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

Abstract: 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.

摘要：针对温带鱼类的研究表明，心脏线粒体功能与支持心脏做功的能力是热耐受能力的重要决定因素。本研究验证了如下假说：与红血南极鱼种诺氏南极鱼（Notothenia coriiceps）相比，无血红蛋白南极冰鱼头带冰鱼（Chaenocephalus aceratus）较低的热耐受能力，与其心脏有氧代谢能力下降相关。我们对置于环境温度下或暴露于临界热极限（critical thermal maximum, CTmax）的实验动物心脏，定量测定了柠檬酸合酶（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、腺苷酸水平及线粒体蛋白质表达的变化。与头带冰鱼相比，在环境温度与临界热极限条件下，诺氏南极鱼心脏中的柠檬酸合酶活性、三磷酸腺苷（ATP）浓度与能量负荷均更高。尽管两种鱼类的线粒体状态3呼吸速率均未因临界热极限暴露而受损，但头带冰鱼的线粒体状态4呼吸速率（反映质子漏出情况）在临界热极限暴露后显著升高，而诺氏南极鱼未出现该变化。温度与物种的交互作用使得诺氏南极鱼体内抗氧化剂与有氧代谢酶水平上升，而头带冰鱼无此现象。综上，本研究结果支持前述假说，即头带冰鱼心脏较低的有氧代谢能力是其热耐受能力低下的重要原因。