Skeletal muscle buffering capacity is higher in the superficial vastus than in the soleus of spontaneously running rats

Abstract

Skeletal muscle buffering capacity (βm_titr) was determined in soleus (type I) and superficial vastus (type II) muscles of 16 Long–Evans rats with differing levels of spontaneous activity and in 11 sedentary control rats. βm_titr was 24% higher (P+ g muscle dry wt^-1 pH unit^-1) (mean±SD). There was no relationship between βm_titr and mean weekly running distance amongst spontaneously running rats, nor was βm_titr any greater in these rats than in a group of sedentary control rats. Protein to wet wt ratio was 31% higher (P-1), but there was no relationship between protein to wet wt ratio and running distance. Initial muscle homogenate pH (pH_i) was lower in superficial vastus muscle compared with soleus muscle (6.36±0.25 vs. 6.63±0.16). Running rats had a significantly lower pH_i in both soleus and superficial vastus than sedentary controls. There was an exponential relationship between weekly running distance and pH_i in both the superficial vastus muscle (r=-0.86, Pr=-0.73, Pr=0.66, Ptitr in the type II superficial vastus muscle when compared with the predominantly type I soleus muscle. We suggest that this may be partly the result of a higher protein concentration in type II muscle. Future studies measuring βm_titr in mixed muscle (e.g. human vastus lateralis) should report fibre type composition.