Johnston I A, Dunn J
Department of Physiology and Pharmacology, University of St Andrews, Scotland.
Symp Soc Exp Biol. 1987;41:67-93.
As body temperature decreases, changes in the physical chemistry of the cell produce a reduction in metabolic activity. In temperate fish, cold water temperatures either lead to dormancy or else trigger a range of homeostatic responses which serve to offset the passive effects of reduced temperature. Compensatory adjustments to temperature occur with time courses ranging from less than a second to more than a month. Although swimming performance may increase with cold-acclimation, active metabolic rate remains significantly below that for warm-acclimated fish. Compensatory and dormancy responses are not mutually exclusive and sometimes occur in the same species depending on the temperature. Cold-acclimation results in significant increases in the density of mitochondria and capillaries in skeletal muscle. This serves to reduce diffusion distances and increase the capacity for aerobic ATP production relative to fish acutely exposed to low temperature. There is evidence that cold acclimation has differential effects on the synthesis and degradation rates of mitochondrial proteins leading to a net increase in their concentration. In contrast, the activities of enzymes associated with glycolysis and phosphocreatine hydrolysis show no consistent changes with thermal acclimation suggesting that flux through these pathways is modulated by factors other than enzyme concentration. Higher mitochondrial densities have also been reported for the liver, brain and gill tissue of cold compared with warm acclimated fish. In spite of their increased concentration, the activities of aerobic enzymes remain much lower at cold than warm temperatures. Acclimation temperature affects hepatosomatic index, the concentration of energy reserves, and the relative importance of glucose and fatty acid catabolism in liver. The fraction of glucose oxidized by the hexose monophosphate shunt (HMPS) pathway also increases with cold acclimation in some species. It is likely that many of the changes in liver metabolism with temperature acclimation reflect associated changes in feeding behaviour and/or diet, and other energetic demands (e.g. gametogenesis). Possible mechanisms underlying alterations in pathway utilization with temperature acclimation are discussed. They include changes in factors influencing enzyme structure and activity (e.g. pH, substrate/modulator concentrations, phosphorylation state, membrane composition), and effects of temperature on gene expression.
随着体温下降，细胞物理化学性质的变化会导致代谢活动降低。在温带鱼类中，冷水温度要么导致休眠，要么引发一系列稳态反应，以抵消温度降低的被动影响。对温度的补偿性调整发生的时间范围从不到一秒到超过一个月不等。尽管游泳能力可能会随着冷适应而提高，但活跃代谢率仍显著低于暖适应鱼类。补偿性反应和休眠反应并非相互排斥，有时会因温度不同而在同一物种中同时出现。冷适应会导致骨骼肌中线粒体和毛细血管密度显著增加。这有助于缩短扩散距离，并相对于急性暴露于低温的鱼类提高有氧ATP生成能力。有证据表明，冷适应对线粒体蛋白质的合成和降解速率有不同影响，导致其浓度净增加。相比之下，与糖酵解和磷酸肌酸水解相关的酶活性在热适应过程中没有一致变化，这表明这些途径的通量受酶浓度以外的因素调节。与暖适应鱼类相比，冷适应鱼类的肝脏、大脑和鳃组织中线粒体密度也更高。尽管其浓度有所增加，但有氧酶的活性在低温下仍远低于高温。适应温度会影响肝体指数、能量储备浓度以及肝脏中葡萄糖和脂肪酸分解代谢的相对重要性。在某些物种中，通过己糖磷酸旁路（HMPS）途径氧化的葡萄糖比例也会随着冷适应而增加。肝脏代谢随温度适应的许多变化可能反映了摄食行为和/或饮食以及其他能量需求（如配子发生）的相关变化。文中讨论了温度适应导致途径利用改变的潜在机制。它们包括影响酶结构和活性的因素变化（如pH、底物/调节剂浓度、磷酸化状态、膜组成）以及温度对基因表达的影响。
