Immunohistochemical identification of proteoglycans in gelatinous membranes of cat and gerbil inner ear

Proteoglycans have been identified in gelatinous membranes of adult cat and gerbil inner ears using highly specific histochemical techniques. The tectorial and otoconial membranes and cupula of both species stained strongly with high iron diamine which is specific for sulfate esters and with monoclonal antibody against keratan sulfate proteoglycan (KSPG). The cat tectorial membrane also showed strong immunoreactivity with monoclonal antibody against chondroitin sulfate proteoglycan (CSPG) but the gerbil tectorial membrane reacted only weakly with this antibody. Otoconial membranes and the cupula of both species showed little if any immunostaining with antibodies against CSPG. Supporting cells in the vestibular neurosensory epithelium and planum semilunatum cells in the ampullae of the cat stained strongly with anti-KSPG, demonstrating the origin of KSPG in the cat. These cell types failed to stain in the gerbil, however, suggesting a different mechanism of secretion or a slower rate of turnover of membraneous KSPG in the gerbil. Interdental cells of both species failed to react with either antibody, leaving the origin of tectorial membrane proteoglycans in question. The approach used here provides a highly sensitive and reliable means of assessing the contribution of specific proteoglycans to inner ear structure and function.