Pörtner H O
Alfred-Wegener-Institut für Polar- und Meeresforschung, Okophysiologie, Postfach 12 01 61, D-27515 Bremerhaven, Germany.
J Exp Biol. 2002 Aug;205(Pt 15):2217-30. doi: 10.1242/jeb.205.15.2217.
Polar, especially Antarctic, oceans host ectothermic fish and invertebrates characterized by low-to-moderate levels of motor activity; maximum performance is reduced compared with that in warmer habitats. The present review attempts to identify the trade-offs involved in adaptation to cold in the light of progress in the physiology of thermal tolerance. Recent evidence suggests that oxygen limitations and a decrease in aerobic scope are the first indications of tolerance limits at both low and high temperature extremes. The cold-induced reduction in aerobic capacity is compensated for at the cellular level by elevated mitochondrial densities, accompanied by molecular and membrane adjustments for the maintenance of muscle function. Particularly in the muscle of pelagic Antarctic fish, among notothenioids, the mitochondrial volume densities are among the highest known for vertebrates and are associated with cold compensation of aerobic metabolic pathways, a reduction in anaerobic scope, rapid recovery from exhaustive exercise and enhanced lipid stores as well as a preference for lipid catabolism characterized by high energy efficiency at high levels of ambient oxygen supply. Significant anaerobic capacity is still found at the very low end of the activity spectrum, e.g. among benthic eelpout (Zoarcideae). In contrast to the cold-adapted eurytherms of the Arctic, polar (especially Antarctic) stenotherms minimize standard metabolic rate and, as a precondition, the aerobic capacity per milligram of mitochondrial protein, thereby minimizing oxygen demand. Cost reductions are supported by the downregulation of the cost and flexibility of acid-base regulation. At maintained factorial scopes, the reduction in standard metabolic rate will cause net aerobic scope to be lower than in temperate species. Loss of contractile myofilaments and, thereby, force results from space constraints due to excessive mitochondrial proliferation. On a continuum between low and moderately high levels of muscular activity, polar fish have developed characteristics of aerobic metabolism equivalent to those of high-performance swimmers in warmer waters. However, they only reach low performance levels despite taking aerobic design to an extreme.
极地海洋，尤其是南极海洋，生存着变温鱼类和无脊椎动物，其特点是运动活动水平低至中等；与温暖栖息地的同类生物相比，它们的最大性能有所降低。本综述试图根据耐热生理学的进展，确定适应寒冷所涉及的权衡取舍。最近的证据表明，氧气限制和有氧范围的减小是低温和高温极端情况下耐受极限的最初迹象。低温导致的有氧能力下降在细胞水平上通过线粒体密度的升高得到补偿，同时伴随着分子和膜的调整以维持肌肉功能。特别是在南极远洋鱼类的肌肉中，在南极鱼亚目中，线粒体体积密度是脊椎动物中已知最高的之一，与有氧代谢途径的冷补偿、无氧范围的减小、力竭运动后的快速恢复、脂质储存的增加以及在高环境氧气供应水平下以高能效为特征的脂质分解偏好有关。在活动谱的极低端，例如在底栖绵鳚（绵鳚科）中，仍发现有显著的无氧能力。与北极适应寒冷的广温动物不同，极地（尤其是南极）狭温动物将标准代谢率降至最低，并以此为前提，将每毫克线粒体蛋白的有氧能力降至最低，从而使氧气需求最小化。酸碱调节成本和灵活性的下调有助于降低成本。在维持的系数范围内，标准代谢率的降低将导致净有氧范围低于温带物种。收缩性肌丝的丧失以及由此导致的力量丧失是由于线粒体过度增殖造成的空间限制所致。在低至中等高水平的肌肉活动连续体上，极地鱼类已经发展出了与温暖水域中高性能游泳者相当的有氧代谢特征。然而，尽管它们将有氧设计发挥到了极致，但它们的性能水平仍然很低。
