Journal of Electron Microscopy 51:183-194 (2002)
© 2002 Oxford University Press
Remodelling of capillary networks around muscle fibres in the extensor digitorum longus muscle of the normal aged rat
Departments of 1Anatomy and 2Orthopaedic Surgery, Ehime University School of Medicine, Shigenobu, Ehime 791-0295 and 3Department of Anatomy, Kumamoto University School of Medicine, Honjo, Kumamoto 860-0811, Japan
To whom correspondence should be addressed. E-mail: desaki{at}m.ehime-u.ac.jp
Structural changes of capillaries around muscle fibres following their degeneration and regeneration were further examined in the extensor digitorum longus muscle of the 24-month-old normal rat. Bundles of muscle fibres were divided into three types: muscle bundles consisting of large muscle fibres exclusively more than 35 µm in diameter (type 1), various-sized muscle fibres ranging from 10 to 60 µm in diameter (type 2) and only small muscle fibres 20–40 µm in diameter (type 3). The mean number of capillaries around a muscle fibre was extremely high in the type 3 muscle bundle (4.83) and much lower in the type 2 muscle bundle (2.72) compared with that in the type 1 muscle bundle (3.48). Capillaries in the type 1 muscle bundle were round or oval in shape and were of the continuous type. In the type 2 muscle bundle, capillaries around large degenerating muscle fibres showed an irregularly compressed shape and the scaffolds of basal laminae were often found around them, being a result of the destruction of capillaries. On the other hand, small-sized capillaries less than 5 µm in diameter, being possibly regenerating capillaries, were found around small (probably regenerating) muscle fibres and often had a small number (less than 10) of fenestrae. Capillaries in the type 3 muscle bundle, similar in shape and size to those in the type 1, frequently branched or joined, but some of them were partially destroyed. These findings suggest that capillaries degenerate and regenerate to remodel capillary networks around the muscle fibres following their degeneration and regeneration, and that to effectively supply oxygen and nutrients to regenerating muscle fibres, capillaries temporarily form fenestrae and then the capillary networks become dense by sprouts from the existing capillaries, but excess capillaries may be gradually destroyed following maturation of the muscle fibres.
Keywords capillary, endothelial cell, scaffold of basal lamina, fenestrae, degenerating and regenerating muscle fibres, 24-month-old rat, serial ultrathin sections
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