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〔Sumiyoshi&Ginza〕Calcium Ionophore

 

Calcium Ionophore(Ca2+ ionophore) is the generic name for a substance that enhances the permeability of calcium ions in the cell membrane. In ART it is used to cause the activation of the egg. It is used in cases of failure of conception and in severe male infertility.
Fertilization happens when each nucleus fuses with the sperm inside the egg.
First the sperm enters the oocyte and passes through the "shell" (transparent layer), entering the egg and adheres to the cell membrane. Then, a substance called PLCζ that the sperm has will increase the calcium in the egg. Calcium continues to spread within the egg, and the egg will activate. This wave of calcium will repeat itself, followed by a certain period of time(calcium oscillation). Various changes occur in the egg, two pro-nucleus(egg-derived genes and sperm-derived genes are in them) are formed, and finally fertilization is complete when the two are fused together.

 

 

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Calcium oscillation

 

 

1) Passing through the transparent layer

Enzymes (hyaluronidase) from the sperm head will leave and dissolve the transparent zone(zona pellucida), and enter inside the transparent layer (perivitelline space).

 

Passing through the transparent layer

2) Membrane fusion

The sperm will adhere to the cell membrane of the oocyte. At this point, the penetration of other sperm is blocked. Egg activation substance (PLCζ) is released from the sperm.

Membrane fusion

3) Egg activation

PLCζ causes the release of calcium from the endoplasmic reticulum of the egg cytoplasm.
Calcium is spread in a wave in the egg cytoplasm.
When the egg is activating during this process (calcium oscillation), it will continue until the pro-nuclear period.
During this time, the meiosis of the egg and the second polar body release, the collapse and re-aggregation of the sperm nuclear membrane occurs.

Egg activation

4) 2 Pronuclear formation ˜ Before fusion

The female pro-nucleus with the genes derived from the eggs and the male pro-nucleus with the genes derived from the sperm are formed. Finally when the two nuclei are joined then the fertilization is complete.

2 Pronuclear formation ˜Before fusion

 

In the case of ICSI, when the sperm is injected into the egg by the needle the egg will activate, but because PLCζ release is bypassed from the membrane fusion, an increase in calcium is required for the activation of the ovum, this might be insufficient. When this happens, calcium ionophore is key. Calcium ionophore encourages an increase in the calcium concentration in the egg cytoplasm, and then induces egg activation after ICSI.

 

 

 

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