title: Apical NA+/H+ exchangers in the mammalian gastrointestinal tract.
abstract: The Slc9a family of nine Na(+)/H(+) exchangers (NHE) plays a critical role in neutral sodium absorption in the mammalian intestine as well as other absorptive and secretory epithelia of digestive organs. These transport proteins mediate the electroneutral exchange of Na(+) and H(+) and are crucial in a variety of physiological processes, including the fine tuning of intracellular pH, cell volume control and systemic electrolyte, acid-base and fluid volume homeostasis. Here, we review the role of the Na(+)/H(+) exchange mechanism as it relates to the physiology of organs and cells involved in nutrient absorption, and we describe physiological and molecular aspects of individual isoforms, including their structure, tissue-, and subcellular distribution, as well as their regulation by physiological stimuli at the transcriptional and post-transcriptional levels. A particular emphasis is placed on Na(+)/H(+) exchanger isoforms expressed on the apical (brush border) membrane of the epithelial cells, and the consequences of gene-targeted mutation of individual isoforms are discussed in the context of the physiology of digestive organs. Where available, we also provide a review of pathophysiological states related to aberrant expression and/or activity of Na(+)/H(+) exchangers within the confines of the digestive system.
authors.affiliation: Department of Pediatrics, Steele Children's Research Center, University of Arizona Health Sciences Center, Tucson, Arizona 85724, USA. pkiela@peds.arizona.edu
authors.forename: P R
authors.initials: PR
authors.lastname: Kiela
authors.forename: H
authors.initials: H
authors.lastname: Xu
authors.forename: F K
authors.initials: FK
authors.lastname: Ghishan
mesh_terms: D000818:Animals; D041981:Gastrointestinal Tract / Q000378:metabolism*; D006801:Humans; D008871:Microvilli / Q000378:metabolism; D017923:Sodium-Hydrogen Exchangers / Q000737:chemistry / Q000378:metabolism*
chemical_list: D017923:Sodium-Hydrogen Exchangers