Polyanionic constituents of the glomerular capillary wall have been previously shown to have a primary role in the control of glomerular filtration. In the study presented here, the distribution and biochemical nature of polyanionic constituents in proximal (PT) and distal (DT) tubules have been investigated as possible determinants of tubulointerstitial function. For histochemical localization of sialic acid, paraffin sections were treated with Arachis hypogaea lectin (PNA) before and after neuraminidase treatment. Electron microscopic characterization of glycosaminoglycans (GAG) was performed on thin LR-white sections, using cationic colloidal gold (CCG) as an histochemical probe, and GAG-degrading enzymes. Without neuraminidase, PNA binded to collecting ducts but not to PT or DT. Neuraminidase pretreatment resulted in intense PNA binding to the tubulointerstitial blood vessels but only in mild apical tubular binding, which implies a lack of sialoglycoconjugates in the tubular basolateral membranes. In contrast, all PT and DT showed intense CCG binding to basolateral, but not to apical, membranes. All basement membranes showed CCG labeling, with considerable variations in labeling densities between PT (124 +/- 8.8/micron 2) and DT (52 +/- 1.8/micron 2), as well as between tubules and Bowman's capsule (P < 0.0001). Heparinase III treatment induced an almost complete loss of CCG binding in all basement and basolateral membranes, whereas chondroitinase ABC treatment led to a lesser but significant loss (P < 0.0001). The results indicate that rat tubulointerstitium expresses polyanionic constituents, consisting mainly of heparan and chondroitin sulfate. The role of these anionic sites in tubular function has yet to be clarified.