3-DIMENSIONAL ORGANIZATION OF RAT HEPATOCYTE CYTOSKELETON - RELATION TO THE ASIALOGLYCOPROTEIN ENDOCYTOSIS PATHWAY

Analysis by confocal microscopy has revealed features of the microtubu le network of rat hepatocytes in culture, establishing the three-dimen sional disposition of the microtubule-based cytoskeleton, its relation to the actin-based cytoskeleton and to ligand-containing endosomes du ring receptor-mediated endocytosis and the alterations in its structur e and disposition by the microtubule pertubant, Taxol, By co-localizat ion studies, we have been able to demonstrate that the microtubules ha ve a significant role in receptor-mediated endocytosis of asialoglycop roteins in this cell. Asialoorosomucoid-containing endosomes attach to widely spaced arrays of microtubules running under the base-lateral s urface of the hepatocytes 5-15 minutes after the initiation of endocyt osis and then travel along microtubule paths to become concentrated wi th microtubules near the centrosome and at bile canaliculi after 30-60 minutes of receptor-mediated endocytosis, Receptor-mediated endocytos is is affected, but not abolished by Taxol, which inhibits the rate of asialoorosomucoid degradation at the same concentrations as those tha t disrupt microtubule and cytoplasmic dynein distribution, and that pr event the concentration of endosomes centrally, The results support su ggestions that asialoorosomucoid-containing endosomes are captured by microtubules just below the actin layer at the cell periphery and thes e are actively transported centrally along micro-tubules, possibly by cytoplasmic dynein, so that the concentration of endosomes near the ce ntrosome, and the subsequent efficient lysosomal degradation of ligand , are consequences of the confluence of microtubules in this region.