The process of otoconia formation in guinea pig utricular supporting cells

In order to clarify the mechanism of otoconia formation, the pathway of calcium transport in the utricular supporting cells was investigated. Potassium pyroantimonate (PA) precipitation, which indicates the localization of calcium ions, was seen not only in otoconia but also in supporting cell cytoplasm. In the latter, deposits of PA were detected in the secretory granules and endoplasmic reticulum (ER). These deposits were not present in cells pretreated with ethylene glycol-O,O,-bis (2-aminoethyl)-N,N,N',N'-tetra-acetic acid (EGTA). Exposure of the supporting cells to streptomycin sulfate (SM) increased the number of lysosomes. These lysosomes contained many small deposits of PA. The remaining granules and ER in cytoplasm also contained small deposits of PA. The findings suggest that otoconia are formed by the vestibular supporting cells in which calcium ions might be transported via ER-secretory granule-lysosome-cytoplasmic protrusion.