Meeting Abstract
Effective aerobic locomotion depends on adequate delivery of oxygen and an appropriate allocation of metabolic substrates. The pattern of metabolic substrate use during exercise follows a predictive pattern in lowland native mammals. We have found that in two highland lineages of mice (Phyllotis and Peromyscus) this fuel use pattern is shifted to a greater reliance on carbohydrates to power locomotion. However, there is variation between lineages and in different populations in the importance of phenotypic plasticity in the expression of this metabolic phenotype. Moreover, this metabolic phenotype during exercise is independent of running aerobic capacity but can also be independent of thermogenic capacity. For example, wild-caught mice from a highland population of deer mice Peromyscus maniculatus maintains higher maximum cold-induced oxygen consumption in hypoxia than lowland congenerics, but this is supported by high rates of lipid oxidation. This is reflected in the consistently higher activities of oxidative and fatty acid oxidation enzymes in the gastrocnemius of highland compared to lowlanders. In contrast, the activities of enzymes involved in glycolysis and exercise fuel use showed significant phenotypic plasticity in muscle with hypoxia acclimation in highland mice. This suggests that while a fixed trait in muscle aerobic capacity may reflect the stable low oxygen conditions at high altitude, muscle capacities for substrate oxidation may be more flexible to match appropriate substrate use with changing energetic demands. How shivering thermogenesis and locomotion potentially interact in the matching of muscle metabolic capacities to appropriate substrate use is unclear. Perhaps it is possible that shivering serves as “training” to ensure muscles have the capacity to support locomotion or visa-versa.
