Localization of pyroantimonate-precipitable calcium in the vestibular organs of the rat and guinea pig.

Localization of pyroantimonate-precipitable calcium (Ca) was examined in the vestibular organs of the rat and the guinea pig. Precipitates were observed around the otoconia and in the otolithic membranes of the macula sacculi and macula utriculi. Although the deposition was heavier in the rat than in the guinea pig, the distribution of the Ca-pyroantimonate was similar in both species. Most otoconia in the dark cell area had precipitates around and inside the otoconia. Furthermore, there was some precipitation in the cupulae of the semicircular canals in both animals. The presence of Ca in the precipitates was confirmed by X-ray microanalysis and extraction with EGTA. Localization of the Ca-pyroantimonate around the otoconia in these animals agrees with localization of precipitates of endolymphatic crystals in the tree frog, which are known to grow mainly by accretion. Thus, the otoconia of the rat, and probably also of the guinea pig, can be assumed to grow mainly by accretion.