Fig. 2.

Ultrastructural studies of TA muscles lacking desmin, K19, or both proteins. Micrographs show representative transmission electron microscopic images of longitudinal sections of TA muscles from WT (A), K19−/− (B), desmin−/− (C), and DKO (D) mice. Scale bar in D applies to A–D (0.5 μm). E: compared with WT muscles, all 3 mutants showed a significant increase in the distance between the outermost myofibrils and the sarcolemma (Z line to membrane distance), with the largest in K19−/− muscles. The absence of desmin in the DKO muscle reduces this distance to a value identical to that seen in desmin−/− muscle. F: sarcomere alignment was determined by the horizontal distance from 1 Z line to the Z line in an adjacent myofibril (Z line to Z line distance). The sarcomeres were not significantly displaced in K19−/− compared with WT muscles, but the displacement increased significantly in the desmin−/− and was greatest in DKO muscles. *P < 0.001. G: quantitation of mitochondria under sarcolemma. The fraction of cytoplasmic surface of the sarcolemmal membrane covered by mitochondria (at levels of <10%, 10–50%, or >50%) was recorded. The large increase in subsarcolemmal mitochondria in the K19-null mouse and the smaller increase in the desmin-null mouse are absent in the DKO mouse.