Energy requirements of the developing mammalian blastocyst for active ion transport.

Abstract

ABST RACT 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) Qo,, when expressed per unit blastocyst surface area, is 4 p1 O ‘cm2 ‘h-’ in both Day 4 and 5 postcoitus (p.c.) embryos, and 2.7 p1 02 ‘cm2 h-’ 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.