Freeze replica observations on the junction structures in the guinea-pig liver after bile duct ligation and recanalization.

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Abstract
The fine structures and distributions of the tight and gap junctions in guinea pig bile canalicules were examined by the freeze-fracture replica method. In order to correlate the structure and function of the cell junctions in the guinea pig hepatocytes were studied by EM after ligation for 6-96 h of the hepatic common duct and partly after recanalization. The junctional structures in a normal condition were characterized by fine configurations of fully formed tight junctional networks and gap junctions. Duct ligation caused: reduction in number of the tight junctional strands, enlargement of the tight junctional compartments and sudden appearance of gap junctions near the tight junction network; the disruption of the tight junctional strands into small clusters; abluminal stretching of focal strands, often continuous with the gap junctions; sudden disappearance of the gap junctions late after ligation; particle aggregates surrounded by or integrated in the tight junctional strands, which were considered as reserve aggregates and extremely disordered tight junction networks without any gap junctions, indicating a leaky pattern. Recanalization was followed by prompt reassembly of tight junctions with abundant desmosomes and delayed appearance of gap junctions. Jaundice may occur in the following way: soon after the duct ligation, bile may leak through the disrupted tight junction networks and dilatations of the intercellular space may affect the dissociation of the gap junctions; such regurgitation of the bile through the space of Disse may cause bilirubinemia. The reconstitution of the junctional complexes may occur in the following way: soon after the release from the obstruction, the reserve aggregates of intramembraneous particles may be scattered to repair the disrupted tight junction networks lacking in diverse gap junctions and, with the later appearance of gap junctions, the junctional complexes are completely repaired. These morphological features coincide with the results of biochemical examination of the serum bilirubin levels of the guinea pigs.