Culture conditions affect Ca2+ release in artificially activated mouse and human oocytes

Inconsistent fertilisation and pregnancy rates have been reported by different laboratories after application of ionomycin as a clinical method of assisted oocyte activation (AOA) to overcome fertilisation failure. Using both mouse and human oocytes, in the present study we investigated the effects of ionomycin and Ca2+ thorn concentrations on the pattern of Ca2+ thorn release and embryonic developmental potential. In the mouse, application of 5 mu M ionomycin in potassium simplex optimisation medium (KSOM) or 10 mu m Mionomyc in in Ca2+ thorn-free KSOM significantly reduced the Ca2+ thorn flux and resulted in failure of blastocyst formation compared with 10 mM ionomycin in KSOM. Increasing the Ca2+ thorn concentration up to three-or sixfold did not benefit mouse embryonic developmental potential. Similarly, 10 mM ionomycin-induced rise in Ca2+ thorn in human oocytes increased with increasing total calcium concentrations in the commercial medium. Remarkably, we observed significantly reduced mouse embryo development when performing AOA over a period of 10 min in Quinn's Advantage (TM) Fertilisation medium (Cooper Surgical) and IVF (TM) medium (Vitrolife) compared with Sydney IVF COOK cleavage medium (Cook Ireland), using the same sequential culture system from the post-activation stage to blastocyst formation stage in different AOA groups. In conclusion, concentrations of both ionomycin and Ca2+ thorn in culture media used during AOA can have significant effects on Ca2+ thorn release and further embryonic developmental potential.