Ultrastructure of cardiocyte degeneration and myocardial calcification in the dystrophic hamster.

The myocardium of the Bio 14.6 cardiomyopathic hamster was examined with the electron microscope to identify cellular and organelle changes during the acute lesioning stage, a period typified by concomitant cardiocyte destruction and calcium elevation. Most cardiocytes retained their normal histologic and ultrastructural features, but scattered foci of altered and necrotic cells were observed in association with degenerative calcifying lesions. Prenecrotic alterations of myocytes included cellular edema; varying degrees of distension of sarcoplasmic reticulum and T-tubules; contraction bands and other myofibrillar abnormalities; mitochondrial clustering and hyperplasia; a wide spectrum of mitochondrial changes such as altered sizes, shapes, and cristal patterns, and increases in the number and size of osmiophilic matrix inclusions. Morphologic features consistent with substantial calcium excess were not observed in most altered but prenecrotic cells. Instead, calcium deposition within extruded mitochondria and upon degenerating organelle debris was observed only after cardiocyte disruption. Some calcifying cell remnants were phagocytized by macrophages, whereas large calcified plaques and other deposits remained in the interstitium. Mitochondrial calcification in vascular smooth muscle cells and fibroblasts was evident in highly calcified lesions. These observations suggest that most of the morphologically identifiable calcium deposition present in this cardiomyopathy results from secondary calcification subsequent to sarcolemmal disruption.