Hardewig I, Van Dijk P L, Portner H O
Alfred Wegener Institute for Polar and Marine Research, Biologie I/Ecophysiologie, 27568 Bremerhaven, Germany.
Am J Physiol. 1998 Jun;274(6):R1789-96. doi: 10.1152/ajpregu.1998.274.6.R1789.
Earlier work on Notothenioids led to the hypothesis that a reduced glycolytic capacity is a general adaptation to low temperatures in Antarctic fish. In our study this hypothesis was reinvestigated by comparing changes in the metabolic status of the white musculature in two related zoarcid species, the stenothermal Antarctic eelpout Pachycara brachycephalum and the eurythermal Zoarces viviparus during exercise and subsequent recovery at 0 degreesC. In both species, strenuous exercise caused a similar increase in white muscle lactate, a drop in intracellular pH (pHi) by about 0.5 pH units, and a 90% depletion of phosphocreatine. This is the first study on Antarctic fish that shows an increase in white muscle lactate concentrations. Thus the hypothesis that a reduced importance of the glycolytic pathway is characteristic for cold-adapted polar fish cannot hold. The recovery process, especially the clearance of white muscle lactate, is significantly faster in the Antarctic than in temperate eelpout. Based on metabolite data, we calculated that during the first hour of recovery aerobic metabolism is increased 6.6-fold compared with resting rates in P. brachycephalum vs. an only 2.9-fold increase in Z. viviparus. This strong stimulation of aerobic metabolism despite low temperatures may be caused by a pronounced increase of free ADP levels, in the context of higher levels of pHi and ATP, which is observed in the Antarctic species. Although basal metabolic rates are identical in both species, the comparison of metabolic rates during situations of high-energy turnover reveals that the stenothermal P. brachycephalum shows a higher degree of metabolic cold compensation than the eurythermal Z. viviparus. Muscular fatigue after escape swimming may be caused by a drop of the free energy change of ATP hydrolysis, which is shown to fall below critical levels for cellular ATPases in exhausted animals of both species.
早期对南极鱼亚目的研究提出了一个假说，即糖酵解能力的降低是南极鱼类对低温的一种普遍适应性。在我们的研究中，通过比较两种相关的绵鳚科物种——狭温性的南极长头突吻鳕和广温性的胎生绵鳚——在0摄氏度下运动及随后恢复过程中白色肌肉代谢状态的变化，对这一假说进行了重新研究。在这两个物种中，剧烈运动都会导致白色肌肉乳酸含量类似地增加，细胞内pH值（pHi）下降约0.5个pH单位，以及磷酸肌酸消耗90%。这是首次关于南极鱼类的研究表明白色肌肉乳酸浓度会增加。因此，认为糖酵解途径重要性降低是适应寒冷的极地鱼类特征的假说不成立。恢复过程，尤其是白色肌肉乳酸的清除，在南极鱼类中比在温带绵鳚中要快得多。根据代谢物数据，我们计算出在恢复的第一个小时内，与静息速率相比，长头突吻鳕的有氧代谢增加了6.6倍，而胎生绵鳚仅增加了2.9倍。尽管温度很低，但这种对有氧代谢的强烈刺激可能是由游离ADP水平的显著增加引起的，在南极物种中观察到更高水平的pHi和ATP。虽然这两个物种的基础代谢率相同，但在高能量转换情况下代谢率的比较表明，狭温性的长头突吻鳕比广温性的胎生绵鳚表现出更高程度的代谢冷补偿。逃避游泳后的肌肉疲劳可能是由ATP水解自由能变化的下降引起的，在这两个物种精疲力竭的动物中，ATP水解自由能变化已降至细胞ATP酶的临界水平以下。
