title: Tubular invaginations with caveolae and coated pits in the sinus endothelial cells of the rat spleen.
abstract: The fine structure of plasmalemmal tubular invaginations with caveolae and coated pits in the sinus endothelial cells of the rat spleen has been demonstrated by scanning and transmission electron microscopy. In addition, the three-dimensional structure of the tubular invagination has been revealed by computer-aided reconstruction. The tubular invaginations of the plasma membrane plunged into the cytoplasm everywhere from the apical, lateral, and basal surfaces of the plasma membrane. The invaginations were tubular and branched away, and their plasma membranes were reinvaginated to form numerous caveolae and occasional coated pits. Numerous caveolae were found in clusters that looked similar to a bunch of grapes and the coated pits were present at the base of the clusters. The caveolae and coated pits derived from the tubular invaginations were almost ultrastructurally identical to those derived from the surface plasma membrane. From examination of the fractured surfaces of the endothelial cells treated with the aldehyde prefix osmium-dimethyl sulfoxide-osmium method and of ultrathin sections of those infiltrated by lanthanum nitrate, the tubular invaginations were found to not penetrate any endothelial cells. A computer-aided reconstruction revealed that the caveolae derived from the tubular invaginations were in close apposition to the surface-connected canaliculi. The reaction product of Concanavalin A conjugated to horseradish peroxidase was present on the outer leaflet of the membranes of the coated pits and coated vesicles and also in the contents of the endosomes, but it was absent from any caveolae. Based on our observations, the functional significance of the tubular invaginations in sinus endothelial cells is discussed.
authors.affiliation: Department of Anatomy, School of Medicine, Fukuoka University, 7-45-1, Nanakuma, Jonan-ku, Fukuoka, 814-0180 Japan. kiyokoue@fukuoka-u.ac.jp
authors.forename: K
authors.initials: K
authors.lastname: Uehara
authors.forename: M
authors.initials: M
authors.lastname: Miyoshi
mesh_terms: D000818:Animals; D002462:Cell Membrane / Q000648:ultrastructure; D003208:Concanavalin A; D004730:Endothelium, Vascular / Q000166:cytology / Q000648:ultrastructure; D006651:Histocytochemistry; D006735:Horseradish Peroxidase; D007091:Image Processing, Computer-Assisted; D007811:Lanthanum; D037102:Lectins; D008297:Male; D008854:Microscopy, Electron; D008855:Microscopy, Electron, Scanning; D008870:Microtubules / Q000648:ultrastructure*; D051381:Rats; D017208:Rats, Wistar; D013154:Spleen / Q000166:cytology / Q000648:ultrastructure*
chemical_list: D037102:Lectins; D003208:Concanavalin A; C016534:lanthanide nitrate; D007811:Lanthanum; D006735:Horseradish Peroxidase