A molecular model of basement membrane structure and function

Basement membranes, and specifically, their highly sulfated proteoglycans, generate a size and charge selective filtration system that functions to regulate the passage of serum proteins into the urine. In this report, a model is presented that demonstrates the importance of the electrostatic repulsive force generated by the anionic proteoglycans in creating a charge selective barrier with dimensions appropriate for the reported molecular size filtration capabilities of the glomerular basement membrane. However, what prevents the neutralization of the anionic proteoglycans? Using pulsed proton nuclear magnetic resonance titration, it was found that tissues enriched in proteoglycans were also highly enriched in very tightly bound water of hydration. The water of hydration of the proteoglycans is so tightly bound in the first monolayer that it prevents counterions from neutralizing the anionic charge on the proteoglycan, yet allows the electrostatic repulsive force (5-10 nm thick) to exert its influence on filtration.