Regeneration of skeletal muscle and changes of capillaries in mouse gastrocnemius muscle

Abstract

  Muscle fibers are larger than regular cells. This large size is unfavorable in the transfer of nutrients and waste because the surface area per unit volume in the cell decreases as the volume of the cell increases. Therefore, capillaries around the muscle fibers play an important role. In the process of muscle regeneration, nutrients and chemical substances are necessary for proliferation and differentiation. This report aims to clarify the changes in capillaries during the early regeneration of skeletal muscle and to establish simple and clear regeneration stages of skeletal muscle according to capillary changes.

  Mouse gastrocnemius muscle was injured with an 18G needle through the skin as an intramuscular injection without drugs. Paraffin sections were made over time after the injury and alkaline phosphatase staining was executed to detect the capillaries in the damaged tissue.

  Alkaline phosphatase-positive structures, endothelial cells of the capillary, were identified in the damaged tissue 1 hour and 8 hours after injury. However, these structures were not identified 24 hours after injury. Two days after injury, alkaline phosphatase-positive cells were identified again. After this, the alkaline phosphatase-positive region increased over time. It seems that the disappearance of capillaries at 24 hours after injury is the degradation of the capillaries, and the capillaries appearing again 2 days after injury are newly grown. Depending on the capillary changes, we established that the regeneration of skeletal muscle is composed of 4 stages.

  These stages provide a useful standard for analyzing the regeneration process in skeletal muscle.