Blomhoff R, Nenseter M S, Green M H, Berg T
Institute for Nutrition Research, School of Medicine, University of Oslo, Norway.
Biochem J. 1989 Sep 1;262(2):605-10. doi: 10.1042/bj2620605.
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.
利用¹²⁵I-聚（乙烯基吡咯烷酮）（PVP）作为标记物，在分离的兔肝实质细胞中研究了液相内吞作用。首先，测定细胞对¹²⁵I-PVP的摄取。此外，细胞用¹²⁵I-PVP加载20、60和120分钟，并在120 - 220分钟内监测标记物的释放。然后我们使用模拟、分析和建模（SAAM）计算机程序以及基于模型的房室分析技术，为这些细胞中的液相内吞作用建立一个机制模型。为了同时拟合所有数据，需要一个具有三个细胞房室和一个细胞外房室的模型。这三个动力学上不同的细胞房室被解释为代表（1）早期内体，（2）一个相当于受体与配体解偶联区室（CURL）和/或多囊泡体（MVB）的前溶酶体区室，以及（3）溶酶体。该模型预测，内化的¹²⁵I-PVP中约80%从早期内体区室再循环到培养基中。这种再循环的表观一级速率常数为0.094分钟⁻¹，因此表明平均一个¹²⁵I-PVP分子在11分钟内被再循环。该模型还预测，向培养基的再循环发生在所有三个细胞内区室。从前溶酶体区室，预计40%的¹²⁵I-PVP分子再循环到培养基中，60%转移到溶酶体区室。从前溶酶体区室再循环到培养基的平均时间估计为66分钟。对于溶酶体区室中的¹²⁵I-PVP，每分钟有0.3%转移回培养基中。这些结果以及为解释数据而建立的模型预测，在兔肝实质细胞中，通过液相内吞作用内吞的物质会大量再循环到细胞外环境中。
