Maturation of Xenopus oocytes is not accompanied by electrode-detectable calcium changes

Ca2+-sensitive microelectrodes were used to study changes in cytoplasmic free calcium during progesterone-induced meiotic maturation in Xenopus laevis oocytes. In contrast to previous reports, no changes were detected during the maturation process, although a large activation pulse of Ca2+ was seen when in vitro matured eggs were parthenogenetically activated. The resting level of Ca2+ in the oocytes was 0.14 microM +/- 0.05.