Disruption of cortical granules and microvilli by the brief exposure to ionomycin leads to depletion of the ionomycin-sensitive Ca²⁺ stores.

A. aranciacus oocytes at the GV stage were exposed to 5 µM ionomycin for 3 min before switched to the media containing 1-MA. (A) After 1 h incubation, the mature eggs were fixed with glutaraldehyde and analyzed by TEM. Blue arrows indicate the remnant of the cortical granules that were extruded in the perivitelline space. Red arrows indicate fragments of cortical granules being engulfed by white vesicles. Scale bar = 10 µm. (B) The same batch of oocytes were exposed to 5 µM ionomycin for 3 min and switched to the fresh media containing 1-MA. After GV breakdown, the mature eggs were microinjected with Calcium Green/Rhodamine Red and subsequently re-exposed to 5 µM ionomycin (t = 0) to monitor the Ca²⁺ response. The trajectory of intracellular Ca²⁺ levels in the eggs with or without (control) ionomycin pretreatment were depicted in brown and green curves, respectively.