Reduced non-bicarbonate skeletal muscle buffering capacity in mice with the mini-muscle phenotype

Abstract

Muscle pH decreases during exercise, which may impair function. Endurance training typically reduces muscle buffering capacity as a result of changes in fiber-type composition, but existing comparisons of species that vary in activity level are ambiguous. We hypothesized that high-runner (HR) lines of mice from an experiment that breeds mice for voluntary wheel running would have altered muscle buffering capacity as compared with their non-selected control counterparts. We also expected that 6 days of wheel access, as used in the selection protocol, would reduce buffering capacity, especially for HR mice. Finally, we expected a subset of HR mice with the 'mini-muscle' phenotype to have relatively low buffering capacity as a result of fewer type IIb fibers. We tested non-bicarbonate buffering capacity of thigh muscles. Only HR mice expressing the mini-muscle phenotype had significantly reduced buffering capacity, females had lower buffering capacity than males, and wheel access had no significant effect.

Selectively breeding for high voluntary physical activity in female mice does not bestow inherent characteristics that resemble eccentric remodeling of the heart, but the mini-muscle phenotype does

“… 18 , 24 This “mini-muscle” phenotype is no longer present in the C line, is fixed in HR line 3, and is polymorphic in HR line 6. 15 , 29 , 30 Population-genetic modeling indicate that the mini-muscle trait was either neutral or under negative selection in the C lines, but favored in the HR lines. 18 Of the 63 mice included in this study, all 7 in HR line 3 had the mini-muscle phenotype and 1 of the 8 mice in HR line 6 had it ( n ​= ​55 normal, n ​= ​8 mini-muscle).…”