Gillis Todd E, Regan Matthew D, Cox Georgina K, Harter Till S, Brauner Colin J, Richards Jeff G, Farrell Anthony P
Department of Integrative Biology, University of Guelph, Guelph, ON, Canada N1G 2W1
Department of Zoology, University of British Columbia, Vancouver, BC, Canada V6T 1Z4.
J Exp Biol. 2015 Dec;218(Pt 23):3754-61. doi: 10.1242/jeb.125070. Epub 2015 Oct 20.
Pacific hagfish, Eptatretus stoutii, can recover from 36 h of anoxia at 10°C. Such anoxia tolerance demands the mobilization of anaerobic fuels and the removal of metabolic wastes--processes that require a functional heart. The purpose of this study was to measure the metabolic response of the excised, cannulated hagfish heart to anoxia using direct calorimetry. These experiments were coupled with measurements of cardiac pH and metabolite concentrations, at multiple time points, to monitor acid-base balance and anaerobic ATP production. We also exposed hagfish to anoxia to compare the in vitro responses of the excised hearts with the in vivo responses. The calorimetry results revealed a significant reduction in the rate of metabolic heat production over the first hour of anoxia exposure, and a recovery over the subsequent 6 h. This response is likely attributable to a rapid anoxia-induced depression of aerobic ATP-production pathways followed by an upregulation of anaerobic ATP-production pathways such that the ATP production rate was restored to that measured in normoxia. Glycogen-depletion measurements suggest that metabolic processes were initially supported by glycolysis but that an alternative fuel source was used to support the sustained rates of ATP production. The maintenance of intracellular pH during anoxia indicates a remarkable ability of the myocytes to buffer/regulate protons and thus protect cardiac function. Altogether, these results illustrate that the low metabolic demand of the hagfish heart allows for near-routine levels of cardiac metabolism to be supported anaerobically. This is probably a significant contributor to the hagfish's exceptional anoxia tolerance.
太平洋盲鳗（Eptatretus stoutii）能够在10°C的环境下从36小时的缺氧状态中恢复过来。这种缺氧耐受性需要调动无氧燃料并清除代谢废物，而这些过程都需要一个功能正常的心脏。本研究的目的是使用直接量热法测量离体插管盲鳗心脏对缺氧的代谢反应。这些实验还在多个时间点测量了心脏的pH值和代谢物浓度，以监测酸碱平衡和无氧ATP的产生。我们还让盲鳗暴露于缺氧环境中，以比较离体心脏的体外反应和体内反应。量热法结果显示，在缺氧暴露的第一个小时内，代谢产热速率显著降低，随后6小时恢复。这种反应可能归因于缺氧迅速导致有氧ATP产生途径的抑制，随后无氧ATP产生途径上调，从而使ATP产生速率恢复到常氧状态下测得的水平。糖原消耗测量表明，代谢过程最初由糖酵解支持，但随后使用了替代燃料来源来支持ATP的持续产生速率。缺氧期间细胞内pH值的维持表明心肌细胞具有显著的缓冲/调节质子的能力，从而保护心脏功能。总之，这些结果表明，盲鳗心脏的低代谢需求使得无氧状态下能够维持接近正常水平的心脏代谢。这可能是盲鳗具有非凡缺氧耐受性的一个重要因素。
