ULTRASTRUCTURE OF THE INTRACELLULAR MEMBRANOUS SYSTEM OF RAT HEPATOCYTES IN INTRAHEPATIC CHOLESTASIS INDUCED BY PHALLOIDIN

To investigate the effect of a thickened pericanalicular ectoplasm in tubulovesicular transport and biliary excretion, we examined the ultra structure of the intracellular membranous system in rat hepatocytes wi th and without phalloidin treatment, by transmission electron microsco py and scanning electron microscopy combined with the Aldehyde prefix Osmium-Dimethyl Sulfoxide-Osmium method. Hepatocytes possessed elabora te networks of tubules around bile canaliculi, and some of them extend ed to the bile canaliculi in control rats. Vesicles were also present around the bile canaliculus. Treatment of rats with phalloidin produce d a thick pericanalicular ectoplasm around the bile canaliculus visual ized by transmission electron microscopy, and the density of vesicles (p<0.001) and tubules (p<0.001) within 0.5 mu m around the bile canali culus significantly decreased in phalloidin-treated rats. The number o f lysosomes in hepatocytes apparently increased in phalloidin-treated rats; however, they were rarely observed around the bile canaliculus. The Aldehyde prefix Osmium-Dimethyl Sulfoxide-Osmium method produced a n organelle-free space around the bile canaliculus by removing the thi ck pericanalicular ectoplasm in scanning electron microscopic examinat ion, and the thickened pericanalicular ectoplasm inhibited the approac h of intracellular membranes to the canalicular membrane in the transm ission electron microscopic examination. In some pathological cholesta tic conditions, the thickened pericanalicular ectoplasm may inhibit no t only bile canalicular contraction but also biliary excretion of subs tances, which is mediated by the tubulovesicular transport system. (C) Journal of Hepatology.