Immunohistochemical localization of keratan sulfate and chondroitin 4- and 6- sulfate proteoglycans in subregions of the tectorial and basilar membranes

Proteoglycans containing keratan sulfate (KSPG) and 4- and 6-sulfated epitopes of chondroitin sulfate (CSPG) were identified in distinct domains of the tectorial and basilar membranes by ultrastructural immunogold labeling with monoclonal antibodies. In the tectorial membrane (TM), the highest concentration of gold particles was present in the upper fibrous layers of the limbal, middle and marginal zones with all three antibodies. Reactivity with anti-KSPG exceeded that with anti-4S and anti-6S CSPG, especially in the marginal zone. The cover net showed no reactivity for any antibody. Labeling density of gold particles with all three antibodies increased markedly from base to apex. In the basilar membrane (BM), all three PGs were most highly concentrated in regions of amorphous ground substance bordering the upper and lower filamentous bands. As in the TM, reactivity for anti-KSPG in the BM exceeded that for either CSPG antibody and staining with all three antibodies was stronger and more widespread in the apical as compared to the basal turns. These results provide the first ultrastructural demonstration of KSPG and CSPG in distinct subregions of the TM and BM. The preferential distribution and marked increase in PGs from base to apex in both TM and BM supports a role for these macromolecules in regulating structural and mechanical properties of these highly specialized extracellular membranes.