title: Regulation of intestinal epithelial brush border Na(+)/H(+) exchanger isoforms, NHE2 and NHE3, in C2bbe cells.
abstract: Until recently, studies to characterize the intestinal epithelial Na(+)/H(+) exchangers had to be done in nonepithelial, mutated fibroblasts. In these cells, detection of any Na(+)/H(+) exchange activity requires prior acid loading. Furthermore, most of these experiments used intracellular pH changes to measure NHE activity. Because changes in pH(i) only approximate Na(+)/H(+) exchange activity, and may be confounded by alterations in buffering capacity and/or non-NHE contributions to pH regulation, we have used (22)[Na] unidirectional apical to cell uptake to measure activities specific to NHE2 or NHE3. Furthermore, we performed these measurements under basal, nonacid-stimulated conditions to avoid bias from this nonphysiological experimental precondition. Both brush border NHEs, when expressed in the well-differentiated, intestinal villuslike Caco-2 subclone, C2bbe (C2), localize to the C2 apical domain and are regulated by second messengers in the same way they are regulated in vivo. Increases in intracellular calcium and cAMP inhibit both isoforms, while phorbol ester affects only NHE3. NHE2 inhibition by cAMP and Ca(++) involves changes to both K(Na) and V(max). In contrast, the same two second messengers inhibit NHE3 by a decrease in V(max) exclusively. Phorbol ester activation of protein kinase C alters both V(max) and K(Na) of NHE3, suggesting a multilevel regulatory mechanism. We conclude that NHE2 and NHE3, in epithelial cells, are basally active and are differentially regulated by signal transduction pathways.
authors.affiliation: Division of Gastroenterology, Department of Medicine, University of Chicago, 5841 S. Maryland Ave., Chicago, IL 60637, USA.
authors.forename: C
authors.initials: C
authors.lastname: Bookstein
authors.forename: M W
authors.initials: MW
authors.lastname: Musch
authors.forename: Y
authors.initials: Y
authors.lastname: Xie
authors.forename: M C
authors.initials: MC
authors.lastname: Rao
authors.forename: E B
authors.initials: EB
authors.lastname: Chang
mesh_terms: D018938:Caco-2 Cells; D000242:Cyclic AMP / Q000378:metabolism; D004848:Epithelium / Q000187:drug effects / Q000378:metabolism; D006801:Humans; D006863:Hydrogen-Ion Concentration; D007413:Intestinal Mucosa / Q000378:metabolism*; D007422:Intestines / Q000187:drug effects; D007424:Intracellular Fluid / Q000378:metabolism; D007700:Kinetics; D008871:Microvilli / Q000187:drug effects / Q000378:metabolism*; D015398:Signal Transduction; D000074083:Sodium-Hydrogen Exchanger 3; D017923:Sodium-Hydrogen Exchangers / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism*; D013755:Tetradecanoylphorbol Acetate / Q000494:pharmacology; D014162:Transfection
chemical_list: C081517:SLC9A2 protein, human; C000613385:SLC9A3 protein, human; D000074083:Sodium-Hydrogen Exchanger 3; D017923:Sodium-Hydrogen Exchangers; D000242:Cyclic AMP; D013755:Tetradecanoylphorbol Acetate