An insufficient increase of cytosolic free calcium level results postovulatory aging-induced abortive spontaneous egg activation in rat

The present study was aimed to find out whether postovulatory aging-induced abortive spontaneous egg activation (SEA) is due to insufficient increase of cytosolic free Ca2+ level. Immature female rats (22-24 days old) were subjected to superovulation induction protocol. Eggs were collected 14, 17 and 19 h post-hCG surge to induce in vivo egg aging. The eggs were collected 14 h post-hCG surge and cultured in vitro for 3, 5 and 7 h to induce in vitro egg aging. The morphological changes, rate of abortive SEA, chromosomal status and cytosolic free Ca2+ levels were analyzed. Postovulatory aging induced morphological features characteristics of abortive SEA in a time-dependent manner in vivo as well as in vitro. The extracellular Ca2+ increased rate of abortive SEA during initial period of culture, while co-addition of a nifedipine (L-type Ca2+ channel blocker) protected against postovulatory aging-induced abortive SEA. However, CI induced morphological features characteristics of egg activation (EA) in a dose-dependent manner. As compare to control, an increase of cytosolic free Ca2+ level (1.42 times) induced abortive SEA, while further increase of cytosolic free Ca2+ level (2.55 times) induced EA. Our results show that an insufficient cytosolic free Ca2+ level is associated with postovulatory aging -induced abortive SEA, while furthermore increase is required to induce EA in rat.