脊椎動物心筋膜系構造の比較研究

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  • Comparative Ultrastructure of Cell Membrane Specializations in Vertebrate Cardiac Muscles
  • セキツイ ドウブツ シンキン マクケイ コウゾウ ノ ヒカク ケンキュウ エイ

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The ultrastructure of ventricular cardiac muscles from representatives of all the vertebrate phyla is examined with the electron microscope using thin sections and freeze-fracture replicas. Contrary to the mammalian heart in which the width of the muscle fiber is usually over 10μm, and T-tubules and sarcoplasmic reticulum (SR) are well developed, non-mammalian cardiac muscles in general show small fiber diameter of less than 5μm, lack T-tubules, and reveal a wide variety in the degree of SR development. The rainbow trout and the lamprey, as well as the sparrow, reveal well-developed SR and numerous subsurface cisternae (SC) in proximity to Z line level. On the other hand, lizard and frog ventricles show poor development of SR and infrequent SC at A band level.<br>Nexus (gap junction) can be identified in all the vertebrate hearts examined by freeze-fracture technique. However, it is much smaller and more sparsely distributed in non-mammalian hearts than in mammals.<br>These morphological differences may imply different electrophysiological properties correlated with the small fiber diameter of the lower vertebrate cardiac muscles.

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