Glycine uptake in pre-implantation mouse embryos: kinetics and the effects of external [Na+].
The kinetic parameters (with standard errors) describing glycine uptake by mouse 2-cell embryos and blastocysts were determined by non-linear regression. Uptake at both stages was best described by a combination of a non-saturable component and a single saturable uptake system. During development, the rate constants for both components increased, as would be expected from the known increases in surface area, from 9.4 +/- 3.7 pL per 10 min per embryo and 128 +/- 12 fmol per 10 min per embryo in 2-cell embryos to 38.9 +/- 2.1 pL per 10 min per embryo and 258 +/- 15 fmol per 10 min per embryo in blastocysts. In contrast to earlier reports, there was no change in Km, which was 88 +/- 13 microM in 2-cell embryos and 115 +/- 10 microM in blastocysts. Reducing the external [Na+] from 230 mM increased Km for both stages. This effect on Km appeared to be related to [Na+]-2 or [Na+]-3. Vmax was increased in embryos of both stages by increasing [Na+] from 60 to 100 mM. However, whilst further increases to 400 mM were without major effect on uptake by 2-cell embryos, they inhibited uptake by blastocysts. This may result from osmotic effects on trophectodermal transport in the blastocysts. These results suggest that during development to blastocysts, the gly-system that operates in 2-cell embryos may be modified to a less restricted system with a similar Km and a complex dependence on [Na+].
Hobbs
J G
JG
Department of Physiology and Pharmacology, University of Queensland, Australia.
Kaye
P L
PL
D000818:Animals; D001755:Blastocyst / Q000378:metabolism*; D002712:Chlorides / Q000494:pharmacology; D002794:Choline / Q000494:pharmacology; D004305:Dose-Response Relationship, Drug; D047108:Embryonic Development / Q000502:physiology*; D005260:Female; D005998:Glycine / Q000493:pharmacokinetics*; D066298:In Vitro Techniques; D008094:Lithium / Q000494:pharmacology; D018021:Lithium Chloride; D051379:Mice; D011247:Pregnancy; D012964:Sodium / Q000494:pharmacology*; D012965:Sodium Chloride / Q000494:pharmacology
D002712:Chlorides; D012965:Sodium Chloride; D008094:Lithium; D012964:Sodium; D018021:Lithium Chloride; D002794:Choline; D005998:Glycine