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Molecular Biology of the Cell Vol. 11, 21312150, June 2000

Summary: Molecular Biology of the Cell
Vol. 11, 21312150, June 2000
Sorting of Membrane and Fluid at the Apical Pole of
Polarized Madin-Darby Canine Kidney Cells
Som-Ming Leung, Wily G. Ruiz, and Gerard Apodaca*
Renal-Electrolyte Division of the Department of Medicine, Laboratory of Epithelial Biology, and
Department of Cell Biology and Physiology, University of Pittsburgh, Pittsburgh, Pennsylvania 15261
Submitted December 8, 1999; Revised February 18, 2000; Accepted March 21, 2000
Monitoring Editor: Suzanne R. Pfeffer
When fluid-phase markers are internalized from opposite poles of polarized Madin-Darby canine
kidney cells, they accumulate in distinct apical and basolateral early endosomes before meeting in
late endosomes. Recent evidence suggests that significant mixing of apically and basolaterally
internalized membrane proteins occurs in specialized apical endosomal compartments, including
the common recycling endosome and the apical recycling endosome (ARE). The relationship
between these latter compartments and the fluid-labeled apical early endosome is unknown at
present. We report that when the apical recycling marker, membrane-bound immunoglobulin A
(a ligand for the polymeric immunoglobulin receptor), and fluid-phase dextran are cointernalized
from the apical poles of Madin-Darby canine kidney cells, they enter a shared apical early
endosome ( 2.5 min at 37C) and are then rapidly segregated from one another. The dextran
remains in the large supranuclear EEA1-positive early endosomes while recycling polymeric


Source: Apodaca, Gerard - Departments of Medicine & Cell Biology and Physiology, University of Pittsburgh


Collections: Biology and Medicine