[Oocyte maturation in Xenopus laevis. Arguments in favor of the role of calcium ions].

Influx and efflux of 45Ca++ ions in Xenopus leavis isolated full-grown oocytes were measured. Calcium influx was from 0.5 to 1 pmole/oocyte/h. Progesterone, which induces maturation does not influence Ca++ fluxes while PCMB caused a significant increase of Ca++ influx during the course of PCMB (p-Cl-HgBzO-) induced maturation. Our results show that the presence of Ca++ is not necessary in extracellular medium for germinal vesicle breakdown (GVBD) induced by progesterone. In contrast, the kinetic and the percent of germinal vesicle breakdown observed when maturation was induced by PCMB depend on the extracellular Ca++ concentration in Ca-EGTA buffers.