Reed J Z, Butler P J, Fedak M A
School of Biological Sciences, University of Birmingham, Edgbaston, UK.
J Exp Biol. 1994 Sep;194:33-46. doi: 10.1242/jeb.194.1.33.
It is not known precisely how marine mammals are able to maintain muscle function during active swimming in breath-hold dives, when ventilation stops and heart rate falls. Examination of muscle biochemistry and histochemistry can provide information on the relative importance of different metabolic pathways, the contractile potential of the muscle fibres, the oxygen storage capacity of the muscle and the capillary distribution in these animals. In this study, samples of locomotory muscle were taken from wild grey seals (Halichoerus grypus), harbour seals (Phoca vitulina) and Antarctic fur seals (Arctocephalus gazella); Wistar rat muscle was analysed for comparative purposes. Activities of citrate synthase and beta-hydroxyacyl CoA dehydrogenase were higher in the harbour seal muscle than in the grey seal muscle, suggesting that harbour seals have a greater aerobic capacity. Both phocid muscles had a greater reliance on fatty acid oxidation than the fur seal or rat muscles. The myoglobin data demonstrate that the grey seals have the highest oxygen storage capacity of the three pinniped species, which correlates with their greater diving ability. Myoglobin levels were higher in all three pinniped species than in the Wistar rat. The fibre type compositions suggest that the muscles from the fur seals have higher glycolytic capacities than those of the phocid seals [fur seal pectoralis, 7% slow-twitch oxidative fibres (SO), 25% fast-twitch oxidative glycolytic fibres (FOG), 68% fast-twitch glycolytic fibres (FG); grey seal 57% SO, 5% FOG, 38% FG; area per cents]. However, the pectoralis muscle of the fur seal, although the most glycolytic of the pinniped muscles studied, has the highest capillary density, which indicates a high capacity for fuel distribution. These results show that, while pinniped muscle has an increased oxygen storage potential compared with the muscle of a typical terrestrial mammal, there are no distinct adaptations for diving in the enzyme pathways or fibre type distributions of the pinniped muscle. However, the muscle characteristics of each species can be related to its diving behaviour and foraging strategy.
目前尚不清楚海洋哺乳动物在屏气潜水时积极游泳期间，当呼吸停止且心率下降时，是如何维持肌肉功能的。对肌肉生物化学和组织化学的研究可以提供有关不同代谢途径的相对重要性、肌纤维的收缩潜力、肌肉的氧储存能力以及这些动物体内毛细血管分布的信息。在本研究中，从野生灰海豹（Halichoerus grypus）、斑海豹（Phoca vitulina）和南极毛皮海狮（Arctocephalus gazella）身上采集了运动肌肉样本；为作比较分析了Wistar大鼠的肌肉。斑海豹肌肉中柠檬酸合酶和β-羟酰基辅酶A脱氢酶的活性高于灰海豹肌肉，这表明斑海豹具有更强的有氧代谢能力。两种海豹科动物的肌肉比毛皮海狮或大鼠的肌肉更依赖脂肪酸氧化。肌红蛋白数据表明，灰海豹在三种鳍脚类动物中具有最高的氧储存能力，这与其更强的潜水能力相关。所有三种鳍脚类动物的肌红蛋白水平都高于Wistar大鼠。纤维类型组成表明，毛皮海狮的肌肉比海豹科动物的肌肉具有更高的糖酵解能力[毛皮海狮胸肌，7%慢肌纤维氧化型（SO），25%快肌纤维氧化糖酵解型（FOG），68%快肌纤维糖酵解型（FG）；灰海豹57% SO，5% FOG，38% FG；面积百分比]。然而，毛皮海狮的胸肌虽然是所研究的鳍脚类动物肌肉中糖酵解能力最强的，但毛细血管密度最高，这表明其具有很高的燃料分配能力。这些结果表明，虽然鳍脚类动物的肌肉与典型陆地哺乳动物的肌肉相比具有更高的氧储存潜力，但在鳍脚类动物肌肉的酶途径或纤维类型分布方面，并没有明显的适应潜水的特征。然而，每个物种的肌肉特征都与其潜水行为和觅食策略相关。
