Basal Lamina: the Scaffold for Orderly Cell Replacement

To explore in detail the relationships between basal lamina (BL) and regenerating cells, we have studied the reconstruction of skeletal muscle fibers and their associated capillaries in portions of rat and rabbit skeletal muscles after injury with either freezing, ischemia, or in situ autografting. Each type of injury produces complete necrosis of cells. The BL, however, remains intact in the area of injury and maintains a "map" of the outline of the spatial relationships between muscle fibers and capillaries. Repopulation of the defect with new cells occurs primarily along the old BL. The spatial relationship between cells, as it existed before injury, is thus reestablished. This process appears to be aided by the ability of each category of regenerating cells to grow along the cell-supporting surface of its own BL. The regenerating cells of muscle fibers and capillaries frequently form a new layer of BL. It is of the usual thickness and is deposited primarily along the outer surfaces of plasma membranes in locations in which the new cells are separated from the old BL. Where an old layer of BL is present overlying a newly formed layer, the old layer may be retained or it may be removed. Removal of redundant BL is probably mediated by interstitial cells which embrace the outside surfaces of BL of regenerated skeletal muscle fibers and capillaries.