Biology of Reproduction, Vol 23, 941-947, Copyright © 1980 by Society for the Study of Reproduction

Energy Requirements of the Developing Mammalian Blastocyst for Active Ion Transport

¹ Department of Physiology and Laboratory of Human Reproduction and Reproductive Biology, Harvard Medical School, Boston, Massachusetts 02115
² Department of Biochemistry, University of Oxford, Oxford OX1 3QU, England, U.K.

The aerobic dependence of active transepithelial ion transport in preimplantation rabbit blastocysts of different ages was studied. The rate of oxygen consumption (Qo₂) of the blastocysts was determined in the absence or presence of various transport and metabolic inhibitors and stimulators to ascertain the degree of coupling between the aerobic conversion of energy and active ion transport in this rapidly developing system. The results demonstrate that 1) Qo₂, when expressed per unit blastocyst surface area, is 4 µl O₂·cm^-2·h^-1 in both Day 4 and 5 postcoitus (p.c.) embryos, and 2.7 µl O₂·cm^-2·h^-1 in Day 6 and 7 p.c. blastocysts; 2) the respiratory rate appears to be near its maximum, since Qo₂ could not be stimulated by the uncouplers CCCP or DNP; 3) Qo₂ appears to be substrate-limited in this system; and 4) a large fraction (up to 0.7) of the total Qo₂ supports active ion transport during the period 4 to 6 days p.c., but this fraction is drastically reduced (to 0.16) at Day 7 p.c., the day of implantation.

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ACKNOWLEDGMENTS We thank Ms. Marie Blazonis for her excellent technical assistance, and M. J. Kushmerick and L. Role for helpful discussions. This work was supported by NIH Grant HD 12353 from NICHHD and by funds provided by the Andrew W. Mellon Foundation.

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