Nickel sub-sulphide-induced leiomyosarcoma in rabbit white skeletal muscle: a light microscopical and ultrastructural study.

Nickel sub-sulphide-induced leiomyosarcomas in rabbit white skeletal muscle were studied by both light and electron microscopy. Two types of tumor cells, small spindle cells and elongated smooth muscle cells, are revealed by light microscopy. Nevertheless, their ultrastructure displays the same general feature. The most differentiated cells have abundant cytoplasmic filaments 7 nm in diameter, kept together in bundles by dense bodies. There also exist many 10 nm filaments and a large number of microtubules. The nuclei have prominent nucleoli with an extensive nucleolonema which form an irregular tridimensional network. Distinct fibrillar nuclear bodies were observed. Sometimes there exist desmosomes or gap junctions. The Golgi apparatus produces coated vesicles with secretory function. In the tumors were generally found the Ni3S2 implantations surrounded by a capsule, the major component of which were collagen fibers, degenerated nuclei and rod-like structures with a transverse periodicity of 15.5 nm. From these observations, several characteristics should be pointed out: 1) Many tumor cells contain large nucleoli and distinct intranuclear inclusions of undetermined nature. 2) The coated vesicles represent a secretory activity of the tumor cells; the coat material is probably used during the formation of cell membranes. Another possible function of coated vesicles could be the sequestering of calcium ions. 3) The rod-like structures in the Ni3S2-including capsule are not of Z-line material. 4) The tumoral stem myoblast in heart and skeletal muscle arise from mesenchymal cells.