Maximum aerobic performance in lines of Mus selected for high wheel-running activity: effects of selection, oxygen availability and the mini-muscle phenotype.
We compared maximum aerobic capacity during forced exercise (VO2max) in hypoxia (PO2=14% O2), normoxia (21%) and hyperoxia (30%) of lines of house mice selectively bred for high voluntary wheel running (S lines) with their four unselected control (C) lines. We also tested for pleiotropic effects of the ;mighty mini-muscle' allele, a Mendelian recessive that causes a 50% reduction in hind limb muscle but a doubling of mass-specific aerobic enzyme activity, among other pleiotropic effects. VO2max of female mice was measured during forced exercise on a motorized treadmill enclosed in a metabolic chamber that allowed altered PO2. Individual variation in VO2max was highly repeatable within each PO2, and values were also significantly correlated across PO2. Analysis of covariance showed that S mice had higher body-mass-adjusted VO2max than C at all PO2, ranging from +10.7% in hypoxia to +20.8% in hyperoxia. VO2max of S lines increased practically linearly with PO2, whereas that of C lines plateaued from normoxia to hyperoxia, and respiratory exchange ratio (=CO2 production/VO2max) was lower for S lines. These results suggest that the physiological underpinnings of VO2max differ between the S and C lines. Apparently, at least in S lines, peripheral tissues may sustain higher rates of oxidative metabolism if central organs provide more O2. Although the existence of central limitations in S lines cannot be excluded based solely on the present data, we have previously reported that both S and C lines can attain considerably higher VO2max during cold exposure in a He-O2 atmosphere, suggesting that limitations on VO2max depend on interactions between the central and peripheral organs involved. In addition, mini-muscle individuals had higher VO2max than did those with normal muscles, suggesting that the former might have higher hypoxia tolerance. This would imply that the mini-muscle phenotype could be a good model to test how exercise performance and hypoxia tolerance could evolve in a correlated fashion, as previous researchers have suggested.
Rezende
Enrico L
EL
Department of Biology, University of California, Riverside, CA 92521, USA. enrico.rezende@ebd.csic.es
Garland
Theodore
T
Chappell
Mark A
MA
Malisch
Jessica L
JL
Gomes
Fernando R
FR
D000704:Analysis of Variance; D000818:Animals; D005075:Biological Evolution; D004734:Energy Metabolism / Q000502:physiology*; D005260:Female; D051379:Mice / Q000502:physiology*; D018482:Muscle, Skeletal / Q000033:anatomy & histology / Q000502:physiology*; D010101:Oxygen Consumption / Q000502:physiology*; D005082:Physical Exertion / Q000502:physiology*; D012641:Selection, Genetic