Immunoreactivity of sensory hair bundles of the guinea-pig cochlea to antibodies against elastin and keratan sulphate

The stereociliary bundles of hair cells contain cross-linking extracellular filaments which have been suggested to play a role in mechanoelectrical transduction. To investigate the composition of these filaments, antibodies to the extracellular matrix molecules elastin and keratan sulphate have been used for light- and electron-microscopic immunocytochemistry of the guinea-pig organ of Corti. With the antibody to elastin, no immunoreactivity was found in hair bundles. This implies either that the epitope recognised by this antibody is not present in the links or that it is obscured. The antibody to keratan sulphate labelled the stereociliary bundles of both inner and outer hair cells but not supporting cells. The tips of the tallest stereocilia, especially on outer hair cells, the tips of the shorter stereocilia where the tip links attach to the stereociliary membrane, and the attachments of the lateral links, were labelled. This suggests that the links contain keratan sulphate proteoglycans, molecules which in other tissues are known to maintain structural integrity and fibrillar spacing, and to influence the microenvironment of the cell surface.