EFFECTS OF CHOLESTATIC AGENTS ON THE STRUCTURE AND FUNCTION OF BILE CANALICULI IN NEONATAL RAT HEPATOCYTES IN PRIMARY CULTURE

The effects of cytochalasin B and colchicine on the structure and func tion of bile canaliculi were studied in neonatal rat hepatocytes in pr imary culture. Cellular contacts of neonatal hepatocytes were not as t ight as those of adult hepatocytes. There was no remarkable difference in the ultrastructure of bile canaliculi between neonatal and adult h epatocytes. Neonatal hepatocytes treated with cytochalasin B were roun d in shape and aggregated in groups of several cells. Actin filaments stained by rhodamine-phalloidin were disrupted and condensed at the ce ll periphery or around dilated bile canaliculi. Markedly-dilated bile canaliculi with less microvilli were observed by transmission electron microscopy while the secretory function of horseradish peroxidase, wh ich was used as a marker for uptake, transport and secretion into bile canaliculi, were maintained. The lumen of dilated bile canaliculi was found close to the undersurfaces of hepatocytes by scanning electron microscopy after turning over the cultured cells. By colchicine treatm ent, the filamentous structure of microtubules in neonatal hepatocytes disappeared. The ultrastructure of the bile canaliculi was not affect ed by the treatment, but transport and secretion of horseradish peroxi dase into bile canaliculi were inhibited. The development of strict ce llular polarity in neonatal hepatocytes may be suppressed in neonatal hepatocytes; however, cholestatic agents which rearrange the cytoskele ton caused the same morphological or functional changes of bile canali culi as in adult hepatocytes.