Sommer A M, Pörtner H O
Alfred-Wegener-Institute for Polar and Marine Research, Ecophysiology/Ecotoxicology, Columbusstrasse, 27568 Bremerhaven, Germany.
Physiol Biochem Zool. 2004 Mar-Apr;77(2):174-86. doi: 10.1086/381468.
Previous studies in marine ectotherms from a latitudinal cline have led to the hypothesis that eurythermal adaptation to low mean annual temperatures is energetically costly. To obtain more information on the trade-offs and with that the constraints of thermal adaptation, mitochondrial functions were studied in subpolar lugworms (Arenicola marina L.) adapted to summer cold at the White Sea and were compared with those in boreal specimens from the North Sea, either acclimatized to summer temperatures or to winter cold. During summer, a comparison of mitochondria from subpolar and boreal worms revealed higher succinate oxidation rates and reduced Arrhenius activation energies (Ea) in state 3 respiration at low temperatures, as well as higher proton leakage rates in subpolar lugworms. These differences reflect a higher aerobic capacity in subpolar worms, which is required to maintain motor activity at low but variable environmental temperatures--however, at the expense of an elevated metabolic rate. The lower activity of citrate synthase (CS) found in subpolar worms may indicate a shift in metabolic control within mitochondria. In contrast, acclimatization of boreal lugworms to winter conditions elicited elevated mitochondrial CS activities in parallel with enhanced mitochondrial respiration rates. With falling acclimation temperatures, the significant Arrhenius break temperature in state 3 respiration (11 degrees C) became insignificant (5 degrees C) or even disappeared (0 degrees C) at lower levels of Arrhenius activation energies in the cold, similar to a phenomenon known from hibernating vertebrates. The efficiency of aerobic energy production in winter mitochondria rose as proton leakage in relation to state 3 decreased with cold acclimation, indicated by higher respiratory control ratio values and increased adenosine diphosphate/oxygen (ADP/O) ratios. These transitions indicate reduced metabolic flexibility, possibly paralleled by a loss in aerobic scope and metabolic depression during winter cold. Accordingly, these patterns contrast those found in summer-active, cold-adapted eurytherms at high latitudes.
先前对来自纬度梯度的海洋变温动物的研究提出了这样一种假说，即对年均低温的广温性适应在能量方面代价高昂。为了获取更多关于权衡取舍以及热适应限制的信息，我们研究了适应白海夏季寒冷环境的亚极地沙蠋（Arenicola marina L.）的线粒体功能，并将其与来自北海的北方标本进行比较，这些北方标本要么适应夏季温度，要么适应冬季寒冷。在夏季，对亚极地和北方沙蠋的线粒体进行比较发现，在低温下状态3呼吸中，亚极地沙蠋的琥珀酸氧化速率更高，阿累尼乌斯活化能（Ea）更低，且质子泄漏率更高。这些差异反映出亚极地沙蠋具有更高的有氧能力，这是在低温但多变的环境温度下维持运动活性所必需的——然而，代价是代谢率升高。在亚极地沙蠋中发现的柠檬酸合酶（CS）活性较低，可能表明线粒体内代谢控制发生了转变。相比之下，北方沙蠋适应冬季条件会导致线粒体CS活性升高，同时线粒体呼吸速率增强。随着驯化温度降低，状态3呼吸中显著的阿累尼乌斯断点温度（11摄氏度）变得不显著（5摄氏度），甚至在低温下阿累尼乌斯活化能较低时消失（0摄氏度），这与冬眠脊椎动物中已知的现象类似。随着寒冷驯化，冬季线粒体中质子泄漏相对于状态3减少，有氧能量产生效率提高，这表现为更高的呼吸控制率值和增加的二磷酸腺苷/氧气（ADP/O）比值。这些转变表明代谢灵活性降低，可能伴随着冬季寒冷期间有氧范围的丧失和代谢抑制。因此，这些模式与在高纬度夏季活跃、适应寒冷的广温动物中发现的模式形成对比。
