STUDY OF GLOMERULAR PERMSELECTIVITY FOR PROTEINS OF THE GLOMERULAR-BASEMENT-MEMBRANE USING A DIALYZER MODEL

The glomerular basement membrane (GBM) is considered to regulate glome rular permselectivity for proteins by acting as both size barrier and charge barrier. Since heparan sulfate-proteoglycan (HS-PG), which form s the charge barrier of GBM, contains a sulfonic acid, we made membran es with various degrees of negative charge models of GBM by addition o f sulfonic acid to ethylene vinyl alcohol (EVAL) membranes. A high-res olution scanning electron-microscopic study revealed no ultrastructura l alterations after adding sulfonic acid to EVAL membranes. Both neutr ally and negatively charged membranes had porous structures in the inn er surface of the membranes. The interrelation between the two actions of size and charge of GBM was studied using special dialyzers with va rious degrees of negative charge and different pore sizes. The negativ ely charged membranes adsorbed proteins with positive charge and repul sed proteins with negative charge. The degrees of adsorption and repul sion were weaker in membranes with larger pores and were stronger for proteins with larger molecular weights. The permselectivity for protei ns of a charged membrane depends largely upon the interrelation betwee n the pore size of the membrane and the size of the proteins. It is, t herefore, suggested that the presence of a size barrier in GBM is nece ssary for the charge barrier to effectively exert glomerular permselec tivity for proteins. Our study may lead to the development of a dialyz er with higher permselectivity by adding sulfonic acid rather than con ventional dialyzers.