Disorganization and reestablishment of cardiac muscle cell ultrastructure in cultured adult rat ventricular muscle cells

Abstract

Adult rat ventricular cardiac muscle cells were isolated enzymatically and cultured for 1 to 9 days. At various times after being placed in culture, the cells were fixed and processed by standard methods for transmission electron microscopic (TEM) examination. Cardiac muscle cells were well organized immediately after isolation. Most cells, however, became disorganized with respect to sarcomeric arrangement after 24 hr in culture. Moreover, most of the cells showed evidence of dissociation-related damage, such as large surface blebs and bloated mitochondria. Although sarcomere organization was profoundly disturbed, some minimal signs of prior filament interrelations persisted. By 3 days in culture, the cells were still disorganized. They were, however, attached to the surface of the culture flask. From 5 to 9 days in culture, the myocytes reconstructed typical cardiac muscle ultrastructural features. Ultrastructural evidence for protein synthesis was abundant, and the cells appeared to reorganize their contractile apparatus using a mechanism similar to that which occurs during normal mammalian cardiac muscle cell differentiation. Other myocyte features which reappeared as the myofilaments reorganized included intercalated discs, sarcoplasmic reticulum (SR), and the transverse tubular (T) system. Some patent elements of the T system persisted throughout the process of reorganization. Our studies also indicated that most of the lipofusein granules present in the cultured cells were of de novo origin.