Glycine transport by single human and mouse embryos

Mouse zygotes and early cleavage-stage embryos have previously been shown t o utilize glycine as an organic osmolyte, accumulating it to oppose any dec rease in cell volume. Such glycine uptake in early cleavage-stage mouse emb ryos is via the glycine-specific Gly transporter. Mouse embryos also posses s swelling-activated channels which function to release osmotically active glycine and other osmolytes when cell volume becomes too large. In this stu dy it was found that human cleavage-stage embryos also transported glycine via a similarly saturable, sarcosine-inhibitable transporter, implying that the Gly transporter also mediates glycine transport in human embryos, Mous e zygotes have previously been shown to accumulate more intracellular glyci ne when cultured at increased osmolarities for 24 h, It was found in the cu rrent study that this ability was lost as preimplantation mouse embryo deve lopment proceeded, and that early cleavage-stage human embryos may also be capable of such osmosensitive accumulation of glycine. Finally; using spare human eggs which had failed to fertilize or cleave, the presence of swelli ng-activated currents resembling those in mouse zygotes was demonstrated. T hese data indicate that osmoregulation in early human embryos occurs via si milar mechanisms as in the mouse.