REGULATION OF NA- ROLE OF CALCIUM(, K+ ATPASE ACTIVITY DURING MEIOTICMATURATION OF PLEURODELES WALTL OOCYTES )

Changes in activity of the Na+,K+ ATPase of maturing Pleurodeles waltl were followed by measuring the resting potential in presence or absen ce of the specific inhibitor dihydroouabain. Corresponding currents we re measured in voltage clamp conditions to eliminate the differences i n resting potential at the origin and at the end of the meiotic matura tion process. Our data confirm previous results obtained on Xenopus, i ndicating that the Na+,K+ pump activity disappears from the plasma mem brane during progesterone-induced maturation and can be reactivated by an increase in internal Ca2+ triggered by ionomycin. Moreover we show by ultrastructural histochemistry that these modulations are likely t o depend on the internalization and reinsertion of the transporter int o the plasma membrane.