Bicudo J E, Zerbinatti C V
Departamento de Fisiologia, Universidade de São Paulo, Brasil.
Braz J Med Biol Res. 1995 Nov-Dec;28(11-12):1139-45.
Hovering flight has been described as the most energetically expensive form of locomotion. Among the vertebrates, hummingbirds weighing only 1.5-20 g are the elite practitioners of this aerial art. Their flight muscles are, therefore, the most oxygen demanding locomotor muscles per unit tissue mass of all vertebrates. Tissue level functional and structural adaptations for oxygen transport are compared between hummingbirds and mammals in this paper. Hummingbirds present extreme structural adaptations in their flight muscles. Mitochondrial densities greater than 30% are observed in their pectoral muscles, and the surface area of the inner membrane of their mitochondria is twice that of mammals. This doubling of their mitochondrial oxidative capacity is accompanied by a proportional increase in the specific activity (per g tissue) of the mitochondrial manganese superoxide dismutase (SOD-Mn) in their flight muscles, thus indicating that oxygen toxicity is not a constraint in the aerobic performance of hummingbirds during hovering flight. Finally, the liver appears to play a major role in providing the necessary substrates for their high aerobic performance, and also in eliminating the oxygen free radicals formed during oxidative phosphorylation.
悬停飞行被认为是最耗费能量的运动形式。在脊椎动物中，体重仅1.5至20克的蜂鸟是这种空中技艺的佼佼者。因此，它们的飞行肌肉是所有脊椎动物中单位组织质量对氧气需求最大的运动肌肉。本文比较了蜂鸟和哺乳动物在组织水平上氧气运输的功能和结构适应性。蜂鸟的飞行肌肉呈现出极端的结构适应性。在它们的胸肌中观察到线粒体密度大于30%，并且其线粒体内膜的表面积是哺乳动物的两倍。它们线粒体氧化能力的这种加倍伴随着其飞行肌肉中线粒体锰超氧化物歧化酶（SOD-Mn）比活性（每克组织）的相应增加，这表明在悬停飞行期间氧气毒性并非蜂鸟有氧性能的限制因素。最后，肝脏似乎在为其高有氧性能提供必要底物以及消除氧化磷酸化过程中形成的氧自由基方面发挥着主要作用。
