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Abstract

Using immunohistochemical techniques, the distribution of the "classic" S100 calcium binding proteins, α (A1) and β (B), was determined in the mammalian vestibular end organs. An affinity-purified polyclonal antibody which recognized both the A1 and B subunits and two monoclonal antibodies specific for either the A1 or the B subunit were used in this study. S100A1 was localized specifically to the basal region of the sensory epithelium (saccular macula, cristae ampullaris and utricular macula) when a cross-linking fixative (4% paraformaldehyde) was utilized. Using a fixation protocol including paraformaldehyde and a precipitating fixative revealed an additional localization of S100A1 to the apical region of the saccular macula, cristae ampullaris and utricular macula. This indicates the presence of two populations of S100A1 in these cells: a cytosolic (soluble) component; and a membrane-bound fraction. In contrast, S100B was localized to the layer of the vestibular nerve fibers. Immunoreactivity for S100B was not observed in the sensory epithelium of the saccular or utricular macula or in the cristae ampullaris. The preferential distribution of S100B to the nerve fibers and S100A1 to cells of the sensory epithelium, in two forms (cytosolic and membranebound), may be important in the functional roles of S100 proteins in the vestibular sensory end organs.