Role of clathrin- and actin-dependent endocytotic pathways in lung phospholipid uptake.
We evaluated the contribution of endocytotic pathways to pulmonary uptake of surfactant lipids from the alveolar space. Resting and stimulated 8-bromoadenosine 3',5'-cyclic monophosphate (8-Br-cAMP) uptake of unilamellar liposomes labeled with either [(3)H]dipalmitoylphosphatidylcholine ([(3)H]DPPC) or 1-palmitoyl-2-[12-(7-nitro-2-1,3-benzoxadiazol-4-yl) amino] dodecanoyl-phosphatidylcholine (NBD-PC) was studied in isolated perfused rat lungs and isolated type II cells. Amantadine and phenylarsine oxide, inhibitors of clathrin-mediated endocytosis, each decreased [(3)H]DPPC uptake under resting conditions by approximately 40%; their combination had no additional effect. Cytochalasin D, an inhibitor of actin-dependent processes, reduced liposome uptake by 55% and potentiated the effect of either clathrin inhibitor alone. Relative inhibition for all agents was higher in the presence of 8-Br-cAMP. The effect of inhibitors was similar for liposomes labeled with [(3)H]DPPC or NBD-PC. By fluorescence microscopy, NBD-PC taken up by lungs was localized primarily to alveolar type II cells and was localized to lamellar bodies in both lungs and isolated cells. These studies indicate that both clathrin-mediated and actin-mediated pathways are responsible for endocytosis of DPPC-labeled liposomes by alveolar type II cells in the intact lung.
Rückert
Peter
P
Institute for Environmental Medicine, University of Pennsylvania School of Medicine, Philadelphia, Pennsylvania 19104, USA.
Bates
Sandra R
SR
Fisher
Aron B
AB
D015060:1,2-Dipalmitoylphosphatidylcholine / Q000493:pharmacokinetics*; D009327:4-Chloro-7-nitrobenzofurazan / Q000031:analogs & derivatives* / Q000493:pharmacokinetics; D000199:Actins / Q000378:metabolism*; D000818:Animals; D002478:Cells, Cultured; D002966:Clathrin / Q000378:metabolism*; D004705:Endocytosis / Q000502:physiology*; D008081:Liposomes / Q000378:metabolism; D008297:Male; D010477:Perfusion; D010713:Phosphatidylcholines / Q000493:pharmacokinetics; D011650:Pulmonary Alveoli / Q000166:cytology / Q000378:metabolism*; D051381:Rats; D017207:Rats, Sprague-Dawley; D014316:Tritium
D000199:Actins; D002966:Clathrin; D008081:Liposomes; D010713:Phosphatidylcholines; D014316:Tritium; C053903:1-palmitoyl-2-(12-((7-nitro-2,1,3-benzoxadiazol-4-yl)amino)dodecanoyl)phosphatidylcholine; D015060:1,2-Dipalmitoylphosphatidylcholine; D009327:4-Chloro-7-nitrobenzofurazan