Ursodeoxycholate increases cytosolic calcium concentration and activates Cl- currents in a biliary cell line.
OBJECTIVE
Ursodeoxycholate (UDC) stimulates a bicarbonate-rich choleresis, but the cellular mechanisms involved are not fully established. Because ductular secretion also increases biliary HCO3-concentration, the purpose of this study was to evaluate whether UDC has direct effects on duct cells by measuring intracellular calcium concentration ([Ca2+]i) and membrane Cl- permeability in Mz-ChA-1 human cholangiocarcinoma cells.


METHODS
Intracellular calcium levels were measured using fura-2 fluorescence. Membrane Cl- permeability was assessed in subconfluent monolayers using 125I efflux and in individuals cells using whole-cell patch clamp techniques.


RESULTS
Exposure to UDC (2.5 mmol/L) increased [Ca2+]i from 180 +/- 25 to 639 +/- 84 nmol/L due to release of Ca2+ from intracellular stores and stimulated 125I efflux approximately threefold above basal levels. Exposure to extracellular (1.25 mmol/L) or intracellular (100 mumol/L) UDC activated currents carried by Cl- ions; intracellular UDC increased current density from 4.7 +/- 1.3 to 32.5 +/- 8.8 pA/pF. UDC-stimulated currents were inhibited by chelation of intracellular calcium.


CONCLUSIONS
UDC in pharmacological concentrations increases [Ca2+]i and stimulates Cl- efflux through opening of Cl- channels in biliary cells. We speculate that UDC could increase bile flow by direct stimulation of ductular secretion and may be of therapeutic benefit to patients with cystic fibrosis who have impaired adenosine 3',5'-cyclic monophosphate-dependent biliary secretion.
Shimokura
G H
GH
Department of Medicine, Duke University Medical Center, Durham, North Carolina, USA.
McGill
J M
JM
Schlenker
T
T
Fitz
J G
JG
D001650:Bile Duct Neoplasms / Q000378:metabolism* / Q000473:pathology; D002118:Calcium / Q000378:metabolism*; D002463:Cell Membrane Permeability / Q000187:drug effects; D018118:Chloride Channels / Q000187:drug effects / Q000378:metabolism*; D018281:Cholangiocarcinoma / Q000378:metabolism* / Q000473:pathology; D003600:Cytosol / Q000187:drug effects / Q000378:metabolism; D006801:Humans; D008564:Membrane Potentials / Q000187:drug effects; D018408:Patch-Clamp Techniques; D014407:Tumor Cells, Cultured / Q000187:drug effects / Q000378:metabolism; D014580:Ursodeoxycholic Acid / Q000494:pharmacology*
D018118:Chloride Channels; D014580:Ursodeoxycholic Acid; D002118:Calcium