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The morphologic characteristics of intercellular junctions between normal human liver cells and cells from patients
Abstract:
In freeze-fracture replicas the bile canaliculi of normal human livers showed a lumen of rather constant size with parallel margins. The zonula occludens consists of a complex anastomosing network of intramembranous ridges on the P face and complementary grooves of the E face of the plasmalemma of liver parenchymal cells. The zonula occludens is usually composed of three to five ridges running parallel to the lumen of the bile canaliculus that are surrounded by a looser meshwork of variable orientation. All tight junctions observed in control replicas appeared as continuous barriers without any disruptions. Extrahepatic cholestasis produced considerable morphologic alterations in the canaliculi and tight junctions. The lumen of the canliculi enlarged, and the microvilli disappeared. Side branches, irregularities, and outpouchings of the canalicular membrane extending into the cytoplasm of the hepatocytes were frequently observed. The complexity of the branching pattern and the number of strands in the zonulae occludentes changed extensively. Junctional strands away from their usual pericanalicular location were present on the lateral surface of the plasma membrane. The altered zonulae occludents contain regions in which the strands had a fragmented appearance or were completely absent. These discontinuities in the junctional meshwork provide a direct pathway between the lumen of the bile canaliculus and the intercellular space. They strongly suggest a leakage of the canaliculosinusoidal barrier. Of further interest is the diffuse aggregation of the usually randomly distributed intramembranous particles of the P face of the plasmalemma. The aggregates consist of 10-50 individual particles. Concomitantly, the desmosomes appeared to be more numerous than normally. The number and structure of gap junctions remained unaffected. The results of this investigation are discussed in relation to those obtained after experimental bile duct ligation in rats.