Activation of in vitro matured pig oocytes using activators of inositol triphosphate or ryanodine receptors

In our study, we observed the activation of in vitro matured pig oocytes and their subsequent parthenogenetic cleavage after stimulation of ryanodine receptors (RyR) using ryanodine (Ry), caffeine or cyclic adenosine diphosphate ribose (cADPri) or after stimulation of inositol triphosphate receptors (IP3R) using d-myo-inositol 1,4,5-triphosphate (IP3). Heparin, a potent blocker of IP3R, prevented the activation of porcine oocytes using IP3, but blockers of RyR (ruthenium red or procaine) prevented activation after stimulation by RyR and stimulation by IP3R using IP3. The drugs were injected into oocytes matured to the stage of metaphase II and activation was determined by assessment of pronuclear formation. The activity of H1 kinase was determined and our results demonstrated a significant drop in H1 activity in the activated oocytes. The cleavage of parthenogenetic embryos progresses to more advanced stages after stimulation by IP3R than after stimulation by RyR. Our results could indicate that, in pig oocytes, the calcium released from IP3-sensitive stores triggers the calcium release from ryanodine-sensitive intracellular stores, which is necessary for oocyte activation. The calmodulin inhibitors ophiobolin A and W7 reduce the activation of oocytes induced by stimulation of RyR or IP3R.