THE PERMEABILITY OF TWO- AND EIGHT-CELL MOUSE EMBRYOS TO l-MALIC ACID

Summary. The level of radio-isotope in 2- and 8-cell mouse embryos was measured following a 30-min incubation in isotopically labelled malate. Although there was very little accumulation of substrate carbon and no output of radio-active carbon dioxide by 2-cell embryos, 8-cell embryos accumulated substrate carbon during the incubation and oxidized some of the malate to carbon dioxide. A change in the concentration of malate in the medium and the addition of ouabain had little effect on the accumulation of substrate in 8-cell embryos. On the other hand, its accumulation was suppressed during incubations at 5° C. The evidence suggests that there is little or no uptake of malate by 2cell embryos, and that an active uptake of the compound occurs at a later stage of development.