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

Abstract

Background & Aims: The molecular mechanisms that contribute to the cholestatic condition in hepatocytes are poorly defined. It has been postulated that a disruption of normal vesicle-based protein trafficking may lead to alterations in hepatocyte polarity. Methods: To determine if vesicle motility is reduced by cholestasis, hepatocytes cultured from livers of bile duct ligation (BDL)– or ethinyl estradiol (EE)–injected rats, were viewed and recorded by high-resolution video microscopy. Cholestatic hepatocytes were analyzed by phalloidin staining and electron microscopy. Functional analysis was done by the sodium fluorescein sequestration assay. Results: In cholestatic hepatocytes, there was a significant decrease in the number of motile cytoplasmic vesicles observed compared with control cells. Further examination of cells from BDL- or EE-treated livers revealed the presence of numerous 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 those seen about bile canaliculi. Electron microscopy revealed that these structures were lined by actin-filled microvilli. Further, these pseudocanaliculi perform many of the functions exhibited by bona fide canaliculi, such as sequestering sodium fluorescein. Conclusions: Both mechanically and chemically induced cholestasis have substantial effects on vesicle-based transport, leading to marked disruption of hepatocellular polarity.GASTROENTEROLOGY 2001;121:1176-1184