Davis Randall W, Polasek Lori, Watson Rebecca, Fuson Amanda, Williams Terrie M, Kanatous Shane B
Department of Marine Biology, Texas A&M University, 5007 Avenue U, Galveston, TX 77551, USA.
Comp Biochem Physiol A Mol Integr Physiol. 2004 Jul;138(3):263-8. doi: 10.1016/j.cbpb.2004.05.003.
When aquatic reptiles, birds and mammals submerge, they typically exhibit a dive response in which breathing ceases, heart rate slows, and blood flow to peripheral tissues is reduced. The profound dive response that occurs during forced submergence sequesters blood oxygen for the brain and heart while allowing peripheral tissues to become anaerobic, thus protecting the animal from immediate asphyxiation. However, the decrease in peripheral blood flow is in direct conflict with the exercise response necessary for supporting muscle metabolism during submerged swimming. In free diving animals, a dive response still occurs, but it is less intense than during forced submergence, and whole-body metabolism remains aerobic. If blood oxygen is not sequestered for brain and heart metabolism during normal diving, then what is the purpose of the dive response? Here, we show that its primary role may be to regulate the degree of hypoxia in skeletal muscle so that blood and muscle oxygen stores can be efficiently used. Paradoxically, the muscles of diving vertebrates must become hypoxic to maximize aerobic dive duration. At the same time, morphological and enzymatic adaptations enhance intracellular oxygen diffusion at low partial pressures of oxygen. Optimizing the use of blood and muscle oxygen stores allows aquatic, air-breathing vertebrates to exercise for prolonged periods while holding their breath.
当水生爬行动物、鸟类和哺乳动物潜入水中时，它们通常会表现出一种潜水反应，即呼吸停止、心率减慢，并且流向外周组织的血液减少。在强制潜水过程中出现的深度潜水反应会将血液中的氧气留存给大脑和心脏，同时让外周组织进入无氧状态，从而保护动物免于立即窒息。然而，外周血流量的减少与在水下游泳时支持肌肉代谢所需的运动反应直接冲突。在自由潜水动物中，潜水反应仍然会发生，但比强制潜水时的强度要小，并且全身代谢仍保持有氧状态。如果在正常潜水过程中血液中的氧气没有留存用于大脑和心脏的代谢，那么潜水反应的目的是什么呢？在这里，我们表明其主要作用可能是调节骨骼肌中的缺氧程度，以便能够有效地利用血液和肌肉中的氧气储备。矛盾的是，潜水脊椎动物的肌肉必须处于缺氧状态才能使有氧潜水时间最大化。与此同时，形态学和酶学上的适应性变化会在低氧分压下增强细胞内的氧气扩散。优化血液和肌肉中氧气储备的利用，能使水生的、需呼吸空气的脊椎动物在屏住呼吸的情况下长时间运动。
