Glycine and Na+ transport in preimplantation mouse embryos

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Abstract
The dependence of glycine uptake on glycine and Na+ concentration was determined and compared in 2-cell embryos and blastocysts. In both, uptake was by a combination of a Na+-independent non-saturable route and a Na+-dependent saturable system with Km values of 62 .mu.M and 274 .mu.M for 2-cell embryos and blastocysts respectively. Na+-dependent saturable uptake by embryos of both stages had a Hill coefficient of 2 for Na+, indicating co-transport of 2 Na+ with each glycine molecule. These results suggest that glycine enters 2-cell embryos by the gly-system, and blastocysts by a similarly Na+-dependent system with characteristics resembling the A-system.