The involvement of altered vesicle transport in redistribution of Ca2+, Mg2+-ATPase in cholestatic rat liver

Vectorial sorting of plasma membrane protein-containing vesicles is essenti al for the establishment and maintenance of cell polarity. In the present s tudy, the involvement of altered vesicle transport in the redistribution of membrane-bound Ca2+, Mg2+-ATPase resulting from cholestasis was investigat ed in hepatocytes. Cholestasis was induced in rat liver by common bile duct ligation. Ca2+, Mg2+-ATPase activity was demonstrated histochemically at t he light and electron microscopical levels. Microtubules, an important fact or for transcellular transport of vesicles, were studied in situ by immunof luorescence microscopy and electron microscopy in detergent-extracted prepa rations. The results showed that microtubules underwent significant changes after common bile duct ligation. The most pronounced alteration was focal accumulation of beta-tubulin in the cytoplasm of hepatocytes after 7 days o f common bile duct ligation. At the electron microscopical level, the numbe r of microtubules was increased considerably. in control livers, the activi ty of Ca2+, Mg2+-ATPase was localized only at the apical plasma membrane of hepatocytes, bur it was also present at the basolateral plasma membrane af ter common bile duct ligation. The number of intracellular vesicles contain ing Ca2+, Mg2+-ATPase activity was increased strikingly, and some of them w ere associated with lateral membrane domains in which Ca2+, Mg2+-ATPase act ivity was found. It is concluded that common bile duct ligation induces the rearrangement of microtubules, which may disturb vectorial transport of Ca 2+, Mg2+-ATPase-containing vesicles in hepatocytes, leading to the redistri bution of Ca2+, Mg2+-ATPase. (C) 1998 Chapman & Hall.