Mitotic Structures of Aortic Smooth Muscle Cells in Swine and in Culture: Paired Cistemae

Seventeen, nine and six mitotic cells were ultrastructurally observed in 6 months old and fetal swine aortas and in cultured aortic medial cells. They had ultrastructurai features of the smooth muscle cell such as myofllaments, fusiform densities, pinocytotic vesicles and basement membranes. The mitotic cells in the wall of the aortas were located mainly in the inner and middle layers of the media and were characterized by a low electron dense cytoplasm, sparse and mainly peripheral myofilaments and fusiform densities, and paired cistemae. Paired cistemae were Irregularly shaped, branched and approximately 6 ftm in length. The confronted two membranes were smooth surfaced and close together; they were separated by a regular 30 nm gap containing an electron-opaque material. The width of the cistemae was irregular, varying from 20 nm to 40 nm. The portions of outer membranes were occasionally dotted with ribosomes. Paired cistemae were present not only in the central areas but also in the peripheral areas of the cytoplasm during prophase. They were not present in any smooth muscle cells durin