title: Skeletal muscle buffering capacity is higher in the superficial vastus than in the soleus of spontaneously running rats.
abstract: Skeletal muscle buffering capacity (beta mtitr) 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. beta mtitr was 24% higher (P < 0.001) in superficial vastus muscle than in soleus muscle (268 +/- 50 vs. 216 +/- 30 mumol H+ g muscle dry wt-1 pH unit-1) (mean +/- SD). There was no relationship between beta mtitr and mean weekly running distance amongst spontaneously running rats, nor was beta mtitr any greater in these rats than in a group of sedentary control rats. Protein to wet wt ratio was 31% higher (P < 0.0001) in the superficial vastus muscle when compared with soleus muscle (22.04 +/- 3.74 vs. 16.77 +/- 3.00 mg protein, 100 mg wet wt muscle-1), but there was no relationship between protein to wet wt ratio and running distance. Initial muscle homogenate pH (pHi) 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 pHi in both soleus and superficial vastus than sedentary controls. There was an exponential relationship between weekly running distance and pHi in both the superficial vastus muscle (r = -0.86. P < 0.001) and the soleus muscle (r = -0.73, P < 0.01). Citrate synthase activity correlated with weekly running distance in superficial vastus muscle (r = 0.66, P < 0.01) but not in soleus muscle. The results confirm a higher beta mtitr 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 beta mtitr in mixed muscle (e.g. human vastus lateralis) should report fibre type composition.
authors.affiliation: Department of Physiology, University of Cape Town Medical School, South Africa.
authors.forename: A R
authors.initials: AR
authors.lastname: Weston
authors.forename: G R
authors.initials: GR
authors.lastname: Wilson
authors.forename: T D
authors.initials: TD
authors.lastname: Noakes
authors.forename: K H
authors.initials: KH
authors.lastname: Myburgh
mesh_terms: D000251:Adenosine Triphosphatases / Q000378:metabolism; D000818:Animals; D001835:Body Weight / Q000502:physiology; D002021:Buffers; D002950:Citrate (si)-Synthase / Q000378:metabolism; D003238:Connective Tissue / Q000378:metabolism; D006651:Histocytochemistry; D006863:Hydrogen-Ion Concentration; D018656:Muscle Fibers, Fast-Twitch / Q000502:physiology; D018657:Muscle Fibers, Slow-Twitch / Q000502:physiology; D009124:Muscle Proteins / Q000378:metabolism; D018482:Muscle, Skeletal / Q000201:enzymology / Q000378:metabolism* / Q000502:physiology; D010805:Physical Conditioning, Animal / Q000502:physiology; D005082:Physical Exertion / Q000502:physiology*; D051381:Rats
chemical_list: D002021:Buffers; D009124:Muscle Proteins; D002950:Citrate (si)-Synthase; D000251:Adenosine Triphosphatases