However, cortical reaction, not nuclear activation, was induced with A23187 in Ca2+-free medium in mouse oocytes, indicating that extracellular calcium is necessary for full activation of the oocytes. Calcium transients were not observed in pig oocytes either by electrical pulse or A23187 (data not shown) in Ca2+-free medium. It is possible that the mechanisms of oocyte activation by A23187 or other artificial stimulations are different among species. Our present results indicate that A23187-induced Ca2+ transients started with a gradual increase phase and this increase reached the peak value within 60-160 sec, depending on the concentration of A23187 used, and then showed a very slow recovery phase that lasted 1-3 min. levitra super active plus
When the oocytes were washed and then measured again, no other transients could be detected. These results indicate that these Ca2+ transients are the result of A23187-induced extracellular influx, and the Ca2+-induced Ca2+ release, which was hypothesized in sperm-penetrated oocytes, is not present in these artificially activated pig oocytes, present study). These differences have also been observed in other mammals.