title: Expression of anion exchangers in cultured human endolymphatic sac epithelia.
abstract: OBJECTIVE
  Pendrin acts as a Cl-/HCO3- exchanger and is responsible for endolymphatic fluid volume and pH homeostasis in human endolymphatic sac epithelial cells.
  
  
  BACKGROUND
  The endolymphatic sac (ES) is part of the membranous labyrinth in the inner ear that plays an important role in maintaining homeostasis of the endolymphatic fluid system. However, the exact mechanism of fluid volume and pH regulation is not fully understood yet. We aimed to demonstrate the expression of various anion exchangers (AEs), including pendrin, in cultured human endolymphatic sac epithelial (HESE) cells.
  
  
  METHODS
  Endolymphatic sac specimens were harvested during acoustic neuroma surgery (n = 24) using the translabyrinthine approach and then subcultured with high epidermal growth factor (EGF) (25 ng/ml) media and differentiated using low-EGF (0.5 ng/ml) media. The cultured cells were classified according to the morphology on TEM. The Cl-/HCO3- exchanger activity was assessed by pHi measurement using pH sensitive dye 2', 7'-bis (2-carboxyethyl)-5(6)-carboxyfluorescein (BCECF/AM). We performed reverse transcriptase-polymerase chain reaction and immunohistochemical staining for AEs.
  
  
  RESULTS
  We determined that 7.3 ± 6.7% of cells differentiated into mitochodria-rich cells and 50.2 ± 15.1 of cells differentiated into ribosome-rich cells. bAE3, AE4, SLC26A4, SLC26A6, and SLC26A11 were also expressed in cultured HESE cells. The cultured cells had Cl-/HCO3- and Cl-/formate exchange activity on the luminal membrane, which is sensitive to anion channel inhibitors (DIDS 500 μM). Furthermore, we showed that pendrin (SLC26A4) was expressed in cultured HESE cell membranes.
  
  
  CONCLUSIONS
  Our results suggest that AEs, including pendrin, are expressed in epithelia of ES and may have role in maintaining ionic homeostasis, and the HESE culture system are useful for uncovering the functional role of ES epithelial cells.
authors.affiliation: Brain Korea 21 Project for Medical Science, Yonsei University College of Medicine, Seoul, Republic of Korea.
authors.forename: Hyun Jae
authors.initials: HJ
authors.lastname: Lee
authors.forename: Won Sun
authors.initials: WS
authors.lastname: Yang
authors.forename: Hyun Woo
authors.initials: HW
authors.lastname: Park
authors.forename: Hyun Seung
authors.initials: HS
authors.lastname: Choi
authors.forename: Sung Huhn
authors.initials: SH
authors.lastname: Kim
authors.forename: Jin Young
authors.initials: JY
authors.lastname: Kim
authors.forename: Jae Young
authors.initials: JY
authors.lastname: Choi
mesh_terms: D017878:4,4'-Diisothiocyanostilbene-2,2'-Disulfonic Acid / Q000494:pharmacology; D017920:Antiporters / Q000037:antagonists & inhibitors / Q000096:biosynthesis*; D002478:Cells, Cultured; D004712:Endolymphatic Sac / Q000166:cytology / Q000378:metabolism* / Q000648:ultrastructure; D004847:Epithelial Cells / Q000187:drug effects / Q000378:metabolism* / Q000648:ultrastructure; D006801:Humans; D006863:Hydrogen-Ion Concentration; D007150:Immunohistochemistry; D026901:Membrane Transport Proteins / Q000096:biosynthesis; D046529:Microscopy, Electron, Transmission; D008928:Mitochondria / Q000378:metabolism; D010641:Phenotype; D060888:Real-Time Polymerase Chain Reaction; D012270:Ribosomes / Q000378:metabolism; D000076988:Sulfate Transporters
chemical_list: D017920:Antiporters; D026901:Membrane Transport Proteins; C085609:SLC26A4 protein, human; D000076988:Sulfate Transporters; D017878:4,4'-Diisothiocyanostilbene-2,2'-Disulfonic Acid