The livers of rats were fixed by perfusion with glutaraldehyde, treated with the revised tannin-osmium method of MURAKAMI (1974), freeze-cracked by the method of TOKUNAGA et al. (1974), critical point dried and vacuum-evaporated with a thin metal layer. The endothelial cells and Kupffer cells of liver sinusoids were examined under the scanning electron microscope (SEM).
The endothelial cells lining the sinusoids showed numerous intracellular openings which were partly large fenestrations (1-3μm) and partly small pores (less than 0.1μm). Endothelial cells with a wavy outline are partly overlapped loosely and partly closely attached. Stomata of various sizes were also found between the cells, which were rather scarce as compared with the intracellular fenestrations. At the junctional parts of a sinusoid with both a central vein and a portal canal, only the small pores were found. The sinusoids in these areas thus had the nature of the ordinary“pored capillary.”The large fenestrations occurred in the main, intermediate portion of the sinusoid and the space of Disse was widely continuous through them to the sinusoidal lumen.
Kupffer cells were numerous in the periportal area and showed surface morphology distinctly different from the thin fenestrated endothelial cells. Numerous cytoplasmic processes were projected from the surface of this cell, which were classified into three types: 1) thick, horizontal cytoplasmic processes, 2) microvillous processes and 3) filo- and lamellipodia. Microvillous processes densely covered the surface of the cell. Filopodia radiated from the margin of the cell and attached to the surface of the adjacent endothelial cells. Lamellipodia were observed spreading widely on the surface of the sinusoidal wall. The Kupffer cell generally lies on a large endothelial opening and is anchored to its margin by the filopodia. The present study also demonstrated a filopodial communication between adjacent Kupffer cells. The morphological similarity of the Kupffer cell with the macrophage cultured in vitro was stressed in this study.