Jackson Donald C, Ultsch Gordon R
Department of Molecular Pharmacology, Physiology, and Biotechnology, Brown University, Providence, Rhode Island 02912, USA.
J Exp Zool A Ecol Genet Physiol. 2010 Jul 1;313(6):311-27. doi: 10.1002/jez.603.
Successful overwintering under ice by an air-breathing vertebrate requires either effective aquatic respiration if dissolved O(2) is available or the capacity for prolonged anaerobic metabolism if O(2) supplies are limiting. Frogs can remain aerobic for many weeks when submerged at low temperature, even at water PO(2) as low as 30 mmHg, but are unable to survive even 1 week in anoxic water. Fuel reserves of hibernating frogs limit aerobic submergence, whereas acidosis may limit anoxic submergence. Freshwater turtles can also satisfy all or most of their O(2) needs in well-aerated water at low temperature by aquatic respiration, but certain species, in particular painted and snapping turtles, can also survive for up to 4-5 months without O(2). Key adaptations of the painted turtles, and presumably snapping turtles, include metabolic depression and the exploitation of the shell and other bones to buffer lactic acid. As in frogs, glycogen and glucose are the only fuel sources during anoxia, and stores do not seem to be limiting in the painted turtle. Significant differences in anoxia tolerance exist among chelonian species that can be attributed, at least in part, to the magnitude of metabolic depression, the effectiveness of lactic acid buffering, and the size of glycogen stores.
对于用肺呼吸的脊椎动物来说，要在冰层下成功越冬，如果有溶解氧，就需要有效的水生呼吸；如果氧气供应有限，则需要具备长时间进行无氧代谢的能力。青蛙在低温下被淹没时，即使在水体氧分压低至30毫米汞柱的情况下，也能保持有氧状态数周，但在无氧水中甚至无法存活1周。冬眠青蛙的燃料储备限制了其有氧潜水时间，而酸中毒可能限制其无氧潜水时间。淡水龟在低温下的通气良好的水中，也能通过水生呼吸满足全部或大部分氧气需求，但某些物种，特别是锦龟和鳄龟，在没有氧气的情况下也能存活长达4至5个月。锦龟以及推测鳄龟的关键适应特征包括代谢抑制以及利用龟壳和其他骨骼来缓冲乳酸。与青蛙一样，糖原和葡萄糖是无氧状态下唯一的燃料来源，而且锦龟体内的储备似乎不存在限制。龟鳖类物种之间在耐缺氧能力上存在显著差异，这至少部分可归因于代谢抑制的程度、乳酸缓冲的效果以及糖原储备的大小。
