Alterations in vesicle transport and cell polarity in rat hepatocytes subjected to mechanical or chemical cholestasis

Background & Aims. The molecular mechanisms that contribute to the cholesta tic condition in hepatocytes are poorly defined. It has been postulated tha t a disruption of normal vesicle-based protein trafficking may lead. to alt erations in hepatocyte polarity. Methods: To determine if vesicle motility is reduced by cholestasis, hepatocytes cultured from livers of bile duct li gation (BDL)or ethinyl estradiol (EE)-injected rats, were viewed and record ed by high-resolution video microscopy. Cholestatic hepatocytes were analyz ed by phalloidin staining and electron microscopy. Functional analysis was done by the sodium fluorescein sequestration. assay. Results: In cholestati c hepatocytes, there was a significant decrease in. the number of motile cy toplasmic, vesicles observed compared with control cells. Further examinati on of cells from BDL- or EE-treated livers revealed the presence of numerou s large intracellular lumina. More than 24% of cells in BDL-treated livers and 19% of cells in EE-treated livers displayed these structures, compared with 1.1% found in control hepatocytes. Phalloidin staining of hepatocytes showed a prominent sheath of actin surrounding the lumina, reminiscent of t hose seen about bile canaliculi. Electron microscopy revealed that these st ructures were lined by actin-filled microvilli. Further, these pseudocanali culi perform many of the functions exhibited by bona fide canaliculi, such as sequestering sodium fluorescein. Conclusions. Both mechanically and chem ically induced cholestasis have substantial effects on vesicle-based transp ort, leading to marked disruption of hepatocellular polarity.