J. Cell Biol. The rapid, transient, influx of sodium ions depolarizes the egg's membrane potential establishes the fast block to polyspermy. The slower, permanent, block to polyspermy is established by the fusion of the cortical vesicles with the plasma membrane. To see the wave of release of calcium ions in eggs, they are injected with aequorin, a protein that emits light when it binds to calcium ions. In the last sequence, an unfertilized egg with aequorin is exposed to an ionophore that makes the egg permeable to calcium ions in the medium.
All sequences are approximately twice as fast as they actually occur.
We welcome your comments and suggestions for the Developmental Biology Cinema.