Electron microscopic study on the hepatic sinusoidal wall of the soft-shelled turtle (Amyda japonica) with special remarks on the smooth muscle cells.

The hepatic sinusoids of the soft-shelled turtle (Amyda japonica) were examined by transmission electron microscopy. The sinusoidal wall was composed of endothelial cells, Kupffer cells and Ito cells. The basal surface of the hepatocyte facing the Disse's space was covered by a continuous basal lamina. In addition to the Ito cells, the Disse's space contains a considerable number of smooth muscle cells. Many of these were distributed sporadically, while others appeared as a sphincter circling the sinusoid. The smooth muscle cells in the Disse's space showed the following features: 1) The nucleus was located eccentrically near one end of the cell. 2) The surface vesicles and pits, mitochondria and dense patches along the myofilament bundles were all sparse as compared with those known from mammalian smooth muscle cells. 3) Cytoplasmic processes or ruffles were protruded into the Disse's space. 4) A weak basal lamina could be recognized. Sinusoidal endothelial cells were characterized by many large electron lucent lysosomes in their perikaryon and by small fenestrae in their attenuated cytoplasm. Ito cells sending out several cytoplasmic processes, possessed a single large lipid droplet on one side of the nucleus. A single cilium budding from the distal centriole into the Disse's space was found in an Ito cell. Extrasinusoidal macrophages were considerably numerous in the soft-shelled turtle liver. Some of the macrophages were apparently migrating into the sinusoid, there to presumably transform into the Kupffer cells.