Creative Engineering Program, Graduate School of Engineering, Nagoya Institute of Technology, Gokiso-cho, Showa-ku, Nagoya, Aichi, 4668555, Japan.
Department of Electrical and Mechanical Engineering, Graduate School of Engineering, Nagoya Institute of Technology, Gokiso-cho, Showa-ku, Nagoya, Aichi, 4668555, Japan.
J Biol Phys. 2021 Sep;47(3):287-300. doi: 10.1007/s10867-021-09579-4. Epub 2021 Sep 13.
Vertebrate hearts have undergone marked morphological and structural changes to adapt to different environments and lifestyles as part of the evolutionary process. Amphibians were the first vertebrates to migrate to land. Transition from aquatic to terrestrial environments required the ability to circulate blood against the force of gravity. In this study, we investigated the passive mechanical properties and histology of the ventricles of three species of Anura (frogs and toads) from different habitats, Xenopus laevis (aquatic), Pelophylax nigromaculatus (semiaquatic), and Bufo japonicus formosus (terrestrial). Pressure-loading tests demonstrated stiffer ventricles of P. nigromaculatus and B. j. formosus compared X. laevis ventricles. Histological analysis revealed a remarkable difference in the structure of cardiac tissue: thickening of the compact myocardium layer of P. nigromaculatus and B. j. formosus and enrichment of the collagen fibers of B. j. formosus. The amount of collagen fibers differed among the species, as quantitatively confirmed by second-harmonic generation light microscopy. No significant difference was observed in cardiomyocytes isolated from each animal, and the sarcomere length was almost the same. The results indicate that the ventricles of Anura stiffen during adaptation to life on land.
脊椎动物的心脏在进化过程中发生了显著的形态和结构变化，以适应不同的环境和生活方式。两栖动物是第一批迁移到陆地的脊椎动物。从水生环境到陆地环境的转变需要能够对抗重力循环血液的能力。在这项研究中，我们研究了来自不同栖息地的三种蛙类（青蛙和蟾蜍）的心室的被动机械特性和组织学，它们是非洲爪蟾（水生）、黑斑蛙（半水生）和日本林蛙（陆生）。压力加载测试表明，与非洲爪蟾的心室相比，黑斑蛙和日本林蛙的心室更硬。组织学分析显示心脏组织结构有显著差异：黑斑蛙和日本林蛙的致密心肌层增厚，日本林蛙的胶原蛋白纤维丰富。通过二次谐波产生的共聚焦显微镜定量证实，不同物种的胶原蛋白纤维数量存在差异。从每种动物分离的心肌细胞没有观察到明显差异，肌节长度几乎相同。结果表明，在适应陆地生活的过程中，蛙类的心室变硬。
