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首页> 外文期刊>Journal of Comparative Physiology B: Biochemical, Systemic, and Environmental Physiology >Urea-induced hypometabolism in the hibernating wood frog (Rana sylvatica) is not reflected in isolated mitochondria
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Urea-induced hypometabolism in the hibernating wood frog (Rana sylvatica) is not reflected in isolated mitochondria

机译：冬眠的青蛙（尿蛙）中尿素引起的低代谢没有反映在孤立的线粒体中

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摘要

It has long been speculated that urea accumulated during seasonal dormancy contributes to metabolic depression. Recent work suggests urea can indeed act as a metabolic depressant during dormancy in a number of taxonomically diverse species of ectotherms. The mechanisms by which urea exerts its hypometabolic effect are unknown, but potentially stem from inhibition of mitochondrial respiration. We isolated mitochondria from Rana sylvatica skeletal muscle, an organ that is metabolically responsive to urea, and measured respiration rates in the absence or presence of 80 mmol l−1 urea in the respiration medium. Because the effect of urea may be influenced by the intracellular milieu, in these experiments we varied substrate (pyruvate or palmitoylcarnitine), temperature (4, 10, or 15°C), and pH (6.8 or 7.4). Oxygen consumption of control and urea-treated mitochondria was sensitive to each of these variables, but neither state 3 nor state 4 respiration was reduced by urea treatment and, to the contrary, urea treatment slightly increased state 4 respiration at higher test temperatures. Although we did not test the efficacy of other incubation times or urea concentrations, the outcome of our experiment intimates that the urea-induced hypometabolism observed in hibernating R. sylvatica results from inhibition of energy-utilizing processes elsewhere in the cell, rather than a direct inhibition of mitochondrial respiration. Future investigation into urea’s effects on non-mitochondrial metabolic pathways is necessary to uncover the mechanisms by which urea depresses metabolic rate.
机译：长期以来一直推测季节性休眠期间积累的尿素会导致代谢抑制。最近的工作表明，尿素确实可以在许多分类学上不同的外热物种中在休眠期间充当代谢抑制剂。尿素发挥其低代谢作用的机制尚不清楚，但可能源于线粒体呼吸的抑制。我们从林蛙骨骼肌中分离出线粒体，该骨骼肌对尿素具有代谢反应，并在呼吸介质中不存在或存在80 mmol lsup-1尿素的情况下测量呼吸速率。由于尿素的作用可能受细胞内环境的影响，因此在这些实验中，我们改变了底物（丙酮酸或棕榈酰肉碱），温度（4、10或15°C）和pH（6.8或7.4）。对照和尿素处理的线粒体的耗氧量对这些变量均敏感，但是在较高的测试温度下，尿素处理不会降低状态3和状态4的呼吸，相反，尿素处理会稍微增加状态4的呼吸。尽管我们没有测试其他温育时间或尿素浓度的功效，但我们的实验结果表明，冬眠紫苏中观察到的尿素诱导的低代谢是由于抑制了细胞其他部位的能量利用过程，而不是直接的抑制线粒体呼吸。有必要对尿素对非线粒体代谢途径的影响进行进一步研究，以揭示尿素降低代谢率的机制。

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