Describe a well-controlled experiment to determine if the rise in internal free calcium observed in the cytoplasm of unfertilized sea urchin eggs in the presence of A23187 is due to in flux of calcium from seawater. Include experimental treatments, controls, and briefly describe experimental methods.
Note: As mentioned in the lab manual, the calcium concentration in seawater is 10mM while the concentration in unfertilized egg cytoplam is greater that 10-6 M. Immediately after fertilization or in unfertilized eggs treated with A23187 the internal calcium concentration increases.
This is a very interesting experiment and I have performed it several times with students in a developmental biology lab.
Fertilization triggers a release of calcium that activates the signaling pathways necessary to trigger the fast and slow block. These blocks are important because they prevent polyspermy (fertilization of an egg by multiple sperm that results in abnormal chromosome numbers and uneven centriole content). A23187 is an ionophore that triggers the release of calcium. There are two hypotheses as to where this calcium is originating, outside of the egg or from calcium stores within the egg.
Explanation of the calcium signaling that occurs during fertilization and the experiment to determine the origin of this calcium is provided.