Oxygen drives skeletal muscle remodeling in an amphibious fish out of water

Skeletal muscle remodeling in response to terrestrial acclimation improves the locomotor performance of some amphibious fishes on land, but the cue for this remodeling is unknown. We tested the hypothesis that muscle remodeling in the amphibious Kryptolebias marmoratus on land is driven by higher O2 availability in atmospheric air, and the alternative hypothesis that remodeling is induced by a different environmental or physiological condition that fish experience on land. Fish were acclimated to 28 days of air, or to aquatic hyperoxia, hypercapnia, hypoxia, elevated temperature or fasting conditions. Air, fasting and hyperoxic conditions increased (>25%) the size of oxidative fibers in K. marmoratus while hypoxia had the reverse effect (23% decrease). Surprisingly, hyperoxia acclimation also resulted in a transformation of the musculature to include large bands of oxidative-like muscle. Our results show that K. marmoratus is highly responsive to environmental O2 levels and capitalizes on O2- rich opportunities to enhance O2 utilization by skeletal muscle.

陆生驯化引发的骨骼肌重塑，可改善部分两栖鱼类的陆地运动表现，但该重塑的触发诱因仍未明确。本研究针对两栖鱼类斑纹隐小鳉（Kryptolebias marmoratus）提出两项对立假说：其一，其陆地骨骼肌重塑由大气中更高的氧气可用性驱动；其二，重塑由鱼类在陆地遭遇的其他独特环境或生理条件诱导。我们将实验鱼分别驯化28天，处理组包括空气暴露、水生高氧、高碳酸血症、低氧、高温及禁食状态。结果显示，空气暴露、禁食与高氧驯化均可使斑纹隐小鳉的氧化型肌纤维面积增加25%以上，而低氧驯化则产生相反效果（肌纤维面积降低23%）。出乎意料的是，高氧驯化还会导致肌肉组织发生重塑，形成大片类氧化型肌纤维束。本研究结果表明，斑纹隐小鳉对环境氧气水平具有高度响应性，并能借助富氧环境提升骨骼肌的氧气利用效率。