Free calcium increases explosively in activating medaka eggs.

Publisher Website
Google Scholar
Abstract
The Ca-specific light-emitting protein aequorin was used to follow changes in free Ca concentration during fertilization and cleavage of eggs from medaka [Oryzias latipes], a fresh-water fish. Aequorin-injected medaka eggs show a very low resting glow before they are fertilized, indicating a low Ca concentration in the resting state. Upon activation by sperm the Ca-mediated light emission increased to a level some 10,000 times the resting level with a 1-2 s time constant for an 3-fold increase and then slowly returned to the resting level. Upon activation by the ionophore A23187, the early rise in luminescence was much slower, but once a threshold was reached the subsequent rise became as rapid as the normal sperm-induced response. The explosive rise in Ca probably involved Ca-stimulated Ca release and a sperm normally triggered this rise by somehow inducing a more modest and localized rise in Ca.