Effect of ursodeoxycholic acid on intracellular pH in a bile duct epithelium-like cell line.
Recent studies in perfused livers and isolated hepatocytes indicate that ursodeoxycholic acid-induced HCO3-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-carboxyethyl)-5,6,carboxy fluorescein. Administration of 50 to 1,000 mumol/L UDCA in the absence of HCO3 caused dose-dependent intracellular acidification (intracellular pH = -0.13 +/- 0.03 pH/U after 500 mumol/L ursodeoxycholic acid). Acidification was not prevented by preincubation of cells with 0.5 mmol/L 4,4-diisothiocyanatostilbene-2,2,-disulfonic acid (DIDS) for 30 min or by furosemide administration (1 mmol/L), thus ruling out the stimulation of Cl/HCO3 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/HCO3 exchange) failed to show significative differences between cells treated with 500 mumol/L UDCA and controls.(ABSTRACT TRUNCATED AT 250 WORDS)
Strazzabosco
M
M
Istituto di Medicina Interna, Universitá di Padova, Italy.
Poci
C
C
Spirlí
C
C
Sartori
L
L
Knuth
A
A
Crepaldi
G
G
D000136:Acid-Base Equilibrium / Q000187:drug effects; D001639:Bicarbonates / Q000378:metabolism; D001650:Bile Duct Neoplasms / Q000378:metabolism / Q000473:pathology; D001652:Bile Ducts / Q000187:drug effects* / Q000378:metabolism / Q000473:pathology; D001653:Bile Ducts, Intrahepatic; D001692:Biological Transport; D018281:Cholangiocarcinoma / Q000378:metabolism / Q000473:pathology; D004058:Diffusion; D004848:Epithelium / Q000187:drug effects / Q000378:metabolism / Q000473:pathology; D006801:Humans; D006863:Hydrogen-Ion Concentration; D014407:Tumor Cells, Cultured / Q000187:drug effects / Q000378:metabolism; D014580:Ursodeoxycholic Acid / Q000494:pharmacology*
D001639:Bicarbonates; D014580:Ursodeoxycholic Acid