Intracisternal crystalline arrays of coated parallel tubules in cells of a human osteosarcoma.

Crystalline arrays of coated parallel tubules (CPT) were observed by electron microscopy within dilated cisternae of the rough endoplasmic reticulum of pleomorphic mononuclear cells in a human osteosarcoma. The wall of the peculiar intracisternal tubules consisted of an electron-dense thin membrane-like envelope which appeared to be composed of granular subunits. The electron-lucent tubular core together with the limiting envelope was approximately 15 nm in diameter. A coat of fuzzy material, approximately 10 nm thick, tightly surrounded the membrane-like wall of the tubules. Cross sections of accumulations of CPT showed the tubules to be arranged in a hexagonal crystalline array. The nature and significance of the intracisternal CPT are unknown.