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REVIEW

Unexpected Roles of the Na-K-ATPase and Other Ion Transporters in Cell Junctions and Tubulogenesis

Thomas Krupinski and Greg J. Beitel

Department of Biochemistry, Molecular Biology and Cell Biology, Northwestern University, Evanston, Illinois beitel{at}northwestern.edu

Recent work shows that transport-independent as well as transport-dependent functions of ion transporters, and in particular the Na-K-ATPase, are required for formation and maintenance of several intercellular junctions. Furthermore, these junctional and other nonjunctional functions of ion transporters contribute to development of epithelial tubes. Here, we consider what has been learned about the roles of ion pumps in formation of junctions and epithelial tubes in mammals, zebrafish, Drosophila, and C. elegans. We propose that asymmetric association of the Na-K-ATPase with cell junctions early in metazoan evolution enabled vectorial transcellular ion transport and control of intraorganismal environment. Ion transport-independent functions of the Na-K-ATPase arose as junctional complexes evolved.