Electron microscopic study on the sinusoidal wall of the liver in the flatfish, Kareius bicoloratus: demonstration of numerous desmosomes along the sinusoidal wall.

The liver of the flatfish, Kareius bicoloratus was observed by transmission electron microscopy. The hepatocytes surround the bile canaliculi and are loosely disposed with few connections in between. The architecture of the hepatic tissue is first supported by junctional complexes between hepatocytes abutting on the bile canalicular lumen, second, by intraparenchymal bile ductules connecting with hepatocytes through desmosomes and third, by particular "desmosomal complexes" composed of numerous desmosomes arranged along the interhepatocytic space and accompanied by bundles of microfilaments in the cells. The fourth, and most important supporting factor of the hepatic tissue, consists of sinusoidal cells including adjacent hepatocytes connected by many desmosomes. The Disse's space lacks collagen fibrils but contains filaments of type IV collagen. Sinusoidal cells are reinforced by abundant microfilaments in their cytoplasm. Desmosomes occur between endothelial cells, which are further connected by other desmosomes to hepatocytes as well as Ito cells. Desmosomes are most numerous around the Ito cells. Thus, the cells forming the sinusoidal wall are interconnected by many desmosomes, forming as a whole a strong framework which supports the hepatic tissue. The desmosomes between the sinusoidal cells are characterized, except for those between endothelial cells themselves, by the presence of zones of microfilaments on both of their sides which extend parallel to the desmosomal plaques and are believed to strengthen the desmosomal connection. No Kupffer cells could be identified in the sinusoid, but macrophages were demonstrated in the parenchyma near the Disse's space.