Cardiac metabolism in Antarctic fishes in response to an acute increase in temperature

Studies in temperate fishes provide evidence that cardiac mitochondrial function and the capacity to fuel cardiac work contribute to thermal tolerance. Here, we tested the hypothesis that decreased cardiac aerobic metabolic capacity contributes to the lower thermal tolerance of the haemoglobinless Antarctic icefish, Chaenocephalus aceratus, compared with that of the red-blooded Antarctic species, Notothenia coriiceps. Maximal activities of citrate synthase (CS) and lactate dehydrogenase (LDH), respiration rates of isolated mitochondria, adenylate levels and changes in mitochondrial protein expression were quantified from hearts of animals held at ambient temperature or exposed to their critical thermal maximum (CTmax). Compared with C. aceratus, activity of CS, ATP concentration and energy charge were higher in hearts of N. coriiceps at ambient temperature and CTmax While state 3 mitochondrial respiration rates were not impaired by exposure to CTmax in either species, state 4 rates, indicative of proton leakage, increased following exposure to CTmax in C. aceratus but not N. coriiceps The interactive effect of temperature and species resulted in an increase in antioxidants and aerobic metabolic enzymes in N. coriiceps but not in C. aceratus Together, our results support the hypothesis that the lower aerobic metabolic capacity of C. aceratus hearts contributes to its low thermal tolerance.

针对温带鱼类的研究表明，心脏线粒体功能及为心脏做功供能的能力，是影响热耐受能力的关键因素。本研究旨在验证下述假说：与红细胞丰富的南极物种科氏南极鱼（Notothenia coriiceps）相比，无血红蛋白的南极冰鱼（Chaenocephalus aceratus）较低的心脏有氧代谢能力，是其热耐受能力更弱的原因。本研究对置于环境温度或临界热最大值（critical thermal maximum, CTmax）条件下的受试动物心脏样本，定量检测了以下指标：柠檬酸合酶（citrate synthase, CS）与乳酸脱氢酶（lactate dehydrogenase, LDH）的最大活性、分离线粒体的呼吸速率、腺苷酸水平，以及线粒体蛋白质表达的变化。与南极冰鱼（Chaenocephalus aceratus）相比，在环境温度及临界热最大值条件下，科氏南极鱼（Notothenia coriiceps）心脏中的柠檬酸合酶活性、ATP浓度及能量负荷均显著更高。尽管两种鱼类的线粒体状态3呼吸速率均未因临界热最大值暴露而受到损伤，但代表质子泄漏的线粒体状态4呼吸速率，在南极冰鱼中于临界热最大值暴露后出现升高，而科氏南极鱼则无此变化。温度与物种的交互作用使得科氏南极鱼体内的抗氧化物质及有氧代谢酶水平升高，而南极冰鱼未出现该变化。综合来看，本研究结果支持前述假说：南极冰鱼心脏较低的有氧代谢能力，是其热耐受能力较弱的原因。