In vitro calcium ion turnover in otoconia of the guinea pig

In vitro calcium ion turnover into otoconia of adult guinea pigs was investigated by the use of tetracycline. The incubation in tetracycline in vitro clearly demonstrated the deposition of tetracycline (fluorescence) on the outer surface of otoconia. Levels of Ca2+ uptake in utricular otoconia were higher than those in saccular otoconia. In vitro uptake and/or exchange of Ca2+ was greater in fluid with a high K+/Na+ ratio than in fluid in which the ratio was low. It has been thus indicated that a high K+/Na+ ratio in normal endolymph should be more suitable for Ca2+ uptake and/or exchange to maintain the ionic environment in the inner ear. Sodium dodecyl sulfate treatment of otoconia increased the Ca2+ uptake. The ability of the otoconia to take up Ca2+ appears to decline with age. It has been indicated that the organic matrix of otoconia may be one of the inhibitory factors for Ca2+ uptake in old animals