Formation and calcium incorporation of giant otoconia of the guinea pig after streptomycin intoxication

Abstract

The mechanisms for the formation and fate of giant otoconia following streptomycin (SM) intoxication were investigated in adult pigmented guinea pigs by scanning electron microscopy. Calcium turnover into otoconia has also been studied by using tetracycline as a tracer. The administration of SM induced the reduction of otoconia with the formation of giant otoconia. The giant otoconia had a multifaceted morphology in their early developmental period. This type of otoconia showed entire fluorescence indicating existence of calcium uptake. They then grew up to the transitional type and finally to the cylindrical type. The giant otoconia were thought to be formed mainly by dissolution of normal otoconia due to the loss of environmental calcium followed by recrystallization as giant crystals. The transitional type of giant otoconia showed less calcium ion uptake and the removal of calcium from the giant otoconia caused their quick disappearance. These phenomena might be closely related to the otoconial dynamics which may regulate calcium ion homeostasis of endolymph.