Efficient In Vitro vectorial transport of a fluorescent conjugated bile acid analogue by polarized hepatic hybrid WIF-B and WIF-B9 cells

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Abstract
Efficient transport of bile acids, a typical characteristic of hepatocytes, is partially lost in most hepatoma cell lines and in normal hepatocytes after some days in culture. We have tested whether the polarized rat hepatoma-human fibroblast hybrid WIF (hybrids between W138 and Fao cells) cells previously obtained by our group were able to perform vectorial transport of the fluorescent bile acid derivative cholylglycylamidofluorescein (CGamF) towards the bile canaliculi (BC). Four different WIF clones were analyzed. All were well polarized, as shown by the formation of spherical and even tubular BC-like structures and by the restricted localization at the BC, visualized by immunofluorescence, of the apical membrane marker HA4, a possible bile acid carrier. WIF-B and its subclone WIF-B9 were found to accumulate CGamF in 65% to 75% of their BC. This transport was time, temperature, and partly sodium dependent and was inhibited by coincubation with the parental natural bile salt cholylglycine. Dinitrophenyl glutathione, a substrate of the canalicular multispecific organic anion transporter, did not inhibit CGamF canalicular secretion, whereas it greatly impaired the canalicular secretion of a non-bile acid organic anion, fluorescein, generated intracellularly from fluorescein diacetate. Confocal microscopy confirmed the presence of CGamF in the cytoplasm, supporting a transcellular route from medium to BC. In contrast, two other polarized clones exhibited a poor ability (WIF 12-6) or no ability (WIF12-1 TGδ) to vectorially transport CGamF. In conclusion, WIF-B and WIF-B9 exhibit not only structural but also functional polarity, at least as far as vectorial organic anion transport is concerned.

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