Feeding effects on liver mitochondrial bioenergetics of Boa constrictor (Serpentes: Boidae)

Snakes are interesting examples of overcoming energy metabolism challenges as many species can endure long periods without feeding, and their eventual meals are of reasonably large sizes, thus exhibiting dual extreme adaptations. Consequently, metabolic rate increases considerably to attend to the energetic demand of digestion, absorption and, protein synthesis. These animals should be adapted to transition from these two opposite states of energy fairly quickly, and therefore we investigated mitochondrial function plasticity in these states. Herein we compared liver mitochondrial bioenergetics of the boid snake Boa constrictor during fasting and after meal intake. We fasted the snakes for 60 days, then we fed a subgroup with 30% of their body size and evaluated their maximum postprandial response. We measured liver respiration rates from permeabilized tissue and isolated mitochondria, and from isolated mitochondria, we also measured Ca2+ retention capacity, the release of H2O2, and NAD(P) redox state. Mitochondrial respiration rates were maximized after feeding, reaching until 60% increase from fasting levels when energized with complex I-linked substrates. Interestingly, fasting and fed snakes exhibited similar respiratory control ratios and citrate synthase activity. Furthermore, we found no differences in Ca2+ retention capacity, indicating no increase in susceptibility to mitochondrial permeability transition pore (PTP), or redox state of NAD(P), although fed animals exhibited increases in the release of H2O2. Thus, we conclude that liver mitochondria from B. constrictor snakes increase the maintenance costs during the postprandial period and quickly improve the mitochondrial bioenergetics capacity without compromising the redox balance.

蛇类是克服能量代谢挑战的典型研究范例：诸多蛇类物种能够耐受长期禁食，且单次摄食体量相对较大，由此呈现出双重极端适应性特征。为满足消化、吸收与蛋白质合成的能量需求，其代谢速率会显著提升。这类动物需要能够快速在这两种截然相反的能量代谢状态间切换，因此本研究针对这两种状态下的线粒体功能可塑性展开探究。本研究以蚺科蛇类红尾蚺（Boa constrictor）为对象，对比其禁食期与进食后的肝脏线粒体生物能学（mitochondrial bioenergetics）特征。我们将受试蛇禁食60天，随后选取亚组投喂其体重30%的食物，并评估其餐后最大代谢响应。我们分别从透化肝脏组织（permeabilized tissue）与分离线粒体（isolated mitochondria）中检测呼吸速率；针对分离线粒体，还测定了其钙保留能力（Ca²⁺ retention capacity）、过氧化氢（H₂O₂）释放量以及NAD(P)氧化还原状态（NAD(P) redox state）。当使用复合物I（complex I）关联底物供能时，进食后的线粒体呼吸速率达到峰值，较禁食状态提升可达60%。值得注意的是，禁食组与进食组的蛇类展现出相似的呼吸控制比率（respiratory control ratio, RCR）与柠檬酸合酶（citrate synthase）活性。此外，两组在钙保留能力上无显著差异，表明进食并未提升线粒体通透性转换孔（mitochondrial permeability transition pore, PTP）的开放敏感性，NAD(P)氧化还原状态也未发生明显变化；不过进食组的过氧化氢释放量确实有所升高。综上，我们得出结论：红尾蚺的肝脏线粒体在餐后阶段会提升维持成本，并在不破坏氧化还原平衡的前提下，快速优化线粒体生物能学性能。