Identification and functional characterization of TMEM16A, a Ca2+-activated Cl- channel activated by extracellular nucleotides, in biliary epithelium.
Cl(-) channels in the apical membrane of biliary epithelial cells (BECs) provide the driving force for ductular bile formation. Although a cystic fibrosis transmembrane conductance regulator has been identified in BECs and contributes to secretion via secretin binding basolateral receptors and increasing [cAMP](i), an alternate Cl(-) secretory pathway has been identified that is activated via nucleotides (ATP, UTP) binding apical P2 receptors and increasing [Ca(2+)](i). The molecular identity of this Ca(2+)-activated Cl(-) channel is unknown. The present studies in human, mouse, and rat BECs provide evidence that TMEM16A is the operative channel and contributes to Ca(2+)-activated Cl(-) secretion in response to extracellular nucleotides. Furthermore, Cl(-) currents measured from BECs isolated from distinct areas of intrahepatic bile ducts revealed important functional differences. Large BECs, but not small BECs, exhibit cAMP-stimulated Cl(-) currents. However, both large and small BECs express TMEM16A and exhibit Ca(2+)-activated Cl(-) efflux in response to extracellular nucleotides. Incubation of polarized BEC monolayers with IL-4 increased TMEM16A protein expression, membrane localization, and transepithelial secretion (I(sc)). These studies represent the first molecular identification of an alternate, noncystic fibrosis transmembrane conductance regulator, Cl(-) channel in BECs and suggest that TMEM16A may be a potential target to modulate bile formation in the treatment of cholestatic liver disorders.
Department of Pediatrics, University of Texas Southwestern Medical Center at Dallas, Dallas, Texas 75390-9063, USA.
Amal K
AK
Dutta
Al-karim
AK
Khimji
Charles
C
Kresge
Abhijit
A
Bugde
Michael
M
Dougherty
Victoria
V
Esser
Yoshiyuki
Y
Ueno
Shannon S
SS
Glaser
Gianfranco
G
Alpini
Don C
DC
Rockey
Andrew P
AP
Feranchak
D000818:Animals; D000075369:Anoctamin-1; D001646:Bile / Q000378:metabolism; D001659:Biliary Tract / Q000166:cytology* / Q000187:drug effects; D002463:Cell Membrane Permeability / Q000187:drug effects; D018118:Chloride Channels; D002713:Chlorine / Q000378:metabolism; D004848:Epithelium / Q000187:drug effects / Q000378:metabolism; D005110:Extracellular Space / Q000187:drug effects / Q000378:metabolism*; D005786:Gene Expression Regulation / Q000187:drug effects; D006801:Humans; D015847:Interleukin-4 / Q000494:pharmacology; D008565:Membrane Proteins / Q000235:genetics / Q000378:metabolism*; D051379:Mice; D009363:Neoplasm Proteins / Q000235:genetics / Q000378:metabolism*; D009711:Nucleotides / Q000378:metabolism*; D012333:RNA, Messenger / Q000235:genetics / Q000378:metabolism; D051381:Rats
C476213:ANO1 protein, human; D000075369:Anoctamin-1; D018118:Chloride Channels; D008565:Membrane Proteins; D009363:Neoplasm Proteins; D009711:Nucleotides; D012333:RNA, Messenger; D015847:Interleukin-4; D002713:Chlorine