Department of Biological Sciences, California State University, East Bay, Hayward, California, USA.
Department of Biology, Portland State University, Portland, Oregon.
Compr Physiol. 2015 Sep 20;5(4):1677-703. doi: 10.1002/cphy.c130032.
Activity metabolism is supported by phosphorylated reserves (adenosine triphosphate, creatine phosphate), glycolytic, and aerobic metabolism. Because there is no apparent variation between vertebrate groups in phosphorylated reserves or glycolytic potential of skeletal muscle, variation in maximal metabolic rate between major vertebrate groups represents selection operating on aerobic mechanisms. Maximal rates of oxygen consumption in vertebrates are supported by increased conductive and diffusive fluxes of oxygen from the environment to the mitochondria. Maximal CO2 efflux from the mitochondria to the environment must be matched to oxygen flux, or imbalances in pH will occur. Among vertebrates, there are a variety of modes of locomotion and vastly different rates of metabolism supported by a variety of cardiorespiratory architectures. However, interclass comparisons strongly implicate systemic oxygen transport as the rate-limiting step to maximal oxygen consumption for all vertebrate groups. The key evolutionary step that accounts for the approximately 10-fold increase in maximal oxygen flux in endotherms versus ectotherms appears to be maximal heart rate. Other variables such as ventilation, pulmonary/gill, and tissue diffusing capacity, have excess capacity and thus are not limiting to maximal oxygen consumption. During maximal activity, the ratio of ventilation to respiratory system blood flow is remarkably similar among vertebrates, and CO2 extraction efficiency increases while oxygen extraction efficiency decreases, suggesting that the respiratory system provides the largest resistance to maximal CO2 flux. Despite the large variation in modes of activity and rates of metabolism, maximal rates of oxygen and CO2 flux appear to be limited by the cardiovascular and respiratory systems, respectively.
活动代谢由磷酸化储备（三磷酸腺苷、磷酸肌酸）、糖酵解和有氧代谢支持。由于脊椎动物群体之间在磷酸化储备或骨骼肌糖酵解潜力方面没有明显的差异，主要脊椎动物群体之间最大代谢率的差异代表了对有氧机制的选择。脊椎动物的最大耗氧量由从环境到线粒体的氧气传导和扩散通量的增加来支持。线粒体到环境的最大 CO2 排放必须与氧气通量相匹配，否则 pH 值会失衡。在脊椎动物中，有各种各样的运动方式和由各种心肺结构支持的代谢率差异很大。然而，类间比较强烈暗示，全身氧气输送是所有脊椎动物群体最大耗氧量的限速步骤。导致内温动物与外温动物最大氧气通量增加约 10 倍的关键进化步骤似乎是最大心率。其他变量，如通气、肺/鳃和组织扩散能力，具有过剩的能力，因此不会限制最大氧气消耗。在最大活动期间，脊椎动物之间的通气与呼吸系统血流的比值非常相似，而二氧化碳提取效率增加，而氧气提取效率降低，这表明呼吸系统对最大二氧化碳通量提供最大的阻力。尽管活动方式和代谢率的变化很大，但最大氧气和二氧化碳通量似乎分别受到心血管系统和呼吸系统的限制。
