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Effect of ursodeoxycholic acid on intracellular pH in a bile duct epithelium‐like cell line
Author(s) -
Strazzabosco Mario,
Poci Carlo,
Spirlí Carlo,
Sartori Leonardo,
Knuth Alexander,
Crepaldi Gaetano
Publication year - 1994
Publication title -
hepatology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 5.488
H-Index - 361
eISSN - 1527-3350
pISSN - 0270-9139
DOI - 10.1002/hep.1840190124
Subject(s) - ursodeoxycholic acid , intracellular ph , dids , intracellular , bile acid , chemistry , biochemistry , medicine , membrane
Recent studies in perfused livers and isolated hepatocytes indicate that ursodeoxycholic acid‐induced HCO 3 ‐rich hypercholeresis originates at the ductule/duct level. The bile duct epithelium may be involved in bile alkalinization by passively reabsorbing the protonated unconjugated ursodeoxycholic acid, by directly secreting in response to an ursodeoxycholic acid‐induced increase in acid/base transporter activity or by taking up UDCA − in exchange for a base equivalent. To investigate these processes in more detail, we studied the effects of ursodeoxycholic acid on intracellular pH in SK‐ChA‐1, a well‐differentiated human cholangiocarcinoma cell line similar to bile duct epithelium in terms of intracellular pH regulatory mechanisms and morphological markers. Intracellular pH changes were monitored with a microfluorimetric setup using the fluorescent indicator 2′ −7′‐ bis (2‐car‐boxyethyl)−5, 6, carboxy fluorescein. Administration of 50 to 1,000 μmol/LUDCA in the absence of HCO 3 caused dose‐dependent intracellular acidification (intracellular pH = −0.13 ± 0.03 pH/U after 500 μmol/L ursodeoxycholic acid). Acidification was not prevented by preincubation of cells with 0.5 mmol/L 4,4‐diisothiocy‐anatostilbene‐2,2,‐disulfonic acid (DIDS) for 30 min or by furosemide administration (1 mmol/L), thus ruling out the stimulation of Cl/HCO 3 exchange or the presence of an ursodeoxycholic acid/base exchange. Ursodeoxycholic acid also acidified human fibroblasts, a cell type with no transport capability for ursodeoxycholic acid. In addition, direct measurement of the activities of the three major acid/base transporters in SK‐ChA‐1 cells (Na + /H + exchange, sodium‐dependent and sodium‐independent Cl/HCO 3 exchange) failed to show significative differences between cells treated with 500 μmol/L UDCA and controls. In conclusion, ursodeoxycholic acid administration does not primarily stimulate the activities of acid/base transporters responsible for HCO 3 secretion by bile duct epithelium. Rather, similar to what has previously been shown in hepatocytes, ursodeoxycholic acid induces intracellular acidification in SK‐ChA‐1 cells and in fibroblasts. This effect is likely mediated by nonionic diffusion of the weak acid ursodeoxycholic acid. These data confirm that ursodeoxycholic acid can be passively reabsorbed by the biliary epithelium, consistent with the cholehepatic‐shunt hypothesis. (Hepatology 1994;19:145–154).