STRUCTURAL AND FUNCTIONAL ALTERATIONS OF HEPATOCYTES DURING TRANSIENTPHALLOIDIN-INDUCED CHOLESTASIS IN THE RAT

To study the relationship between the dynamic actin web and bile secre tion, we developed an acute model of cholestasis, using phalloidin, an d examined sequential morphologic and biochemical events in rat liver. Biliary function (bile flow, bile, and canalicular membrane component s) and cellular integrity (release of hepatic enzymes in serum and bil e, canalicular structure, and microfilaments distribution) in rats giv en a single iv dose of phalloidin (0.8 mg/kg body weight) were assesse d at 15, 45, and 90 min, 24 hr, and 5 days postinjection. Bile flow de creased significantly at 45 and 90 min, but cholestasis was transient since bile secretion returned to control levels at 24 hr. The biliary bile acid secretion rate was not modified during the same time period, indicating that cholestasis may have been due to impairment of the bi le acid independent component of bile flow. Serum alanine aminotransfe rase and lactate dehydrogenase as well as biliary alkaline phosphatase and alkaline phosphodiesterase-1 activities were not altered by phall oidin treatment. These data, coupled with morphologic studies, provide no evidence of cell damage. Electron microscopy revealed that the per icanalicular actin web in both centrilobular and periportal hepatocyte s was increased at 90 min and further enlarged at 24 hr and 5 days aft er phalloidin injection. At all time periods, the canalicular structur e was well preserved. Na+K+ -ATPase and Mg2+ -ATPase activities in mem brane fractions enriched in bile canalicular complexes decreased signi ficantly at 15 min and remained low up to Day 5. Mg2+ -ATPase activity returned to control levels by Day 5. The lipid constituents of liver cell membranes enriched in canalicular complexes showed no significant variations 90 min after toxin treatment but, at 24 hr, phospholipid c ontent rose and membrane fluidity increased. These results clearly ind icate that the bile flow variation after a single low dose of phalloid in can be dissociated from specific pericanalicular microfilament dist ribution, lending further support to the view that normal biliary func tion is not strictly dependent on the integrity of the actin filament network. (C) 1996 Academic Press, Inc.