Determinants of Cell Surface Distributions of Na+/K+ ATPase in Polarized Epithelial Cells

Abstract

While there has been emphasis in recent years on understanding the protein structure, catalytic function and assembly of Na+/K+-ATPase (23), relatively less attention has been given to the mechanisms involved in regulating restricted distributions of Na+/K+-ATPase on the plasma membrane of cells. The function of Na+/K+-ATPase is to maintain plasma membrane potential, cell volume and, in general, cellular homeostasis; this requires that functional protein is expressed at the cell surface. However,in transporting epithelia, localization of Na+/K+-ATPase to the cell surface alone is not sufficient for cellular function (1). These cells play critical roles in regulating the ionic composition of biological compartments that are separated by the epithelium. In the kidney, for example, the renal tubule comprises a closed monolayer of cells that regulate the vectorial transport (reabsorption) of ions and solutes from the lumen of the tubule to the blood supply. In contrast, in the choroid plexus the epithelium controls vectorial transport (secretion) from the blood supply to the ventricular space to form the cerebral-spinal fluid. Opposite directions of ion transport across transporting epithelium is determined by the distribution of ion channels, exchanges and transporters between domains of the plasma membrane that face different biological compartments; these domains are defined as apical (facing the lumen or closed compartment) and basal-lateral (facing the blood supply) [see Figure 1]. Defining the mechanisms involved in regulating the distributions of these proteins is central to our understanding of the function of this important cell type in normal and disease states.KeywordsApical MembraneMDCK CellChoroid PlexusMembrane DomainVectorial TransportThese keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.