Storey K B, Mosser D D, Douglas D N, Grundy J E, Storey J M
Department of Biology, Carleton University, Ottawa, Ontario, Canada.
Braz J Med Biol Res. 1996 Mar;29(3):283-307.
Although alien to man, the ability to endure the freezing of extracellular body fluids during the winter has developed in several species of terrestrially hibernating frogs and turtles as well as in many species of insects and other invertebrates. Wood frogs, for example, can endure freezing for at least 2 weeks with no breathing, no heart beat or blood circulation, and with up to 65% of their total body water as ice. Our studies are providing a comprehensive view of the requirements for natural freezing survival and of the physical and metabolic protection that must be offered for effective cryopreservation of vertebrate organs. Molecular mechanisms of natural freeze tolerance in lower vertebrates include: 1) control over ice crystal growth in plasma by ice nucleating proteins, 2) the accumulation of low molecular weight cryoprotectants to minimize intracellular dehydration and stabilize macromolecular components, and 3) good ischemia tolerance by all organs that may include metabolic arrest mechanisms to reduce organ energy requirements while frozen. Cryomicroscopy of tissue slices and magnetic resonance imaging (MRI) of whole animals is revealing the natural mode of ice propagation through an organism. MRI has also revealed that thawing is non-uniform; core organs (with high cryoprotectant levels) melt first, facilitating the early resumption of heart beat and blood circulation. Studies of the production and actions of the natural cryoprotectant, glucose, in frogs have shown its importance in maintaining a critical minimum cell volume in frozen organs and new work on the metabolic effects of whole body dehydration in 3 species of frogs has indicated that adaptations supporting freeze tolerance grew out of mechanisms that deal with desiccation resistance in amphibians. Studies of the regulation of cryoprotectant glucose synthesis by wood frog liver have shown the role of protein kinases and of alpha and beta adrenergic receptors in regulating the glycemic response, and of changes in membrane glucose transporter proteins to facilitate cryoprotectant distribution.
尽管对人类而言很陌生，但在几种陆栖冬眠的青蛙、乌龟以及许多昆虫和其他无脊椎动物物种中，已经形成了在冬季忍受细胞外体液冻结的能力。例如，林蛙能够忍受至少两周的冻结状态，期间没有呼吸、心跳或血液循环，其全身水分的65%会结成冰。我们的研究正在全面了解自然冷冻存活的要求以及有效冷冻保存脊椎动物器官所需的物理和代谢保护。低等脊椎动物自然抗冻的分子机制包括：1）通过冰核蛋白控制血浆中冰晶的生长；2）积累低分子量的冷冻保护剂，以尽量减少细胞内脱水并稳定大分子成分；3）所有器官具有良好的缺血耐受性，这可能包括代谢停滞机制，以降低冷冻时器官的能量需求。组织切片的低温显微镜检查和对整个动物的磁共振成像（MRI）正在揭示冰在生物体内传播的自然模式。MRI还显示解冻是不均匀的；核心器官（冷冻保护剂水平高）先融化，这有助于心跳和血液循环的早期恢复。对青蛙体内天然冷冻保护剂葡萄糖的产生和作用的研究表明，它在维持冷冻器官中细胞的临界最小体积方面很重要，并且对三种青蛙全身脱水的代谢影响的新研究表明，支持抗冻的适应性是从应对两栖动物抗干燥的机制发展而来的。对林蛙肝脏中冷冻保护剂葡萄糖合成调节的研究表明，蛋白激酶以及α和β肾上腺素能受体在调节血糖反应中发挥作用，并且膜葡萄糖转运蛋白的变化有助于冷冻保护剂的分布。
