Maximal oxygen consumption in relation to subordinate traits in lines of house mice selectively bred for high voluntary wheel running

Maximal oxygen consumption in relation to subordinate traits in lines of house mice selectively bred for high voluntary wheel running. J Appl Physiol 101: 477-485, 2006. First published April 6, 2006; doi:10.1152/japplphysiol.00042.2006.-We studied relations between maximal O-2 consumption (VO2max) during forced exercise and subordinate traits associated with blood O-2 transport and cellular respiration in four lines of mice selectively bred for high voluntary wheel running (S lines) and their four nonselected control (C) lines. Previously, we reported VO2max of 59 females at three P-O2 (hypoxia = 14% O-2, normoxia = 21%, hyperoxia = 30%). Here, we test the hypothesis that variation in VO2max can be explained, in part, by hemoglobin concentration and PO2 necessary to obtain 50% O-2 saturation of Hb (an estimate of Hb affinity for O-2) of the blood as well as citrate synthase activity and myoglobin concentration of ventricles and gastrocnemius muscle. Statistical analyses controlled for body mass, compared S and C lines, and also considered effects of the mini-muscle phenotype (present only in S lines and resulting from a Mendelian recessive allele), which reduces hindlimb muscle mass while increasing muscle mass-specific aerobic capacity. Although S lines had higher VO2max than C, subordinate traits showed no statistical differences when the presence of the mini-muscle phenotype was controlled. However, subordinate traits did account for some of the individual variation in VO2 (max). Ventricle size was a positive predictor of VO2 max at all three PO2. Blood Hb concentration was a positive predictor of VO2 (max) in S lines but a negative predictor in C lines, indicating that the physiological underpinnings of VO2 (max) have been altered by selective breeding. Mice with the mini-muscle phenotype had enlarged ventricles, with higher mass-specific citrate synthase activity and myoglobin concentration, which may account for their higher VO2 max in hypoxia.