Change in Intracellular Calcium Ions upon Maturation in Starfish Oocytes: (aequorin/calcium/oocyte...

A transient increase in intracellular Ca2+ upon maturation in starfish oocyte was revealed by light emission of aequorin microinjected into the cell. One minute application of 1-methyladenine (1-MeAde) to a limited area of the oocyte surface was sufficient to induce the Ca2+ transient over the entire cell though it did not induce the germinal vesicle breakdown (GVBD). Ten minutes application of 1-MeAde induced a similar Ca2+ transient followed by GVBD. Even when the transient increase of Ca2+ was inhibited by injecting EGTA into the oocyte, 1-MeAde treatment for a long period induced GVBD. These facts indicate that the Ca2+ increase is neither necessary nor sufficient for maturation of the starfish oocyte. When the oocyte, which had been treated with 1-MeAde for 1 min at a limited area around the animal pole, was treated again with 1-MeAde for 10 min starting about 15 min after the first treatment, a Ca2+ transient similar to the first one was induced and was followed by GVBD. By contrast, in the oocyte treated with 1-MeAde at an area around the vegetal pole, neither Ca2+ transient nor GVBD was induced by the second treatment with 1-MeAde. These results indicate a difference in responsiveness to the hormone between the animal hemisphere and the vegetal hemisphere of the oocyte.