Electrophoretic quantification of the changes in the average net negative surface charge density of mouse blastocysts implanting in vivo and in vitro.

An apparatus for free-zone electrophoresis was used to measure changes in the zeta potential or net negative surface charge density of mouse blastocysts. Delayed (inactive) and implanting blastocysts, recovered from the uterine cavity, were analyzed before and after incubation with neuraminidase. Growth-arrested and growth-activated blastocysts, obtained by blastocyst culture, were also examined. The results showed that the net negative surface charge density of the blastocysts decreased by 30% at implantation and at growth in culture, suggesting that the changes of the blastocyst surface at implantation are intrinsic cell membrane changes, and not caused by environmental alterations. The neuraminidase treatment decreased the net negative charge density of both delayed and implanting blastocysts by 30-60%. Thus the influence of this treatment varied too greatly among the blastocysts to permit any conclusions to be drawn about differences in the total amount of sialic acid between delayed and implanting blastocysts. Further, both delayed and implanting blastocysts carried negatively charged groups other than sialic acid containing ones. Scanning electron microscopy revealed surface changes on the blastocysts both after electrophoresis and after neuraminidase incubation; the former changes were probably normally occurring contractions, while the latter represented true alterations of the cell surface.