Characterization of basement membranes of rat choroid plexus using the critical electrolyte concentration technique.

Using the critical electrolyte concentration technique, with ruthenium red as a strain for polyanionic macromolecules, we examined the basement membranes of the rat choroid plexus. Concentrations of Na+ exceeding 3.0 M were required to reversibly inhibit discrete staining of endothelial and epithelial basement membranes by ruthenium red, whereas 2.5 M Na+ inhibited staining of renal pertitubular capillary basement membranes. The findings are consistent with recent evidence that basement membranes underlying fenestrated capillaries are more polyanionic that those underlying continuous capillaries, and suggest that basement membranes of the choroid plexus are more polyanionic than those of peritubular capillaries.