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Effects of cytochalasin D and colchicine on the uptake, translocation, and biliary secretion of horseradish peroxidase and [14C]sodium taurocholate in the rat.

The roles of microfilaments and microtubules in the hepatocellular uptake, translocation, and biliary excretion of horseradish peroxidase and [14C]sodium taurocholate were investigated using the microfilament inhibitor cytochalasin D and the microtubule inhibitor colchicine. In separate studies, horseradish peroxidase and [14C]taurocholate were injected separately as a bolus into rat portal veins after treatment with cytochalasin D or colchicine, and bile was collected and analyzed for the presence of horseradish peroxidase and [14C]taurocholate. Cytochalasin D treatment depressed bile flow by approximately 50% and decreased the biliary secretion of [14C]taurocholate in direct proportion to bile flow. Horseradish peroxidase secretion into bile was unaffected, and total biliary protein secretion was decreased only slightly. Because of the depression of bile secretion, concentrations in bile of horseradish peroxidase and total biliary protein increased significantly. Consistent with reported observations of cytochalasin D, decreases in microfilaments and dilated bile canaliculi were observed by electron microscopy; however, the vesicular transport of horseradish peroxidase as observed using electron microscopy cytochemistry appeared to be normal and unaffected by cytochalasin D treatment. Colchicine, in contrast, had minimal effect on bile flow and did not diminish the biliary secretion of [14C]taurocholate. Colchicine inhibited both the total amount of horseradish peroxidase secreted into bile as well as the rate of its secretion in comparison with control and cytochalasin D-treated animals. Cellular morphology was consistent with published observations for colchicine, which included a marked decrease in microtubules. In addition, after electron microscopy cytochemistry there was a paucity of horseradish peroxidase-containing vesicles within the hepatocytes, suggesting that colchicine interfered with the vesicular transport of horseradish peroxidase. Collectively, the data suggest that (a) the mechanism used by hepatocytes for the secretion of bile acids is independent of the vesicular transport of biliary proteins and is dependent upon intact microfilaments and (b) such vesicular transport of protein into bile requires an intact and functioning microtubular network.