Prewitt J S, Freistroffer D V, Schreer J F, Hammill M O, Burns J M
Department of Biological Sciences, University of Alaska Anchorage, 3211 Providence Dr, Anchorage, AK 99508, USA.
J Comp Physiol B. 2010 Jun;180(5):757-66. doi: 10.1007/s00360-010-0448-z. Epub 2010 Feb 7.
Adult marine mammal muscles rely upon a suite of adaptations for sustained aerobic metabolism in the absence of freely available oxygen (O(2)). Although the importance of these adaptations for supporting aerobic diving patterns of adults is well understood, little is known about postnatal muscle development in young marine mammals. However, the typical pattern of vertebrate muscle development, and reduced tissue O(2) stores and diving ability of young marine mammals suggest that the physiological properties of harbor seal (Phoca vitulina) pup muscle will differ from those of adults. We examined myoglobin (Mb) concentration, and the activities of citrate synthase (CS), beta-hydroxyacyl coA dehydrogenase (HOAD), and lactate dehydrogenase (LDH) in muscle biopsies from harbor seal pups throughout the nursing period, and compared these biochemical parameters to those of adults. Pups had reduced O(2) carrying capacity ([Mb] 28-41% lower than adults) and reduced metabolically scaled catabolic enzyme activities (LDH/RMR 20-58% and CS/RMR 29-89% lower than adults), indicating that harbor seal pup muscles are biochemically immature at birth and weaning. This suggests that pup muscles do not have the ability to support either the aerobic or anaerobic performance of adult seals. This immaturity may contribute to the lower diving capacity and behavior in younger pups. In addition, the trends in myoglobin concentration and enzyme activity seen in this study appear to be developmental and/or exercise-driven responses that together work to produce the hypoxic endurance phenotype seen in adults, rather than allometric effects due to body size.
成年海洋哺乳动物的肌肉具备一系列适应性特征，以便在无法自由获取氧气（O₂）的情况下维持有氧代谢。尽管这些适应性特征对成年动物有氧潜水模式的重要性已为人熟知，但对于幼年海洋哺乳动物出生后的肌肉发育却知之甚少。然而，脊椎动物肌肉发育的典型模式，以及幼年海洋哺乳动物组织中氧气储备的减少和潜水能力的降低表明，港海豹（Phoca vitulina）幼崽肌肉的生理特性将与成年海豹不同。我们检测了港海豹幼崽在整个哺乳期肌肉活检样本中的肌红蛋白（Mb）浓度，以及柠檬酸合酶（CS）、β - 羟酰基辅酶A脱氢酶（HOAD）和乳酸脱氢酶（LDH）的活性，并将这些生化参数与成年海豹的进行了比较。幼崽的氧气携带能力降低（[Mb]比成年海豹低28 - 41%），代谢规模的分解代谢酶活性降低（LDH/RMR比成年海豹低20 - 58%，CS/RMR比成年海豹低29 - 89%），这表明港海豹幼崽的肌肉在出生和断奶时在生化方面尚未成熟。这表明幼崽的肌肉无法支持成年海豹的有氧或无氧运动表现。这种不成熟可能导致幼崽潜水能力较低以及行为受限。此外，本研究中观察到的肌红蛋白浓度和酶活性趋势似乎是发育和/或运动驱动的反应，它们共同作用产生了成年海豹所具有的低氧耐力表型，而不是由体型引起的异速生长效应。
