Fine structure of the sinusoidal wall in the liver of fresh-water catfish (Parasilurus asotus), with special reference to the smooth muscle cells.

The ultrastructure of the hepatic perisinusoidal spaces of the fresh-water catfish was examined by electron microscopy. The hepatic sinusoidal wall of the catfish consists of endothelial cells, Ito's fat-storing cells and smooth muscle cells, but is devoid of Kupffer cells. The present study demonstrates the sporadic occurrence of smooth muscle cells in the perisinusoidal spaces of catfish liver. This seems to be the first report on smooth muscle cells in the perisinusoidal spaces of vertebrate livers. The location of these muscle cells indicates that they may be responsible for the regulation of the sinusoidal blood flow by their contraction, thus functioning as a sphincter.