Effect of two assisted oocyte activation protocols used to overcome fertilization failure on the activation potential and calcium releasing pattern

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To assess the effect of two assisted oocyte activation (AOA) protocols with the use of two calcium (Ca(2+)) ionophores, ionomycin and A23187 (calcimycin), on the intracellular Ca(2+) level in mouse and human oocytes and the fertilization rates. Comparison of two Ca(2+) ionophores, ionomycin and A23187, regarding their capacity to increase the intracellular Ca(2+) level and to support subsequent oocyte activation and development. University hospital research laboratory. Patients undergoing intracytoplasmic sperm injection (ICSI) treatment and B6D2F1 mice. Assisted oocyte activation and microinjection of mouse and human oocytes with sperm. Measurement of the fertilizing and Ca(2+)-releasing ability of human sperm. Ionomycin was more potent than A23187 in provoking Ca(2+) increases in both mouse and human oocytes with significantly higher amplitude and area under the receiver operating characteristic curve. The oocyte activation rate was significantly higher when mouse oocytes were activated with the use of the ionomycin- rather than the A23187-based AOA protocol. Furthermore, oocyte activation rate was higher when human in vitro matured oocytes were activated with the ionomycin-based AOA protocol, but the difference did not reach statistical significance. In both mouse and human oocytes, the AOA protocol that used ionomycin was more efficient than the one that used A23187. Bearing in mind that mammalian fertilization is successful when the total dose of Ca(2+) released reaches a minimal threshold, the use of ionomycin for human AOA might be justified instead of the use of A23187.