title: NH4Cl activates AE2 anion exchanger in Xenopus oocytes at acidic pHi.
abstract: In the course of experiments to define regulation by intracellular pH (pHi) of the AE2 anion exchanger expressed in Xenopus oocytes, we discovered an unexpected regulation of AE2 by NH4+. Intracellular acidification produced by extracellular acidification or produced by equimolar substitution of NaCl with sodium acetate each inhibited AE2 activity. In contrast, intracellular acidification by equimolar substitution of NaCl with NH4Cl activated AE2-associated, trans-anion-dependent, 4,4'-diisothiocyanostilbene-2,2'-disulfonic acid-sensitive 36Cl- influx and efflux. Regulation by NH4+ was isoform specific, since neither erythroid nor kidney AE1 was activated. AE2 activation was maximal at <5 mM NH4Cl; was not mimicked by extracellular KCl, chloroquine, or polyamines; and was insensitive to amiloride, bumetanide, barium, and gadolinium. Whether NH4Cl acts directly on AE2 or on another target remains to be determined. Activation of AE2 by NH4+ may serve to sustain Cl-/HCO3- exchange activity in the presence of acidic pH in renal medulla, colon, abscesses, and other AE2-expressing acidic locales exposed to elevated NH4+ concentration.
authors.affiliation: Department of Medicine, Harvard Medical School, Beth Israel Hospital, Boston, Massachusetts 02215, USA.
authors.forename: B D
authors.initials: BD
authors.lastname: Humphreys
authors.forename: M N
authors.initials: MN
authors.lastname: Chernova
authors.forename: L
authors.initials: L
authors.lastname: Jiang
authors.forename: Y
authors.initials: Y
authors.lastname: Zhang
authors.forename: S L
authors.initials: SL
authors.lastname: Alper
mesh_terms: D000143:Acids / Q000378:metabolism*; D000468:Alkalies / Q000378:metabolism; D000643:Ammonium Chloride / Q000494:pharmacology*; D000818:Animals; D027321:Anion Transport Proteins; D017920:Antiporters; D004594:Electrophysiology; D005260:Female; D006863:Hydrogen-Ion Concentration; D007536:Isomerism; D008565:Membrane Proteins / Q000378:metabolism*; D051379:Mice; D009865:Oocytes / Q000166:cytology / Q000378:metabolism* / Q000502:physiology; D015388:Organelles / Q000378:metabolism; D011073:Polyamines / Q000494:pharmacology; D064606:SLC4A Proteins; D019346:Sodium Acetate / Q000494:pharmacology; D017923:Sodium-Hydrogen Exchangers / Q000378:metabolism; D014981:Xenopus / Q000378:metabolism*
chemical_list: D000143:Acids; D000468:Alkalies; D027321:Anion Transport Proteins; D017920:Antiporters; D008565:Membrane Proteins; D011073:Polyamines; D064606:SLC4A Proteins; D017923:Sodium-Hydrogen Exchangers; D000643:Ammonium Chloride; D019346:Sodium Acetate