title: H(+)/solute-induced intracellular acidification leads to selective activation of apical Na(+)/H(+) exchange in human intestinal epithelial cells.
abstract: The intestinal absorption of many nutrients and drug molecules is mediated by ion-driven transport mechanisms in the intestinal enterocyte plasma membrane. Clearly, the establishment and maintenance of the driving forces - transepithelial ion gradients - are vital for maximum nutrient absorption. The purpose of this study was to determine the nature of intracellular pH (pH(i)) regulation in response to H(+)-coupled transport at the apical membrane of human intestinal epithelial Caco-2 cells. Using isoform-specific primers, mRNA transcripts of the Na(+)/H(+) exchangers NHE1, NHE2, and NHE3 were detected by RT-PCR, and identities were confirmed by sequencing. The functional profile of Na(+)/H(+) exchange was determined by a combination of pH(i), (22)Na(+) influx, and EIPA inhibition experiments. Functional NHE1 and NHE3 activities were identified at the basolateral and apical membranes, respectively. H(+)/solute-induced acidification (using glycylsarcosine or beta-alanine) led to Na(+)-dependent, EIPA-inhibitable pH(i) recovery or EIPA-inhibitable (22)Na(+) influx at the apical membrane only. Selective activation of apical (but not basolateral) Na(+)/H(+) exchange by H(+)/solute cotransport demonstrates that coordinated activity of H(+)/solute symport with apical Na(+)/H(+) exchange optimizes the efficient absorption of nutrients and Na(+), while maintaining pH(i) and the ion gradients involved in driving transport.
authors.affiliation: Department of Physiological Sciences, Medical School, University of Newcastle upon Tyne, Newcastle upon Tyne NE2 4HH, United Kingdom. d.t.thwaites@ncl.ac.uk
authors.forename: D T
authors.initials: DT
authors.lastname: Thwaites
authors.forename: D
authors.initials: D
authors.lastname: Ford
authors.forename: M
authors.initials: M
authors.lastname: Glanville
authors.forename: N L
authors.initials: NL
authors.lastname: Simmons
mesh_terms: D000230:Adenocarcinoma / Q000473:pathology; D016764:Cell Polarity; D003110:Colonic Neoplasms / Q000473:pathology; D004847:Epithelial Cells / Q000378:metabolism; D005766:Gastrointestinal Contents; D006801:Humans; D006863:Hydrogen-Ion Concentration; D007413:Intestinal Mucosa / Q000378:metabolism*; D017136:Ion Transport; D009363:Neoplasm Proteins / Q000096:biosynthesis / Q000235:genetics; D020033:Protein Isoforms / Q000096:biosynthesis* / Q000235:genetics; D011522:Protons; D012333:RNA, Messenger / Q000096:biosynthesis; D012334:RNA, Neoplasm / Q000096:biosynthesis; D020133:Reverse Transcriptase Polymerase Chain Reaction; D012964:Sodium / Q000378:metabolism*; D000074083:Sodium-Hydrogen Exchanger 3; D017923:Sodium-Hydrogen Exchangers / Q000096:biosynthesis* / Q000235:genetics; D014407:Tumor Cells, Cultured
chemical_list: D009363:Neoplasm Proteins; D020033:Protein Isoforms; D011522:Protons; D012333:RNA, Messenger; D012334:RNA, Neoplasm; C081517:SLC9A2 protein, human; C000613385:SLC9A3 protein, human; D000074083:Sodium-Hydrogen Exchanger 3; D017923:Sodium-Hydrogen Exchangers; C069139:growth factor-activatable Na-H exchanger NHE-1; D012964:Sodium