Crossley Janna, Rippamonti Jessica D, Crossley Dane A, Dzialowski Edward M
Developmental Integrative Biology Group, Department of Biological Sciences, University of North Texas, Denton, TX, 76203, USA.
J Comp Physiol B. 2025 May 4. doi: 10.1007/s00360-025-01618-z.
Hypoxic conditions naturally occur in nests of egg laying reptiles including the American alligator, Alligator mississippiensis. The effects of developmental hypoxia have been delineated in several studies of this species, with changes in cardiovascular function persisting into juvenile life. However, several questions regarding the effects of developmental hypoxia remain. In this study we designed a series of experiments to quantify the effects of developmental hypoxia on permeabilized cardiac muscle fiber mitochondrial respiration, reactive oxygen species production, and response to acute anoxia in American alligators. Alligator eggs were incubated in 21% O (normoxia) or 10% O (hypoxia) at 30 °C beginning on day 14 of a 72-day incubation period through hatching. Animals were studied at two ages, at 90% of incubation and 1-year post hatching. Mitochondrial respiration and ROS production under leak and oxidative phosphorylation states were measured in permeabilized cardiac muscle fibers with high-resolution respirometry coupled with fluorometry. To examine the response of mitochondria to acute anoxia and subsequent reoxygenation, permeabilized cardiac muscle fibers were exposed to 20 min of anoxia, followed by reoxygenation during measurement of mitochondria respiration and ROS production. Hypoxic incubation resulted in a decrease in embryos mass which was maintained through the first year of juvenile life. Hypoxic incubation had no effect on cardiac mitochondria respiration or ROS production at either 90% of incubation or 1-year post hatching. After exposure to anoxia for 20 min, the rate of mitochondria respiration did not differ between the pre-anoxia respiration levels for all animals tested. There was no change in ROS production observed upon reoxygenation of the permeabilized cardiac muscle. Our results suggest that hypoxic incubation has little influence on cardiac myocyte mitochondrial physiology in the developing alligator and the cardiac mitochondria are resistant to acute bouts of anoxic exposure.
低氧环境自然存在于包括美国短吻鳄（密西西比鳄）在内的产卵爬行动物巢穴中。在对该物种的多项研究中，已经阐明了发育性低氧的影响，心血管功能的变化会持续到幼年时期。然而，关于发育性低氧影响的几个问题仍然存在。在本研究中，我们设计了一系列实验，以量化发育性低氧对美国短吻鳄透化心肌纤维线粒体呼吸、活性氧生成以及急性缺氧反应的影响。从72天孵化期的第14天开始直至孵化，将短吻鳄卵在30℃下于21%氧气（常氧）或10%氧气（低氧）环境中孵化。在两个年龄段对动物进行研究，分别是孵化期的90%时和孵化后1年。使用高分辨率呼吸测定法结合荧光测定法，测量透化心肌纤维在泄漏和氧化磷酸化状态下的线粒体呼吸和活性氧生成。为了检查线粒体对急性缺氧和随后复氧的反应，将透化心肌纤维暴露于20分钟的缺氧环境中，随后在测量线粒体呼吸和活性氧生成过程中进行复氧。低氧孵化导致胚胎质量下降，这种下降在幼年生活的第一年一直持续。低氧孵化对孵化期90%时或孵化后1年的心脏线粒体呼吸或活性氧生成均无影响。在暴露于缺氧20分钟后，所有测试动物的缺氧前呼吸水平与线粒体呼吸速率之间没有差异。透化心肌纤维复氧后，未观察到活性氧生成有变化。我们的结果表明，低氧孵化对发育中的短吻鳄心肌细胞线粒体生理学影响很小，并且心脏线粒体对急性缺氧暴露具有抗性。
