Electron Microscope Study on the Hepatic Sinusoidal Wall and Fat-Storing Cells in the Bat

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Abstract
The 3 cell types known to form the hepatic sinuosoidal wall were observed by EM in 3 kinds of bats [Myotis macrodactylus Rhinolophus cornutus Miniopterus schreibersi] captured in winter and summer. The cytoplasmic extensions of sinusoidal endothelial cells consisted of continuous thicker parts (cytoplasmic processes) and discontinuous thinner parts (sieve plates). The alternate disposition of the 2 parts was rather irregular and the sizes, shapes and spacings of the fenestrae were variable. In the thinner parts with numerous small fenestrae, larger gaps were also mingled. The endothelium was simple-layered and devoid of basal lamina. Interendothelial junctions were found mainly between closely apposed margins of the cytoplasmic processes and agreed in structure with the Wisse junctional complex. Kupffer cells, morphologically distinct from the endothelial cells, bulged strongly into the sinusoidal lumen. Provided with many microvillous pseudopods, they were stellate in appearance. They were fixed to the endothelial lining by small junctional areas which occurred between the Kupffer cell body and the cytoplasmic processes of the endothelium. Fat-storing cells were located in the Disse space. They generally contained only smaller amounts of lipid in a few droplets. So-called empty fat-storing cells were numerous, especially in winter bats. The perikaryonal cytoplasm revealed a large Golgi complex and well-developed granular endoplasmic reticulum. The 3 mesenchymal cell types of the sinusoidal wall possessed the centriole in common within the Golgi complex, but only the fat-storing cell was provided with the single celium. Fat-storing cells extended cytoplasmic processes ramifying beneath the endothelial lining occasionally surrounding the sinusoids almost completely, which seemed to reinforce the endothelial lining and bring about constriction of the sinusoid. In hypervitaminotic bats, receiving 6,000 IU vitamin A for 3 days, a remarkable increase in size and number of lipid droplets was observed in slight hypertrophic fat-storing cells and the empty cells disappeared simulating an increased number of fat-storing cells. Suggestion was made of an antidotal function of fat-storing cells against excess vitamin A which might be considered a toxic agent in the broad sense. The Disse space of bat liver contained plasma cells, lymphocytes and macrophages, the latter 2 often being under migration through the endothelial fenestrae.