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A more recent version of this article appeared on March 1, 2005
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Submitted on March 29, 2004
Revised on November 5, 2004
Accepted on December 6, 2004
-Subunits Located in Neighboring Cells
*Center for Research & Advanced Studies, Department of Physiology, Biophysics and Neurosciences, Mexico City 07300, México;
University College of London, Institute of Ophthalmology, Department of Cell Biology, London WC1E 6BT, United Kingdom
Monitoring Editor: Keith Mostov
The polarized distribution of Na+,K+-ATPase plays a paramount physiological role, because either directly or through coupling with coand countertransporters, is responsible for the net movement of glucose, aminoacids, Ca2+, K+, Cl-, CO3H-, etc. across the whole epithelium. We report here that the
-subunit is a key factor in the polarized distribution of this enzyme. (1) MDCK cells (epithelial from dog kidney) express the Na+,K+-ATPase over the lateral side, but not on the basal domain, as if the contact with a neighboring cell were crucial for the specific membrane location of this enzyme. (2) MDCK cells cocultured with other epithelial types (derived from human, cat, dog, pig, monkey, rabbit, mouse, hamster and rat) express the enzyme in all (100%) homotypic MDCK/MDCK borders, but rarely in heterotypic ones. (3) Although MDCK cells never express Na+,K+-ATPase at contacts with Chinese hamster ovary (CHO) cells (CHO), they do when CHO cells are transfected with
1-subunit from the dog kidney (CHO-
). (4) This may be attributed to the adhesive property of the
1-subunit, as an aggregation assay using CHO (mock transfected) and CHO-
cells, shows that the expression of dog
1-subunit in the plasma membrane does increase adhesiveness. (5) This adhesiveness does not involve adherens nor tight junctions. (6) Transfection of
1-subunit forces CHO-
cells to coexpress endogenous
-subunit. Taken together, our results indicate that MDCK cells express Na+,K+-ATPase at a given border provided the contacting cell expresses the dog
1-subunit. The cell-cell interaction thus established would suffice to account for the polarized expression and positioning of the Na+,K+-ATPase in epithelial cells.
Corresponding author.
E-mail: shoshani{at}fisio.cinvestav.mx
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