Identification of an apical Cl-/HCO3- exchanger in gastric surface mucous and duodenal villus cells.
The molecular identity of the apical HCO3(-)-secreting transporter in gastric mucous cells remains unknown despite its essential role in preventing injury and ulcer by gastric acid. Here we report the identification of a Cl-/HCO3- exchanger that is located on apical membranes of gastric surface epithelial cells. RT-PCR studies of mouse gastrointestinal tract mRNAs demonstrated that this transporter, known as anion exchanger isoform 4 (AE4), is expressed in both stomach and duodenum. Northern blot analysis of RNA from purified stomach epithelial cells indicated that AE4 is expressed at higher levels in mucous cells than in parietal cells. Immunoblotting experiments identified AE4 as a approximately 110- to 120-kDa protein in membranes from stomach epithelium and apical membranes from duodenum. Immunocytochemical staining demonstrated that AE4 is expressed in apical membranes of surface cells in both mouse and rabbit stomach and duodenum. Functional studies in oocytes indicated that AE4 functions as a Cl-/HCO3- exchanger. These data show that AE4 is an apical Cl-/HCO3- exchanger in gastric mucous cells and duodenal villus cells. On the basis of its function and location, we propose that AE4 may play an important role in mucosal protection.
Xu
Jie
J
Department of Medicine, University of Cincinnati, Cincinnati, Ohio 45267, USA.
Barone
Sharon
S
Petrovic
Snezana
S
Wang
Zhaohui
Z
Seidler
Ursula
U
Riederer
Brigitte
B
Ramaswamy
Krishnamurthy
K
Dudeja
Pradeep K
PK
Shull
Gary E
GE
Soleimani
Manoocher
M
D000818:Animals; D002462:Cell Membrane / Q000378:metabolism; D027963:Chloride-Bicarbonate Antiporters / Q000235:genetics / Q000378:metabolism*; D004386:Duodenum / Q000166:cytology / Q000378:metabolism*; D005753:Gastric Mucosa / Q000378:metabolism*; D006801:Humans; D051379:Mice; D008871:Microvilli / Q000378:metabolism; D012333:RNA, Messenger / Q000378:metabolism; D011817:Rabbits; D027982:Sodium-Bicarbonate Symporters
D027963:Chloride-Bicarbonate Antiporters; D012333:RNA, Messenger; C440068:SLC4A9 protein, human; C480025:Slc4a9 protein, mouse; D027982:Sodium-Bicarbonate Symporters