Free calcium increases explosively in activating medaka eggs.
We have used the calcium-specific light-emitting protein aequorin to follow changes in free calcium concentration during fertilization and cleavage of eggs from medaka, a fresh-water fish. Aequorin-injected medaka eggs show a very low resting glow before they are fertilized, indicating a low calcium concentration in the resting state. Upon activation by sperm, the calcium-mediated light emission increases to a level some 10,000 times the resting level with a 1 to 2 sec time constant for an e-fold increase, and then slowly retruns to the resting level. Upon activation by the ionophore A23187, the early rise in luminescence is much slower, but once a threshold has been reached the subsequent  rise becomes as rapid as the normal sperm-induced response. We infer that the explosive rise in calcium involves calcium-stimulated calcium release, and that a sperm normally triggers this rise by somehow inducing a more modest and localized rise in calcium.
D000331:Aequorin / Q000494:pharmacology; D000818:Animals; D000001:Calcimycin / Q000494:pharmacology; D002118:Calcium / Q000378:metabolism*; D005260:Female; D005306:Fertilization; D005399:Fishes; D008163:Luminescent Measurements; D008297:Male; D009865:Oocytes / Q000187:drug effects / Q000378:metabolism* / Q000502:physiology; D010063:Ovum / Q000378:metabolism*; D013094:Spermatozoa / Q000502:physiology
D000001:Calcimycin; D000331:Aequorin; D002118:Calcium