Fig. 5. Ultrastructure of muscle BLs. (A) In metal-stained ultrathin sections, myofiber membranes in wild-type mice are covered by a continuous BL, consisting of a transparent lamina rara adjacent to the plasma membrane (PM), a lamina densa (arrowheads) and an external reticular lamina that is rich in collagen fibrils (col). (B) In dy homozygotes, the BL is typically collapsed, with a thin lamina densa enmeshed with collagen fibrils adjacent to the sarcolemma. (C) In nmf417, myofiber BLs retain a layered structure, although the lamina densa is often thicker than normal. Scale bar: 200 nm.