title: AE4 is a DIDS-sensitive Cl(-)/HCO(-)(3) exchanger in the basolateral membrane of the renal CCD and the SMG duct.
abstract: The renal cortical collecting duct (CCD) plays an important role in systemic acid-base homeostasis. The beta-intercalated cells secrete most of the HCO(-)(3), which is mediated by a luminal, DIDS-insensitive, Cl(-)/HCO(-)(3) exchange. The identity of the luminal exchanger is a matter of debate. Anion exchanger isoform 4 (AE4) cloned from the rabbit kidney was proposed to perform this function (Tsuganezawa H et al. J Biol Chem 276: 8180-8189, 2001). By contrast, it was proposed (Royaux IE et al. Proc Natl Acad Sci USA 98: 4221-4226, 2001) that pendrin accomplishes this function in the mouse CCD. In the present work, we cloned, localized, and characterized the function of the rat AE4. Northern blot and RT-PCR showed high levels of AE4 mRNA in the CCD. Expression in HEK-293 and LLC-PK(1) cells showed that AE4 is targeted to the plasma membrane. Measurement of intracellular pH (pH(i)) revealed that AE4 indeed functions as a Cl(-)/HCO(-)(3) exchanger. However, AE4 activity was inhibited by DIDS. Immunolocalization revealed species-specific expression of AE4. In the rat and mouse CCD and the mouse SMG duct AE4 was in the basolateral membrane. By contrast, in the rabbit, AE4 was in the luminal and lateral membranes. In both, the rat and rabbit CCD AE4 was in alpha-intercalated cells. Importantly, localization of AE4 was not affected by the systemic acid-base status of the rats. Therefore, we conclude that expression and possibly function of AE4 is species specific. In the rat and mouse AE4 functions as a Cl(-)/HCO(-)(3) exchanger in the basolateral membrane of alpha-intercalated cells and may participate in HCO(-)(3) absorption. In the rabbit AE4 may contribute to HCO(-)(3) secretion.
authors.affiliation: Department of Physiology, Division of Nephrology, University of Texas Southwestern Medical Center, Dallas, TX 75390, USA.
authors.forename: Shigeru B H
authors.initials: SB
authors.lastname: Ko
authors.forename: Xiang
authors.initials: X
authors.lastname: Luo
authors.forename: Henrik
authors.initials: H
authors.lastname: Hager
authors.forename: Alexandra
authors.initials: A
authors.lastname: Rojek
authors.forename: Joo Young
authors.initials: JY
authors.lastname: Choi
authors.forename: Christoph
authors.initials: C
authors.lastname: Licht
authors.forename: Makoto
authors.initials: M
authors.lastname: Suzuki
authors.forename: Shmuel
authors.initials: S
authors.lastname: Muallem
authors.forename: Søren
authors.initials: S
authors.lastname: Nielsen
authors.forename: Kenichi
authors.initials: K
authors.lastname: Ishibashi
mesh_terms: D017878:4,4'-Diisothiocyanostilbene-2,2'-Disulfonic Acid / Q000494:pharmacology*; D000136:Acid-Base Equilibrium / Q000502:physiology; D000818:Animals; D002460:Cell Line; D002462:Cell Membrane / Q000378:metabolism; D027963:Chloride-Bicarbonate Antiporters / Q000096:biosynthesis* / Q000187:drug effects / Q000235:genetics*; D003001:Cloning, Molecular; D006801:Humans; D007150:Immunohistochemistry; D007668:Kidney / Q000166:cytology / Q000378:metabolism*; D007685:Kidney Tubules, Collecting / Q000378:metabolism; D018374:LLC-PK1 Cells; D051379:Mice; D008969:Molecular Sequence Data; D009928:Organ Specificity; D012333:RNA, Messenger / Q000096:biosynthesis; D011817:Rabbits; D051381:Rats; D016415:Sequence Alignment; D017386:Sequence Homology, Amino Acid; D027982:Sodium-Bicarbonate Symporters; D013045:Species Specificity; D013363:Submandibular Gland / Q000378:metabolism*; D013552:Swine
chemical_list: D027963:Chloride-Bicarbonate Antiporters; D012333:RNA, Messenger; C440068:SLC4A9 protein, human; D027982:Sodium-Bicarbonate Symporters; C466138:anion exchange protein 4, rat; D017878:4,4'-Diisothiocyanostilbene-2,2'-Disulfonic Acid