Change in Intracellular Calcium Ions upon Maturation in Starfish Oocytes: (aequorin/calcium/oocyte maturation/1-methyladenine/starfish).

A transient increase in intracellular Ca 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 Ca transient over the entire cell though it did not induce the germinal vesicle breakdown (GVBD). Ten minutes application of 1-MeAde induced a similar Ca transient followed by GVBD. Even when the transient increase of Ca was inhibited by injecting EGTA into the oocyte, 1-MeAde treatment for a long period induced GVBD. These facts indicate that the Ca 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 Ca 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 Ca 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.