Wang E, Brown P S, Aroeti B, Chapin S J, Mostov K E, Dunn K W
Department of Medicine, Indiana University School of Medicine, 1120 South Drive, FH115, Indianapolis, IN 46202-5116, USA.
Traffic. 2000 Jun;1(6):480-93. doi: 10.1034/j.1600-0854.2000.010606.x.
Quantitative confocal microscopic analyses of living, polarized MDCK cells demonstrate different pH profiles for apical and basolateral endocytic pathways, despite a rapid and extensive intersection between the two. Three-dimensional characterizations of ligand trafficking demonstrate that the apical and basolateral endocytic pathways share early, acidic compartments distributed throughout the medial regions of the cell. Polar sorting for both pathways occurs in these common endosomes as IgA is sorted from transferrin to alkaline transcytotic vesicles. While transferrin is directly recycled from the common endosomes, IgA is transported to a downstream apical compartment that is nearly neutral in pH. By several criteria this compartment appears to be equivalent to the previously described apical recycling endosome. The functional significance of the abrupt increase in lumenal pH that accompanies IgA sorting is not clear, as disrupting endosome acidification has no effect on polar sorting. These studies provide the first detailed characterizations of endosome acidification in intact polarized cells and clarify the relationship between the apical and basolateral endocytic itineraries of polarized MDCK cells. The extensive mixing of apical and basolateral pathways underscores the importance of endocytic sorting in maintaining the polarity of the plasma membrane of MDCK cells.
对活的、极化的MDCK细胞进行的定量共聚焦显微镜分析表明，尽管顶端和基底外侧内吞途径之间存在快速而广泛的交叉，但它们具有不同的pH分布。配体运输的三维特征表明，顶端和基底外侧内吞途径共享分布在细胞内侧区域的早期酸性区室。两种途径的极性分选发生在这些共同的内体中，因为IgA从转铁蛋白中被分选到碱性转胞吞小泡中。当转铁蛋白直接从共同的内体中循环利用时，IgA被运输到一个下游的顶端区室，其pH值接近中性。根据几个标准，这个区室似乎等同于先前描述的顶端回收内体。伴随IgA分选的管腔内pH值突然升高的功能意义尚不清楚，因为破坏内体酸化对极性分选没有影响。这些研究首次详细描述了完整极化细胞内体酸化的特征，并阐明了极化MDCK细胞顶端和基底外侧内吞途径之间的关系。顶端和基底外侧途径的广泛混合强调了内吞分选在维持MDCK细胞质膜极性中的重要性。
