Subcellular Localization of Ca-ATPase and Calcium in Bufo arenarum Oviducts

The localization of calcium and Ca−ATPase activity in Bufo arenarum oviducts was investigated by ultrahistochemical techniques during the sexual cycle. In the preovulatory period prominent calcium deposits were detected in the secretory granules of epithelial and glandular cells as well as in close proximity to the plasma membranes. Furthermore, intense Ca−ATPase activity was found outlining the plasma and secretory granule membranes. Regional differences along the oviduct were observed. Immediately after ovulation the above−mentioned cells exhibited a marked reduction of calcium deposits and Ca−ATPase activity, but during hibernation this situation progressively reverted. These results demonstrate that the most prominent calcium deposits can be detected in the cellular structures that, through different secretion mechanisms, release their products towards the oviductal lumen to form the structural network of the jelly coats. The variations in calcium contents in the oviduct and the animal cycle changes in serum calcium levels are closely related with the fluctuations of estradiol serum levels during the sexual cycle, suggesting hormonal regulation.