Helix pomatia lectin (HPL) bound to colloidal gold was used as a specific cytochemical probe for the localization of terminal nonreducing N-acetyl-D-galactosamine residues in thin sections of rat kidney. In the glomerulus, lectin-binding sites were associated only with the podocyte foot process bases and were not found on the free cell surface of podocytes or on any other glomerular components. Gold-particle label was often arranged in the form of clusters which extended from the foot process base to the lamina rare externa and lamina densa of the basement membrane. In contrast, wheat germ lectin (WGL)-binding sites (beta-[1 leads to 4] linked N-acetyl-D-glucosamine residues and N-acetylneuraminic acid residues) were found in all regions of the podocyte plasma membrane and on the cell surface of all other glomerular cell types. In addition, WGL-binding sites were present in all three layers of the glomerular basement membrane (GBM) as well as in the mesangial matrix. A quantitative evaluation of the pattern of labeling for HPL-binding sites together with the sugar specificity of this lectin suggest that a component of the glycocalyx is being detected rather than a basement membrane component. This was confirmed by the absence of H. pomatia lectin-binding sites in preparations of isolated GBM which retained, however, wheat germ lectin-binding sites. These data show that the glycocalyx of the foot process base is a highly specialized cell surface domain with respect to its carbohydrate composition.

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