title: Transferrin receptor polarity and recycling accuracy in "tight" and "leaky" strains of Madin-Darby canine kidney cells.
abstract: We have characterized the polarity of the transferrin receptor in the epithelial Madin-Darby canine kidney (MDCK) cell line. The receptor is present in approximately 165,000 copies per cell, migrates as a diffuse band upon SDS gel electrophoresis with Mr 90,000, displays a dissociation constant for diferritransferrin at neutral pH of approximately 2 nM, and is active in essentially all of the cells of the population. Transferrin-mediated 55Fe uptake was used to measure the polarity of active transferrin receptors in filter-grown MDCK cells. The ratio of basolateral to apical receptors was approximately 800:1 for the high resistance strain I MDCK cells (typically greater than 2,000 ohm X cm2) and approximately 300:1 for the lower resistance strain II cells (less than 350 ohm X cm2). In combination with morphometric data this shows that a difference in resistance between these two strains is not reflected in a significant difference in cell surface polarity. We used the recycling of transferrin receptor in filter-grown MDCK cells to evaluate the accuracy of the sorting of a basolateral protein during endocytosis. Monitoring the amount of apically released 125I-labeled transferrin after application of 55Fe- and 125I-labeled transferrin to the basolateral surface provided a sensitive assay of the accuracy of sorting during recycling of the receptor from endosomes to the plasma membrane. The accuracy of transferrin receptor sorting (greater than 99.88%) during a single cycle of transit between the endosome and the plasma membrane is sufficient to maintain the high level of polarity of the cell.
mesh_terms: D000818:Animals; D001692:Biological Transport; D002451:Cell Compartmentation; D002460:Cell Line; D004285:Dogs; D004705:Endocytosis; D011992:Endosomes / Q000378:metabolism; D004848:Epithelium / Q000378:metabolism* / Q000648:ultrastructure; D005089:Exocytosis; D005374:Filtration / Q000295:instrumentation; D006863:Hydrogen-Ion Concentration; D007158:Immunologic Techniques; D007365:Intercellular Junctions / Q000502:physiology; D007501:Iron / Q000378:metabolism; D010969:Plastics; D011990:Receptors, Transferrin / Q000378:metabolism*; D014168:Transferrin / Q000378:metabolism*
chemical_list: D010969:Plastics; D011990:Receptors, Transferrin; D014168:Transferrin; D007501:Iron