Characterization of Volume-Activated Chloride Currents in Regulatory Volume Decrease of Human Cholangiocyte |
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Authors: | Biyi Chen Douglas M Jefferson Won Kyoo Cho |
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Institution: | (1) Department of Medicine, Division of Gastroenterology/Hepatology, Indiana University School of Medicine and The Richard L. Roudebush Veterans Affairs Medical Center, 1481 W 10th Street, Indianapolis, IN 46202, USA;(2) Department of Physiology, Tufts University School of Medicine and Departments of Pediatrics and Medicine, Tufts Medical Center, Boston, MA 02111, USA;(3) Department of Cellular and Integrative Physiology, Indiana University School of Medicine, Indianapolis, IN 46202, USA; |
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Abstract: | Volume-activated chloride channel (VACC) plays vital roles in many physiological functions. In bile duct epithelium, VACC
actively participates in biliary secretion and cell volume regulation, and it mediates regulatory volume decrease (RVD). Recently,
we have shown that mouse cholangiocytes have an intact RVD via VACC and K+ conductance. However, such cell volume regulation was not studied in the normal human cholangiocyte. Volume measurement by
Coulter counter and whole-cell patch clamp technique were used to characterize the RVD and VACC in human cholangiocyte cell
line (HBDC). When exposed to hypotonic solution, HBDC exhibited an intact RVD, which was inhibited by 1,2-Bis(2-aminophenoxy)ethane-N,N,N′,N′-tetraacetic
acid tetrakis(acetoxymethyl ester) (BAPTA-AM), NPPB (5-nitro-2′- (3-phenylpropylamino)-benzoate), DIDS (4,4′-diisothiocyanatostilbene-2-disulfonic
acid), and tamoxifen, but was not affected by the removal of extracellular calcium. During RVD, HBDC exhibited large, outwardly
rectifying currents and time-dependent inactivation at positive potential. The amplitude of the outward current was approximately
3 times of that of the inward current, and this volume-activated current returned to the baseline when switched to isotonic
solution. The amplitude and reversal potential of the volume-activated current was dependent on Cl− concentration, and the VACC was significantly inhibited by replacing chloride with gluconate, glutamate, sucrose, and acetate
in the hypotonic solution. In addition, classical VACC inhibitors, such as NPPB or tamoxifen, inhibited the VACC. These inhibitory
effects were reversible with washing out the inhibitors from the bath solution. The present study is the first to characterize
and show that HBDC has an intact RVD, mediated by VACC, which has similar electrophysiological characteristics as that in
mouse cholangiocytes. |
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