DEHYDRATION TOLERANCE IN WOOD FROGS - A NEW PERSPECTIVE ON DEVELOPMENT OF AMPHIBIAN FREEZE TOLERANCE
DEHYDRATION TOLERANCE IN WOOD FROGS - A NEW PERSPECTIVE ON DEVELOPMENT OF AMPHIBIAN FREEZE TOLERANCE
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DOI：
10.1152/ajpregu.1993.265.6.r1324
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发表时间：
1993-12-01
影响因子：
--
通讯作者：
STOREY, KB
中科院分区：
文献类型：
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作者：
CHURCHILL, TA;STOREY, KB
林蛙 (Rana sylvatica) 在实验性脱水过程中能够耐受 50-60% 的身体水分流失。无论动物是冷冻（-2℃）还是未冷冻（1℃），未受保护的青蛙的失水率都是相同的，但当青蛙被冷冻在苔藓保护层下时，失水率会大大降低。未受保护的动物可能会在短短 7-9 天内脱水死亡；这表明选择保护良好且潮湿的冬眠地点对于冬季生存的重要性。事先脱水会影响青蛙的冷却和冷冻特性，降低过冷点和-2℃下24小时后形成的冰量，并与冷冻暴露协同作用，刺激冷冻保护剂的合成。对 5 摄氏度控制脱水效果的分析表明，仅体内水分含量的变化（不冻结）就会刺激肝糖原分解以及将高浓度的葡萄糖输出到血液和其他器官中。秋季采集的青蛙脱水至体内失水总量的 50%，其不同器官中的葡萄糖水平为 165-1,409 nmol/mg 蛋白质，与对照值相比增加了 9 至 313 倍，达到的最终水平与冷冻暴露诱导的水平非常相似。这些数据支持这样的观点，即自然耐冻性的各种适应可能源自两栖动物处理水胁迫的现有机制，并且细胞体积变化可能是触发和维持支持冷冻生存的分子适应（例如冷冻保护剂输出）所涉及的信号之一。
Wood frogs, Rana sylvatica, tolerate the loss of 50-60% of total body water during experimental dehydration. The rate of water loss for unprotected frogs is the same whether animals are frozen (at -2-degrees-C) or unfrozen (at 1-degrees-C) but is greatly reduced when frogs are frozen under a protective layer of moss. Dehydrational death could occur in as little as 7-9 days for unprotected animals; this indicates the importance for winter survival of selecting well-protected and damp hibernation sites. Prior dehydration affected the cooling and freezing properties of frogs, reducing supercooling point and the amount of ice formed after 24 h at -2-degrees-C and acting synergistically with freezing exposure in stimulating cryoprotectant synthesis. Analysis of the effects of controlled dehydration at 5-degrees-C showed that changes in body water content alone (without freezing) stimulated liver glycogenolysis and the export of high concentrations of glucose into blood and other organs. Autumn-collected frogs dehydrated to 50% of total body water lost showed glucose levels of 165-1,409 nmol/mg protein in different organs, increases of 9- to 313-fold compared with control values and reaching final levels very similar to those induced by freezing exposure. The data support the proposal that various adaptations for natural freeze tolerance may have been derived from preexisting mechanisms for dealing with water stress in amphibians and that cell volume change may be one of the signals involved in triggering and sustaining molecular adaptations (e.g., cryoprotectant output) that support freezing survival.