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 ultrastructure of the intracellular membranous system in rat hepatocytes with and without phalloidin treatment, by transmission electron microscopy and scanning electron microscopy combined with the Aldehyde prefix Osmium-Dimethyl Sulfoxide-Osmium method. Hepatocytes possessed elaborate networks of tubules around bile canaliculi, and some of them extended to the bile canaliculi in control rats. Vesicles were also present around the bile canaliculus. Treatment of rats with phalloidin produced a thick pericanalicular ectoplasm around the bile canaliculus visualized by transmission electron microscopy, and the density of vesicles (p < 0.001) and tubules (p < 0.001) within 0.5 microns around the bile canaliculus significantly decreased in phalloidin-treated rats. The number of 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 an organelle-free space around the bile canaliculus by removing the thick pericanalicular ectoplasm in scanning electron microscopic examination, and the thickened pericanalicular ectoplasm inhibited the approach of intracellular membranes to the canalicular membrane in the transmission electron microscopic examination. In some pathological cholestatic conditions, the thickened pericanalicular ectoplasm may inhibit not only bile canalicular contraction but also biliary excretion of substances, which is mediated by the tubulovesicular transport system.