Fluid-phase endocytosis was studied in isolated rabbit liver parenchymal cells by using 125I-poly(vinylpyrrolidone) (PVP) as a marker. First, uptake of 125I-PVP by cells was determined. Also, cells were loaded with 125I-PVP for 20, 60 and 120 min, and release of marker was monitored for 120-220 min. Then we used the Simulation, Analysis and Modeling (SAAM) computer program and the technique of model-based compartmental analysis to develop a mechanistic model for fluid-phase endocytosis in these cells. To fit all data simultaneously, a model with three cellular compartments and one extracellular compartment was required. The three kinetically distinct cellular compartments are interpreted to represent (1) early endosomes, (2) a prelysosomal compartment equivalent to the compartment for uncoupling of receptor and ligand (CURL) and/or multivesicular bodies (MVB), and (3) lysosomes. The model predicts that approx. 80% of the internalized 125I-PVP was recycled to the medium from the early-endosome compartment. The apparent first-order rate constant for this recycling was 0.094 min-1, thus indicating that an average 125I-PVP molecule is recycled in 11 min. The model also predicts that recycling to the medium occurs from all three intracellular compartments. From the prelysosomal compartment, 40% of the 125I-PVP molecules are predicted to recycle to the medium and 60% are transferred to the lysosomal compartment. The average time for recycling from the prelysosomal compartment to the medium was estimated to be 66 min. For 125I-PVP in the lysosomal compartment, 0.3%/min was transferred back to the medium. These results, and the model developed to interpret the data, predict that there is extensive recycling of material endocytosed by fluid-phase endocytosis to the extracellular environment in rabbit liver parenchymal cells.
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September 1989
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Research Article|
September 01 1989
A multicompartmental model of fluid-phase endocytosis in rabbit liver parenchymal cells
R Blomhoff;
R Blomhoff
*Institute for Nutrition Research, School of Medicine, University of Oslo, P.O. Box 1046, 0316 Oslo 3, Norway.
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M S Nenseter;
M S Nenseter
*Institute for Nutrition Research, School of Medicine, University of Oslo, P.O. Box 1046, 0316 Oslo 3, Norway.
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M H Green;
M H Green
†Nutrition Department, Pennsylvania State University, University Park, PA 16802, U.S.A.
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T Berg
T Berg
*Institute for Nutrition Research, School of Medicine, University of Oslo, P.O. Box 1046, 0316 Oslo 3, Norway.
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Publisher: Portland Press Ltd
Online ISSN: 1470-8728
Print ISSN: 0264-6021
© 1989 London: The Biochemical Society
1989
Biochem J (1989) 262 (2): 605–610.
Citation
R Blomhoff, M S Nenseter, M H Green, T Berg; A multicompartmental model of fluid-phase endocytosis in rabbit liver parenchymal cells. Biochem J 1 September 1989; 262 (2): 605–610. doi: https://doi.org/10.1042/bj2620605
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