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Electrical maturation of the murine oocyte: an increase in calcium current coincides withacquisition of meiotic competence

Published online by Cambridge University Press:  26 September 2008

Joan M. Murnane  and
Louis J. DeFelice
Joan M. Murnane
Affiliation:
Emory University School of Medicine, Atlanta, Georgia, USA
Louis J. DeFelice*
Affiliation:
Emory University School of Medicine, Atlanta, Georgia, USA
*
Louis J. DeFelice, Department of Anatomy and Cell Biology, Emory University School of Medicine, Atlanta, GA 30322, USA.
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Summary

We have used the whole-cell recording technique to compare three stages of primary and secondary oocytes from F1 hybrid mice (C57BL/6J x SJL/J):neonatal germinal vesicle (NGV) stage primary oocytes from 10- to 20-day-old, prepubescent mice; mature germinal vesicle (MGV) stage primary oocytes from 12-week-old, post-pubescent, superovulated mice; first polar body (FPB) stage secondary oocytes from 12-week-old, post-pubescent mice during the normal oestrus cycle or following superovulation. NGV, MGV and FPB oocytes all exhibit two voltage-dependent currents: an inward, rapidly activating/inactivating current, and an outward, slowly activating/non-inactivating current. In 1.5 mmol/1 external Ca the average peak inward current is − 2.9, − 12.4 and − 13.8 μA/cm2 in NGV, MGV and FPB oocytes, respectively. In 20 mmol/1 Ca these currents increase and the reversal potential shifts to the right. The outward current decreases slightly with growth and development: at 40 mV test potentials, NGV oocytes have average outward currents of 8.9 μA/cm2, and MGV and FPB oocytes have currents of 5.0 and 5.5 μA/cm2, respectively. Thus, MGV oocytes express FPB current patterns. The reversal potentials, kinetics and pharmacology of the currents indicate that Ca channels carry the inward current and K channels carry the outward current. During growth in vivo a gradual depolarisation accompanies maturation. Resting potentialsranged from − 45 to − 30 mV in NGV oocytes to − 35 to − 17 mV in MGV oocytes to − 20 mV to − 3 mV in FPB oocytes. These data suggest that a selective increase occurs in the number of Ca channels during oocyte growth. This increase precedes nuclear maturation and coincides with the acquisition of meiotic competence.

Keywords

Oocyte maturationcalcium channelswhole-cell voltage clampmeiotic competence
Type
Article
Information
Zygote , Volume 1 , Issue 1 , February 1993 , pp. 49 - 60
Copyright
Copyright © Cambridge University Press 1993

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