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

Background & Aims: 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+](l)) 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 I-125 efflux and in individual 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 I-125 efflux approximately threefold above basal levels. Exposure to extracellular (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 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.