Kanatous S B, Hawke T J, Trumble S J, Pearson L E, Watson R R, Garry D J, Williams T M, Davis R W
Department of Biology, Colorado State University, Fort Collins, CO 80523-1878, USA.
J Exp Biol. 2008 Aug;211(Pt 16):2559-65. doi: 10.1242/jeb.018119.
Our objective was to determine the ontogenetic changes in the skeletal muscles of Weddell seals that transform a non-diving pup into an elite diving adult. Muscle biopsies were collected from pups, juveniles and adults and analyzed for changes in fiber type, mitochondrial density, myoglobin concentrations and aerobic, lipolytic and anaerobic enzyme activities. The fiber type results demonstrated a decrease in slow-twitch oxidative (Type I) fibers and a significant increase in fast-twitch oxidative (Type IIA) fibers as the animals mature. In addition, the volume density of mitochondria and the activity of lipolytic enzymes significantly decreased as the seals matured. To our knowledge, this is the first quantitative account describing a decrease in aerobic fibers shifting towards an increase in fast-twitch oxidative fibers with a significant decrease in mitochondrial density as animals mature. These differences in the muscle physiology of Weddell seals are potentially due to their three very distinct stages of life history: non-diving pup, novice diving juvenile, and elite deep diving adult. During the first few weeks of life, pups are a non-diving terrestrial mammal that must rely on lanugo (natal fur) for thermoregulation in the harsh conditions of Antarctica. The increased aerobic capacity of pups, associated with increased mitochondrial volumes, acts to provide additional thermogenesis. As these future elite divers mature, their skeletal muscles transform to a more sedentary state in order to maintain the low levels of aerobic metabolism associated with long-duration diving.
我们的目标是确定威德尔海豹骨骼肌的个体发育变化，这些变化将一只不会潜水的幼崽转变为一名优秀的成年潜水者。从幼崽、幼年海豹和成年海豹身上采集肌肉活检样本，并分析纤维类型、线粒体密度、肌红蛋白浓度以及有氧、脂解和无氧酶活性的变化。纤维类型的结果表明，随着动物的成熟，慢肌氧化型（I型）纤维减少，快肌氧化型（IIA型）纤维显著增加。此外，随着海豹的成熟，线粒体的体积密度和脂解酶的活性显著降低。据我们所知，这是首次对有氧纤维减少、向快肌氧化纤维增加转变以及随着动物成熟线粒体密度显著降低进行定量描述。威德尔海豹肌肉生理学的这些差异可能归因于它们生命历程中的三个非常不同的阶段：不会潜水的幼崽、初涉潜水的幼年海豹和优秀的深潜成年海豹。在生命的最初几周，幼崽是一种不会潜水的陆生哺乳动物，在南极恶劣的环境中必须依靠胎毛进行体温调节。幼崽有氧能力的增强与线粒体体积的增加有关，这有助于提供额外的产热。随着这些未来的优秀潜水者的成熟，它们的骨骼肌转变为更久坐的状态，以维持与长时间潜水相关的低水平有氧代谢。
