COMPARATIVE MORPHOLOGICAL STUDY ON THE FINE STRUCTURE OF PERISINUSOIDAL WALL OF RAT LIVER REVEALED BY FREEZE-REPLICAS AND THIN SECTIONS WITH SPECIAL REFERENCE TO ITO'S FAT-STORING CELL

Abstract

Ito's fat-storing cells in the rat liver were examined both as freeze-replicas and thin sections under the lipid repleting condition of the cell induced by the administration of vitamin A. Increased lipid droplets were fractured either with a depression surface or a bulge, on which a few thin, fractured layer piles were observed. Some of them were consisted of a number of concentric, thin lamellae of the layer, which clearly revealed, their multilayered structure in replicas. Lipid droplets exhibiting a flat fractured surface with a coarse, rugged structure were also observed. Besides these structures, there appeared lipid droplets exhibiting heterogeneity : one with a lamellar structure only at the periphery, or others containing two or three irregularly shaped spherules in a droplet with a lamellar structure respectively. At the time of fusion of each lipid droplet in Ito's cell, some peripheral thin layers fused with each other and continuity of the attached droplets occurred, and in some cases a club-like protrusion from one side of the fused droplet to the other was observed. Many figures corresponding to those of freeze-replicas were ascertained also by means of the thin sections. The results of this study suggest that these lipid droplets with lamellar structure may contain phospholipids, and it is considered that the vitamin A (retinol) incorporated in these lamellar lipid droplets of Ito's cell may arrange and be stored themselves among the phospholipid molecules. Distribution frequency of pores on the nuclear envelope of Ito's cell is less than that of hepatocytes. Concerning the Kupffer cells, they have a tendency to make small sparsely distributed groups of nuclear pores and they are less numerous than the Ito's cell. On the surface of Ito's cell many pinocytotic invaginations were found and intramembranous particles were most frequent on the P face and tended to form distinct clusters in some cases.