Electron microscopic observations on lysosomes and related cytoplasmic components of normal and pathological cardiac muscle

An electron microscopic investigation was made on lysosomes and morphologically related structures found in cardiac muscle. The tissues used in this investigation were obtained from normal and functionally altered rat hearts and human hearts from patients with cardiomyopathy. Structures morphologically similar to lysosomes were encountered in all hearts, but were especially numerous in the damaged hearts, both human and rat. These structures were extremely variable in size, the smaller ones being located in the Golgi region where they appeared to originate. Lipofuscin granules were especially numerous in pathological hearts, and have several morphological features in common with lysosomes. Other bodies were also frequently encountered in these cells which in many ways resembled lysosomes, but contained mitochondria, fragments of mitochondria and myelin figures. The structural similarities between lysosomes and these other elements lead us to consider the possibility that the latter structures may be modified, degenerate, or simply functional stages of lysosomes.