the soleus of eight-week-old mice. (D) Fatigue plotted as % initial force in the EDL of eight-week-old mice. (E) Force frequency relationship for the soleus of mice over nine months old (F) Fatigue plotted as % initial force in the EDL of mice over nine months old. (G and H) Representative images from muscle (soleus and EDL, respectively) sections pseudo colored for the different fiber types are shown. Primary antibodies against MHC I (clone BA-F8) and IIa (clone sc-71) were probed in the same sections to detect type I (red) and type IIa (green) fibers and antibody for MHC IIb (clone BF-F3) was used in different sections for the detection of type IIb fibers (red), bar is 100 μm. (I and J) Fiber type distributions in soleus and EDL, respectively. (K and L) Evaluation of average cross-sectional area (CSA) for the soleus and EDL, respectively. Fibers from seven mice of each genotype were analyzed. Number of individual fibers in soleus measured: type I: 980 (WT), 1,116 (EK); IIA: 1,898 (WT), 1,980 (EK), IIb/x: 417 (WT), 407 (EK). Number of individual fibers in EDL measured: IIA: 612 (WT), 505 (EK), IIb/x: 1,965 (WT), 2,323 (EK). Values in bar graphs are presented as mean ± SEM, n numbers are indicated. *P <0.05, **P <0.01, and ***P <0.001.