DISTRIBUTION OF GLYCOSAMINOGLYCANS IN RAT RENAL TUBULAR EPITHELIUM

Polyanionic constituents of the glomerular capillary wall have been pr eviously shown to have a primary role in the control of glomerular fil tration. In the study presented here, the distribution and biochemical nature of polyanionic constituents in proximal (PT) and distal (DT) t ubules have been investigated as possible determinants of tubulointers titial function. For histochemical localization of sialic acid, paraff in 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, u sing cationic colloidal gold (CCG) as an histochemical probe, and GAG- degrading enzymes. Without neuraminidase, PNA binded to collecting duc ts 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 i n 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/mu m(2)) and DT (52 +/- 1.8/mu m(2), as well as between tubules and Bowman's capsule (P < 0.00 01). Heparinase III treatment induced an almost complete loss of CCG b inding in all basement and basolateral membranes, whereas chondroitina se ABC treatment led to a lesser but significant loss (P < 0.0001). Th e results indicate that rat tubulointerstitium expresses polyanionic c onstituents, consisting mainly of heparan and chondroitin sulfate. The role of these anionic sites in tubular function has yet to be clarifi ed.