Immunogold localization of procollagen III, fibronectin and heparan sulfate proteoglycan on ultrathin frozen sections of the normal rat liver.

In the present study, we have localized by immunocytochemistry at the LM and EM level, procollagen type III (PIIIP), fibronectin (FN) and heparan sulfate proteoglycan (HSPG). Intracellularly, PIIIP was observed in both parenchymal and endothelial cells. In parenchymal cells, PIIIP was found in Golgi derived vesicles. This observation suggests that PIIIP synthesis is a normal function of liver parenchymal cells. In endothelial cells, vesicles, which could not be identified, were seen to contain PIIIP. This result does not allow to conclude, whether sinusoidal endothelial cells secrete or take up PIIIP. Extracellularly, PIIIP was present around portal and central veins, in the space of Disse and between adjacent parenchymal cells. In the space of Disse, almost all interstitial collagen fibrils reacted with the anti PIIIP antibodies. This observation leads to the conclusion that most fibrils of the space of Disse contain type III in addition to type I collagen molecules. By immunofluorescence, FN was seen mainly along the sinusoids in discrete dots. By EM, FN was found to be present in diffuse material closely associated with the sinusoidal membrane of the parenchymal cells and in strands connecting adjacent parenchymal cells, parenchymal and endothelial cells or parenchymal cells and collagen fibrils. FN was also present in vascular and ductular basal laminae. Strong HSPG reaction was observed around bile ducts. Moderate reaction was seen around blood vessels and in the space of Disse. In the latter location, the ultrastructural distribution of HSPG resembles that of FN, i.e. HSPG is present in diffuse material and in strands.