Fine structural changes in the endolymphatic sac induced by calcium loading in the tree frog, Hyla arborea japonica.

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Abstract
The growth rate of calcium carbonate (CaCO3) crystals in the endolymphatic sac was modulated, and morphological changes in this organ were observed by light and electron microscopy. When calcium chloride (CaCl2) was given to the tree frog for a short period (3 days to 2 weeks), CaCO3 crystal production was acclerated. Epithelial cells enlarged, their rough endoplasmic reticulum (rER) and Golgi apparatus developed, and dense material increased around CaCO3 crystals and/or in the endolymphatic lumen. In addition, multiluminal endolymphatic chambers appeared in some frogs. On the other hand, as the CaCl2 loading period lengthened and CaCO3 crystal formation decreased or stopped, the epithelial cells became flat and extended with scanty cytoplasm, and the rER and Golgi apparatus decreased in number and size. Furthermore, the amount of dense material around CaCO3 cyrstals and in the lumen decreased. These findings suggest that the rER, Golgi apparatus and dense material have key roles in the production of CaCO3 crystals.