Comparison of albumin uptake in rat alveolar type II and type I-like epithelial cells in primary culture.
OBJECTIVE
To elucidate and compare the activity and mechanism of albumin uptake in primary cultured alveolar type II and type I-like epithelial cells.


METHODS
Type II epithelial cells isolated from rat lungs were cultured for 2 days at 5 x 10(6) cells/35-mm dish or for 6 days at 2 x 10(6) cells/35-mm dish. The mRNA expression of marker genes and FITC-albumin uptake were examined.


RESULTS
The cells cultured for 2 days exhibited cuboidal type II epithelial morphology with lamellar bodies inside the cells, while the cells cultured for 6 days exhibited squamous type I epithelial morphology. These morphological characteristics were consistent with the changes in mRNA expression pattern of marker genes. FITC-albumin uptake in both cells was temperature-dependent and was inhibited by metabolic inhibitors and bafilomycin A1. The rate of uptake was much higher in type II cells than type I-like cells. In both cells, FITC-albumin uptake was inhibited by clathrin mediated-endocytosis inhibitors, but not by caveolae mediated-endocytosis inhibitors.


CONCLUSIONS
These findings indicate that albumin in alveolar lining fluid is internalized into type II and type I epithelial cells via clathrin-mediated endocytosis, and the rate of albumin uptake is higher in type II cells than type I cells.
Ikehata
Mika
M
Department of Pharmaceutics and Therapeutics, Graduate School of Biomedical Sciences, Hiroshima University, 1-2-3 Kasumi, Minami-ku, Hiroshima, 734-8553, Japan.
Yumoto
Ryoko
R
Nakamura
Kosuke
K
Nagai
Junya
J
Takano
Mikihisa
M
D000818:Animals; D021941:Caveolae / Q000378:metabolism; D048430:Cell Shape; D054338:Cell Transdifferentiation; D002478:Cells, Cultured; D002966:Clathrin / Q000378:metabolism; D004705:Endocytosis / Q000187:drug effects; D004791:Enzyme Inhibitors / Q000494:pharmacology; D004847:Epithelial Cells / Q000187:drug effects / Q000201:enzymology / Q000378:metabolism*; D016650:Fluorescein-5-isothiocyanate / Q000031:analogs & derivatives* / Q000378:metabolism; D005786:Gene Expression Regulation; D007700:Kinetics; D008297:Male; D011650:Pulmonary Alveoli / Q000166:cytology / Q000187:drug effects / Q000201:enzymology / Q000378:metabolism*; D012333:RNA, Messenger / Q000378:metabolism; D051381:Rats; D017207:Rats, Sprague-Dawley; D012709:Serum Albumin / Q000378:metabolism*; D013696:Temperature; D014475:Uncoupling Agents / Q000494:pharmacology
D002966:Clathrin; D004791:Enzyme Inhibitors; C518288:FITC-albumin; D012333:RNA, Messenger; D012709:Serum Albumin; D014475:Uncoupling Agents; D016650:Fluorescein-5-isothiocyanate