Anionic sites in blood capillaries of the mouse cochlear duct

The blood-cochlear barrier, which consists of the molecular size and ionic charge barriers, is known to play an important role in production and absorption of inner ear fluids. In this study, we employed poly-L-lysine colloidal gold conjugates (PL-CG) in combination with Lowicryl K4M resin to demonstrate anionic sites in blood capillaries of the cochlear duct. Male ICR mice weighing 30-40 g with a positive Preyer's reflex were used. The basement membranes of blood capillaries of the stria vascularis and the spiral ligament were successfully labeled with PL-CG pH 2.5. The luminal surface of capillaries in the stria vascularis and the spiral ligament intensely reacted with PL-CG pH 2.5. However, PL-CG pH 1.0 stained only the basement membrane of the spiral ligament. Predigestion with several glycosidases nearly eliminated PL-CG labeling. Anionic charge located on the luminal surface of the endothelial cell was mainly caused by the presence of sialic acid. On the contrary, anionic charge of the basement membrane was caused in a substantial degree by chondroitin and heparan sulfate-rich glycosaminoglycans. We obtained histochemical evidence that blood capillaries of the stria vascularis differ from those of the spiral ligament.