Seebacher Frank, Little Alexander G
School of Life and Environmental Sciences, University of SydneySydney, NSW, Australia.
Rosenstiel School of Marine and Atmospheric Science, The University of MiamiMiami, FL, United States.
Front Physiol. 2017 Aug 4;8:575. doi: 10.3389/fphys.2017.00575. eCollection 2017.
Endotherms regulate their core body temperature by adjusting metabolic heat production and insulation. Endothermic body temperatures are therefore relatively stable compared to external temperatures. The thermal sensitivity of biochemical reaction rates is thought to have co-evolved with body temperature regulation so that optimal reaction rates occur at the regulated body temperature. However, recent data show that core body temperatures even of non-torpid endotherms fluctuate considerably. Additionally, peripheral temperatures can be considerably lower and more variable than core body temperatures. Here we discuss whether published data support the hypothesis that thermal performance curves of physiological reaction rates are plastic so that performance is maintained despite variable body temperatures within active (non-torpid) endotherms, and we explore mechanisms that confer plasticity. There is evidence that thermal performance curves in tissues that experience thermal fluctuations can be plastic, although this question remains relatively unexplored for endotherms. Mechanisms that alter thermal responses locally at the tissue level include transient potential receptor ion channels (TRPV and TRPM) and the AMP-activated protein kinase (AMPK) both of which can influence metabolism and energy expenditure. Additionally, the thermal sensitivity of processes that cause post-transcriptional RNA degradation can promote the relative expression of cold-responsive genes. Endotherms can respond to environmental fluctuations similarly to ectotherms, and thermal plasticity complements core body temperature regulation to increase whole-organism performance. Thermal plasticity is ancestral to endothermic thermoregulation, but it has not lost its selective advantage so that modern endotherms are a physiological composite of ancestral ectothermic and derived endothermic traits.
恒温动物通过调节代谢产热和绝缘来维持其核心体温。因此，与外界温度相比，恒温动物的体温相对稳定。生化反应速率的热敏感性被认为与体温调节共同进化，从而使最佳反应速率在调节后的体温下出现。然而，最近的数据表明，即使是非蛰伏恒温动物的核心体温也会有很大波动。此外，外周温度可能比核心体温低得多且变化更大。在这里，我们讨论已发表的数据是否支持这样的假设，即生理反应速率的热性能曲线是可塑的，从而在活跃（非蛰伏）恒温动物体内体温变化的情况下仍能维持性能，并且我们探索赋予可塑性的机制。有证据表明，经历热波动的组织中的热性能曲线可能是可塑的，尽管对于恒温动物来说这个问题仍相对未被探索。在组织水平上局部改变热反应的机制包括瞬时电位受体离子通道（TRPV和TRPM）以及AMP激活的蛋白激酶（AMPK），这两者都可以影响代谢和能量消耗。此外，导致转录后RNA降解的过程的热敏感性可以促进冷响应基因的相对表达。恒温动物可以像变温动物一样对外界波动做出反应，热可塑性补充了核心体温调节以提高整个生物体的性能。热可塑性是恒温动物体温调节的祖先特征，但它并没有失去其选择优势，因此现代恒温动物是祖先变温动物和衍生恒温动物特征的生理复合体。
