TUBULOVESICULAR TRANSPORT OF HORSERADISH-PEROXIDASE IN ISOLATED RAT HEPATOCYTE COUPLETS - EFFECTS OF LOW-TEMPERATURE, CYTOCHALASIN-B AND BILE-ACIDS

The transcytotic vesicular pathway in isolated rat hepatocyte couplets was investigated using horseradish peroxidase. Ten to 20 min after ho rseradish peroxidase labeling, vesicles and tubules containing horsera dish peroxidase were observed to be predominantly around the bile cana liculi. In hepatocytes incubated in a 4 degrees C medium for 10 min af ter horseradish peroxidase labeling, few horseradish peroxidase-contai ning structures were observed around the bile canaliculi, and the fine reticular immunofluorescence of microtubules was reduced. Cells treat ed with cytochalasin B (a microfilament inhibitor) showed a fair numbe r of horseradish peroxidase containing structures around the markedly dilated bile canaliculi and the distribution of microtubules was prese rved. Cells labeled by horseradish peroxidase and then incubated for 1 0 min in a horseradish peroxidase-free medium containing 50 mu mol/L o f taurocholic acid, ursodeoxycholic acid or tauroursodeoxycholic acid had more tubular structures containing horseradish peroxidase around t he bile canaliculi than control cells, whereas 50 mu mol/L of tauroche nodeoxycholic acid, taurodeoxycholic acid, dehydrocholic acid and taur odehydrocholic acid each failed to increase the number of tubular stru ctures. These findings show that horseradish peroxidase was transporte d in hepatocyte couplets from the cell periphery to the bile canalicul ar front through the tubulovesicular pathway, depending on cytoplasmic microtubules. Cytoplasmic microfilaments appeared to play a minor rol e in this transport. Several specific bile acids such as taurocholic a cid, ursodeoxycholic acid and tauroursodeoxycholic acid each promoted the tubular transformation.