Mechanism of insulin uptake in rat alveolar type II and type I-like epithelial cells.
The mechanism underlying the handling of protein and peptide drugs such as insulin in alveolar epithelial cells is still unclear. We therefore examined fluorescein isothiocyanate-labeled (FITC)-insulin uptake in rat primary cultured alveolar type II epithelial cells and in transdifferentiated type I-like cells. FITC-insulin uptake in these cells was much higher than those of FITC-immunoglobulin (IgG), transferrin, and dextran. FITC-insulin uptake was time- and concentration-dependent, and was almost completely inhibited by metabolic inhibitors in both cells, while bafilomycin A(1) inhibited the uptake only in type II cells. Inhibitors of clathrin- and caveolae-mediated endocytosis did not affect FITC-insulin uptake in either type of cell. Dynasore, a dynamin GTPase inhibitor, potently inhibited FITC-insulin uptake in type II cells. These results suggest that the characteristics of insulin uptake in type II and type I cells are different, and dynamin-dependent endocytosis that utilizes neither clathrin nor caveolae is involved in type II cells, while a dynamin-independent pathway is mainly involved in type I cells.
Department of Pharmaceutics and Therapeutics, Graduate School of Biomedical Sciences, Hiroshima University, Japan..
Mika
M
Ikehata
Ryoko
R
Yumoto
Yuki
Y
Kato
Junya
J
Nagai
Mikihisa
M
Takano
D000818:Animals; D001692:Biological Transport; D021941:Caveolae / Q000378:metabolism; D002478:Cells, Cultured; D002966:Clathrin / Q000378:metabolism; D003911:Dextrans / Q000378:metabolism; D004705:Endocytosis; D004847:Epithelial Cells / Q000378:metabolism*; D016650:Fluorescein-5-isothiocyanate / Q000031:analogs & derivatives* / Q000493:pharmacokinetics; D006835:Hydrazones / Q000378:metabolism; D007074:Immunoglobulin G / Q000378:metabolism; D007328:Insulin / Q000031:analogs & derivatives* / Q000493:pharmacokinetics; D018942:Macrolides / Q000378:metabolism; D008297:Male; D011650:Pulmonary Alveoli / Q000166:cytology / Q000378:metabolism*; D051381:Rats; D017207:Rats, Sprague-Dawley; D020545:Respiratory Mucosa / Q000378:metabolism*; D014168:Transferrin / Q000378:metabolism
D002966:Clathrin; D003911:Dextrans; D006835:Hydrazones; D007074:Immunoglobulin G; D007328:Insulin; D018942:Macrolides; C511794:N'-(3,4-dihydroxybenzylidene)-3-hydroxy-2-naphthahydrazide; D014168:Transferrin; C031573:insulin, fluorescein-isothiocyanated-; C040929:bafilomycin A1; D016650:Fluorescein-5-isothiocyanate