The distribution of anionic groups of acid mucopolysaccharides on the surface of glomerular constituents of a brwon hagfish, Paramyxine atami Dean, has been studied morphologically. The ionized anionic groups of acid mucopolysaccharides were labeled on fixed tissues by stainig with cationic cacodylate iron colloid (Fe-Cac) at pH 4.0. The glomerular permeability to cationic and anionic macromolecules was observed morphologically in the kidney of the animal injected native anionic ferritin (NF) or cationized ferritin (CF) into the dorsal aorta.
Histochemical staining of tissues with Fe-Cac (pH 4.0) revealed the ionized anionic groups of acid mucopolysaccharides on both luminal and abluminal surfaces of endothelial cells, within the glomerular basement membrane (GBM), and on the visceral epithelial cell surface facing the urinary space. The CF molecules introduced into the dorsal aorta easily passed through the fenestrae of the capillary endothelial cell layer and the thick fibrillar GBM, reaching the urinary space to be adsorbed to the visceral epithelial cell surface or taken up by these visceral epithelial cell. On the other hand, NF hardly passed through the capillary wall. These results show that the nonosmoregulating mesonephric glomerulus of the brown hagfish has a working anionic barrier system. The function of its glomerulus is compared to that of the mammalian metanephric glomerulus.