Lamellar bodies of rat alveolar type 2 cells have late endosomal marker proteins on their limiting membranes.
Alveolar type 2 cells are known to take up surfactant phospholipids and proteins from the alveolar space and recycle them into secretory organelles via a receptor-mediated endocytic pathway. To clarify the intracellular route(s) through which materials ingested by the cells are processed, we examined the immunocytochemical localization of late endosomal and lysosomal membrane markers, rab 7 and lamp 1 proteins, within rat alveolar type 2 cells. The limiting membranes of lamellar bodies (LBs) showed positive immunoreactivity for both proteins, whereas multivesicular bodies (MVBs) exhibited positive immunoreactivity only for lamp 1 protein on free vesicles in the MVB lumen. From these findings, it is suggested that LBs are not only secretory granules, but also constitute one of the late endosomal compartments of the cells and that MVBs of this cell type may be targeted to cell organelle(s) other than lysosomes.
Wasano
K
K
Department of Anatomy, Faculty of Medicine, Kyushu University, Fukuoka, Japan.
Hirakawa
Y
Y
D000595:Amino Acid Sequence; D000818:Animals; D015703:Antigens, CD; D015415:Biomarkers / Q000032:analysis; D003594:Cytoplasmic Granules / Q000378:metabolism; D011992:Endosomes / Q000737:chemistry* / Q000378:metabolism; D019204:GTP-Binding Proteins / Q000032:analysis*; D007425:Intracellular Membranes / Q000737:chemistry*; D051907:Lysosomal Membrane Proteins; D008247:Lysosomes / Q000737:chemistry / Q000378:metabolism; D008562:Membrane Glycoproteins / Q000032:analysis*; D008856:Microscopy, Fluorescence; D008969:Molecular Sequence Data; D011650:Pulmonary Alveoli / Q000737:chemistry* / Q000378:metabolism / Q000648:ultrastructure*; D011663:Pulmonary Surfactants / Q000378:metabolism; D011817:Rabbits; D051381:Rats; D017208:Rats, Wistar; D013347:Subcellular Fractions / Q000737:chemistry; D020691:rab GTP-Binding Proteins; D000090802:rab7 GTP-Binding Proteins
D015703:Antigens, CD; D015415:Biomarkers; D051907:Lysosomal Membrane Proteins; D008562:Membrane Glycoproteins; D011663:Pulmonary Surfactants; D000090802:rab7 GTP-Binding Proteins; D019204:GTP-Binding Proteins; D020691:rab GTP-Binding Proteins