Oxidative phosphorylation-dependent and -independent oxygen consumption byindividual preimplantation mouse embryos

The self-referencing electrode technique was employed to noninvasively meas ure gradients of dissolved oxygen in the medium immediately surrounding dev eloping mouse embryos and, thereby, characterized changes in oxygen consump tion and utilization during development. A gradient of depleted oxygen surr ounded each embryo and could be detected >50 mu m from the embryo. Blastocy sts depleted the surrounding medium of 0.6 +/- 0.1 mu M of oxygen, whereas early cleavage stage embryos depleted the medium of only 0.3 +/- 0.1 mu M o f oxygen, suggesting a twofold increase in oxygen consumption at the blasto cyst stage. Mitochondrial oxidative phosphorylation (OXPHOS) accounted for 60-70% of the oxygen consumed by blastocysts, while it accounted for only 3 0% of the total oxygen consumed by cleavage-stage embryos. The amount of ox ygen consumed by non-OXPHOS mechanisms remained relatively constant through out preimplantation development. By contrast, the amount of oxygen consumed by OXPHOS in blastocysts is greater than that consumed by OXPHOS in cleava ge-stage embryos. The amount of oxygen consumed by one-cell embryos was mod ulated by the absence of pyruvate from the culture medium. Treatment of one -cell embryos and blastocysts with diamide, an agent known to induce cell d eath in embryos, resulted in a decline in oxygen consumption, such that the medium surrounding dying embryos was not as depleted of oxygen as that sur rounding untreated control embryos. Together these results validate the sel f-referencing electrode technique for analyzing oxygen consumption and util ization by preimplantation embryos and demonstrate that changes in oxygen c onsumption accompany important physiological events, such as development, r esponse to medium metabolites, or cell death.