Scott Graham R, Richards Jeffrey G, Milsom William K
Department of Zoology, University of British Columbia, Vancouver, British Columbia, Canada.
Am J Physiol Regul Integr Comp Physiol. 2009 Oct;297(4):R1066-74. doi: 10.1152/ajpregu.00241.2009. Epub 2009 Aug 5.
Bar-headed geese fly at altitudes of up to 9,000 m on their biannual migration over the Himalayas. To determine whether the flight muscle of this species has evolved to facilitate exercise at high altitude, we compared the respiratory properties of permeabilized muscle fibers from bar-headed geese and several low-altitude waterfowl species. Respiratory capacities were assessed for maximal ADP stimulation (with single or multiple inputs to the electron transport system) and cytochrome oxidase excess capacity (with an exogenous electron donor) and were generally 20-40% higher in bar-headed geese when creatine was present. When respiration rates were extrapolated to the entire pectoral muscle mass, bar-headed geese had a higher mass-specific aerobic capacity. This may represent a surplus capacity that counteracts the depressive effects of hypoxia on mitochondrial respiration. However, there were no differences in activity for mitochondrial or glycolytic enzymes measured in homogenized muscle. The [ADP] leading to half-maximal stimulation (K(m)) was approximately twofold higher in bar-headed geese (10 vs. 4-6 microM), and, while creatine reduced K(m) by 30% in this species, it had no effect on K(m) in low-altitude birds. Mitochondrial creatine kinase may therefore contribute to the regulation of oxidative phosphorylation in flight muscle of bar-headed geese, which could promote efficient coupling of ATP supply and demand. However, this was not based on differences in creatine kinase activity in isolated mitochondria or homogenized muscle. The unique differences in bar-headed geese existed without prior exercise or hypoxia exposure and were not a result of phylogenetic history, and may, therefore, be important evolutionary specializations for high-altitude flight.
斑头雁在每年两次飞越喜马拉雅山脉的迁徙过程中，能在高达9000米的海拔高度飞行。为了确定该物种的飞行肌肉是否已经进化以利于在高海拔地区运动，我们比较了斑头雁和几种低海拔水禽物种的透化肌纤维的呼吸特性。评估了最大ADP刺激（对电子传递系统进行单次或多次输入）和细胞色素氧化酶过量能力（使用外源电子供体）时的呼吸能力，当存在肌酸时，斑头雁的呼吸能力通常高出20%-40%。当将呼吸速率外推至整个胸肌质量时，斑头雁具有更高的质量特异性有氧能力。这可能代表一种过剩能力，可抵消缺氧对线粒体呼吸的抑制作用。然而，在匀浆肌肉中测量的线粒体或糖酵解酶的活性没有差异。导致半最大刺激的[ADP]（K(m)）在斑头雁中大约高出两倍（10对4-6 microM），虽然肌酸使该物种的K(m)降低了30%，但对低海拔鸟类的K(m)没有影响。因此，线粒体肌酸激酶可能有助于调节斑头雁飞行肌肉中的氧化磷酸化，这可以促进ATP供需的有效耦合。然而，这并非基于分离线粒体或匀浆肌肉中肌酸激酶活性的差异。斑头雁的独特差异在没有预先运动或缺氧暴露的情况下就已存在，也不是系统发育历史的结果，因此可能是高海拔飞行重要的进化特化。
