Inner mitochondrial membrane potential (ΔΨm), cytoplasmic ATP content and free Ca2+ levels in metaphase II mouse oocytes

Abstract

Background: The relative magnitude of the inner mitochondrial membrane potential (ΔΨm) has been suggested to indicate the competence of mammalian gametes and early embryos. This study examined the response of cultured somatic cells and mouse oocytes to inhibitors and conditions that affect ΔΨm or metabolism, or both, and measured treatment-specific changes in ATP and cytoplasmic free Ca2+. Methods: During and after treatment, relative ΔΨm, free Ca2+, and ATP levels and cortical granule density were determined. Results: Comparable responses of somatic cells and metaphase II mouse oocytes to experimental manipulations that affect ΔΨm and metabolism were observed and reversible loss of ΔΨm was associated with increased intracellular free Ca2+, which in certain instances resulted in parthenogenetic activation. Conclusion: The findings support a mitochondrial basis for pericortical J-aggregate fluorescence but not for a direct association between high ΔΨm and metabolism. The results extend previous findings indicating that high-polarized (high ΔΨm, JC-1 J-aggregate-forming) mitochondria occur in pericortical domains in mouse and human oocytes and early preimplantation stage embryos and support the notion that this spatial distribution may be related to localized ionic and metabolic regulation.