Subcellular localization of calcium and Ca-ATPase activity during nuclear maturation inBufo arenarumoocytes

Abstract

The localization of calcium and Ca-ATPase activity in Bufo arenarum oocytes was investigated by ultracytochemical techniques during progesterone-induced nuclear maturation, under in vitro conditions. No Ca2+ deposits were detected in either control oocytes or progesterone-treated ones for 1-2 h. At the time when nuclear migration started, electron dense deposits of Ca2+ were visible in vesicles, endoplasmic reticulum cisternae and in the space between the annulate lamellae membranes. Furthermore, Ca-ATPase activity was also detected in these membrane structures. As maturation progressed, the cation deposits were observed in the cytomembrane structures, which underwent an important reorganization and redistribution. Thus, they moved from the subcortex and became located predominantly in the oocyte cortex area when nuclear maturation ended. Ca2+ stores were observed in vesicles surrounding or between the cortical granules, which are aligned close to the plasma membrane. The positive Ca-ATPase reaction in these membrane structures could indicate that the calcium deposit is an ATP-dependent process. Our results suggest that during oocyte maturation calcium would be stored in membrane structures where it remains available for release at the time of fertilization. Data obtained under our experimental conditions indicate that calcium from the extracellular medium would be important for the oocyte maturation process.

Advances in Oocyte Maturation In Vivo and In Vitro in Mammals

“…Increased cytoplasmic Ca 2+ levels can also trigger the activity of calcium/calmodulin-dependent protein kinase II (CaMK II), which influences oocyte maturation. In addition, Ca 2+ release can mediate the meiosis process in conjunction with ATP [66].…”

Phosphoinositide and phospholipid phosphorylation and hydrolysis pathways<br/>—Organophosphate and organochlorine pesticides effects<br>

“…Ramos et al [53] demonstrated the presence of intracellular calcium storages, as well as their localization and their migration during Bufo arenarum oocytes maturation. They also observed that these storages were located near the cortical region in mature oocytes and that they were ready for release during fertilization.…”