Endocytosis and transcytosis of albumin gold through mice peritoneal mesothelium.

The present transmission electron microscopy (TEM) study was designed to investigate whether mesothelial cells of mice diaphragmatic, parietal and mesenteric peritoneum are actively coupled to the mechanisms involved in the transerosal absorption of albumin gold complexes (Alb-Au). Five albino mice were injected intraperitoneally with 0.5 ml of a suspension of Alb-Au. In three animals, in vivo fixation was done 10 minutes after injection of Alb-Au, whereas in the remaining two, fixation was performed 45 minutes after injection of the tracer. At both time intervals, a substantial part of Alb-Au complexes was observed within plasmalemmal and coated vesicles, mainly attached to the luminal aspect of the internal luminal membranes. The amount of Alb-Au contained in plasmalemmal vesicles was significantly higher than that detected in intermesothelial junctions. Plasmalemmal vesicles were observed discharging Alb-Au complexes in the submesothelial interstitium, showing a significantly higher proportion of the tracer associated with non-junctional areas. Evidence presented in this study supports the idea of local degradation of Alb-Au in mesothelial cells after endocytosis, and that of a continuously transcytotic mechanism transporting polymerized albumin across the mesothelial layer. In this sense, transcytotic vesicles could represent the large pore equivalent.