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.
