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Am J Physiol ; 272(6 Pt 1): C1781-9, 1997 Jun.
Article in English | MEDLINE | ID: mdl-9227405

ABSTRACT

Na(+)-K(+)-ATPase is localized to the basolateral cell surface of most epithelial cells. Conflicting results regarding the intracellular trafficking of Na(+)-K(+)-ATPase in Madin-Darby canine kidney cells have been reported, with delivery to both apical and basolateral membranes or exclusively to the basolateral cell surface. We examined the delivery and steady-state distribution of Na(+)-K(+)-ATPase in the amphibian epithelial cell line A6 using an antibody raised against Na(+)-K(+)-ATPase alpha-subunit and sulfo-N-hydroxysuccinimidobiotin to tag cell surface proteins. The steady-state distribution of the Na(+)-K(+)-ATPase was basolateral, as confirmed by immunocytochemistry. Delivery of newly synthesized Na(+)-K(+)-ATPase to the cell surface was examined using [35S]methionine and [35S]cysteine in a pulse-chase protocol. After a 20-min pulse, the alpha-subunit and core glycosylated beta-subunit were present at both apical and basolateral cell surfaces. The alpha-subunit and core glycosylated beta-subunit delivered to the apical cell surface were degraded within 2 h. Mature alpha/beta-heterodimer was found almost exclusively at the basolateral surface after a 1- to 24-h chase. These data suggest that immature Na(+)-K(+)-ATPase alpha-subunit and core glycosylated beta-subunits are not retained in the endoplasmic reticulum of A6 cells and apparently lack sorting signals. Mature Na(+)-K(+)-ATPase is targeted to the basolateral surface, suggesting that basolateral targeting of the protein is conformation dependent.


Subject(s)
Cell Membrane/enzymology , Protein Processing, Post-Translational , Sodium-Potassium-Exchanging ATPase/metabolism , Animals , Cell Line , Cell Membrane/ultrastructure , Dogs , Epithelial Cells , Epithelium/enzymology , Kidney/enzymology , Models, Biological , Sodium-Potassium-Exchanging ATPase/biosynthesis , Sodium-Potassium-Exchanging ATPase/isolation & purification , Xenopus laevis
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