The Hepatic Sinusoidal Endothelial Cell 



153 



suggesting the appearance of intimate interdigita- 

 tion of two neighbouring cells. It is not known 

 whether, or to what extent, this relationship exists, 

 because it was occasionally possible to follow a cell 

 membrane far enough to get the impression that the 

 whole formation represented a complicated infolding 

 of the membrane of a single cell. 



One other type of intercellular relationship has 

 been described above; that of a trabecula from one 

 cell fitting into a tunnel in another cell. 



Relation of endothelial cell to subjacent structures. 

 — The surface of the hepatic cell was characterized 

 by a large number of simple and branched villous 

 extensions (2) of variable length (usually about 

 0.15-0.5 //) and about 0.025 /( in diameter. In 

 some sections a number of villi were cut longi- 

 tudinally and seen to extend all the way from 

 the main body of the hepatic cell below to the 

 endothelial cell above, while the spaces between 

 villi contained numerous transversely-sectioned cyto- 

 plasmic processes (fig. 1). Most of these latter proc- 

 esses were considered to be hepatic-cell villi or 

 their branches. Endothelial cells rested directly on 

 this bed of villi: no basement membrane was seen 

 between endothelial cell and hepatic cell. 



The mechanical attachment of endothelial cell to 

 hepatic cell appears to be effected, at least in part, 

 by an intermingling of villus-like processes of one 

 cell with similar processes from the other. This 

 relationship appeared not to be important in sec- 

 tions through cytoplasmic extensions some distance 

 from the endothelial cell nucleus; in fact only a few 

 cytoplasmic villi other than those of hepatic cells 

 were seen. However, in the vicinity of the endothelial 

 cell nucleus, branched villi projecting into the perisi- 

 nusoidal space from the endothelial cell often ap- 

 peared to be very numerous. Von Kupffer (6) described 

 and illustrated endothelial cell processes passing 

 between two hepatic cells toward the bile canal; a 

 single similar observation has been made in this 

 study, and it appears that this may be an important 

 anchoring mechanism. A special relationship be- 

 tween the reticular (collagenous) fibers in the perisi- 

 nusoidal space and endothelial cells has not yet been 

 observed. 



An incidental observation on the surface of the 

 hepatic cell next to the perisinusoldal space seems 

 worthy of mention here. Small membrane-enclosed 

 vaculoes have been seen in hepatic cells containing 

 one or more rounded bodies about 350 A in diameter 

 and somewhat denser than the ground cytoplasm. In 

 some instances these vacuoles were seen opening 

 into the perisinusoldal space and apparently dis- 

 charging their content of rounded bodies. 



Cell membranes. — The plasma membranes of both 

 the endothelial cell and hepatic cell villus have been 

 seen to be double in places, and apparently single 

 in others. The double-membraned condition is not 

 restricted to the luminal surface of the endothelial 

 cell; it has been seen on the basal side also. 



This study has shown that hepatic sinusoidal 

 endothelial cells of the mouse are most unusual in 

 shape. Nothing has been seen that is inconsistent 

 with the bi/arre pictures published by v. Kupffer (6). 

 The facts that there is extensive overlapping of cyto- 

 plasmic processes and in some cases trabecular proc- 

 esses of one cell pass through tunnels in other cells 

 tend to reconcile the idea of continuity of endothelial 

 lining with the irregularities of cell shape. 



In the absence of a basement membrane and inter- 

 cellular cement, endothelial cells appear to be 

 anchored in place by complicated relationships of 

 their cytoplasmic processes with other endothelial 

 cells and with subjacent hepatic cells. 



The following considerations argue that the perisi- 

 nusoldal space is an anatomical entity of physio- 

 logical significance: There is no basement membrane 

 between endothelial lining and hepatic cell. There is 

 no intercellular cement, as manifested by the fact 

 that colloidal particles (and therefore presumably 

 blood plasma) pass from the blood stream between 

 endothelial cells into the space. The hepatic cell 

 surface area is enlarged by villi even in places where 

 the under surfaces of endothelial cytoplasmic sheets 

 appear completely flat (the hepatic cell surface is 

 thus apparently designed to carry on exchange of 

 materials at a much greater rate than that of the cell 

 interposed between it and the blood stream). Small 

 rounded bodies are secreted by the hepatic cell into 

 the fiuid filling the perisinusoldal space. 



If, as it appears from the above, blood plasma 

 actually comes into direct contact with the hepatic 

 cell, then the question of continuity or discontinuity 

 of endothelial lining decreases in importance. 



It is a pleasure to express thanks to Dr. F. S. Sjostrand 

 for the use of his laboratory facilities. 



References 



1. Eppinger, H., Die Permeabilitats-Pathoiogie als die Lehre 



vom Krankheitsbeginn, p. 569. Wicn, 1949. 



2. Fawcktt, D., J. Natl. Cancer Inst. 15 (Supplement), 



1475-1502(1955). 



3. Fellinger, K., Braunsteiner, H., and Pakesch, F., 



Mien. Klin. Hochschr. 65, 738-740 (1953). 



4. Hoffman, F. and von Recklinghausen, F., Zenir. meet. 



IViss. 5, 481-482 (1867). 



5. Parks, H. and Ciiiquoine, A. These Proceedings, p. 155. 



6. VON Kupffer, C, Arcli. niikroskop. Aiuii. ii. luUHick- 



liingsmech. 54, 254-284 (1899). 



