A change barrier has been found for the first time in the glomerular basement membrane of the kindey and plays an important role in the filtration of solutes. In the guinea pig cochlea, Tomoda et al have reported the similar structures located in the strial capillary basement membrane. In the present study, we observed electronmicroscopically the anionic sites of the charge barrier in the healthy guinea pig endolymphatic sac. The tissues removed after the decapitation were immersed in the solution of cationized polyethyleneimine (PEI, MW 1800). The results showed an arrangement of PEI with two strata in the basement membrane of the epithelium and the capillary. These sites function as a charge barrier, and their locations in the endoymphatic sac may play important roles in the filtration system of water, ion and macromolecules.
