URSODEOXYCHOLATE INCREASES CYTOSOLIC CALCIUM-CONCENTRATION AND ACTIVATES CL- CURRENTS IN A BILIARY CELL-LINE

Background & Aims: Ursodeoxycholate (UDC) stimulates a bicarbonate-ric h choleresis, but the cellular mechanisms involved are not fully estab lished. Because ductular secretion also increases biliary HCO3- concen tration, the purpose of this study was to evaluate whether UDC has dir ect effects on duct cells by measuring intracellular calcium concentra tion ([Ca2+](l)) and membrane Cl- permeability in Mz-ChA-1 human chola ngiocarcinoma cells. Methods: Intracellular calcium levels were measur ed using fura-2 fluorescence, Membrane Cl- permeability was assessed i n subconfluent monolayers using I-125 efflux and in individual cells u sing 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 t o release of Ca2+ from intracellular stores and stimulated I-125 efflu x approximately threefold above basal levels. Exposure to extracellula r (1.25 mmol/L) or intracellular (100 mu mol/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 inhib ited by chelation of intracellular calcium, Conclusions: UDC in pharma cological concentrations increases [Ca2+](i) and stimulates Cl- efflux through opening of Cl- channels in biliary cells. We speculate that U DC could increase bile flow by direct stimulation of ductular secretio n and may be of therapeutic benefit to patients with cystic fibrosis w ho have impaired adenosine 3',5'-cyclic monophosphate-dependent biliar y secretion.