Free Calcium Increases Explosively in Activating Medaka Eggs
Abstract
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 returns 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.
- Publication:
-
Proceedings of the National Academy of Science
- Pub Date:
- February 1977
- DOI:
- 10.1073/pnas.74.2.623
- Bibcode:
- 1977PNAS...74..623R