Changes in the activities of amino acid transport systems b0,+ and L during development of preimplantation mouse conceptuses.
Uptake of leucine, lysine, and arginine was predominantly Na(+)-independent in mouse conceptuses through the 8-cell stage of development, and two components of saturable transport were detected for each of these amino acids. Uptake of cationic substrates from solutions near 1 microM was inhibited most strongly by bulky cationic and zwitterionic amino acids whose carbon skeletons do not branch at the alpha or beta positions. By this criterion, system b0,+ accounted for most of the Na(+)-independent arginine and lysine transport in eggs and conceptuses throughout preimplantation development. A small, leucine-resistant, cation-preferring component of amino acid transport was also detected in these cells. Leucine uptake was inhibited most strongly by bicyclic, branched-chain or benzenoid, zwitterionic amino acids in eggs and conceptuses prior to formation of blastocysts. Therefore, it appeared to be taken up mainly by system L, while system b0,+ accounted for a smaller portion of leucine uptake during this developmental period. In blastocysts, in contrast, system L was less conspicuous, and system b0,+ was primarily responsible for Na(+)-independent leucine uptake. The Vmax values for transport of amino acids by system b0,+ increased by up to 30-fold in conceptuses between the 1-cell and blastocyst stages. In contrast, the Vmax value for leucine transport via system L decreased while the Km value increased between these two developmental stages. Although several explanations for these changes are possible, we favor the hypothesis that the density of system L transport sites in plasma membranes decreases while the number of system b0,+ sites increases during development of blastocysts from 1-cell conceptuses.
Van Winkle
L J
LJ
Department of Biochemistry, Chicago Osteopathic Health Systems/CCOM, Downers Grove, IL 60515.
Campione
A L
AL
Gorman
J M
JM
Weimer
B D
BD
D000596:Amino Acids / Q000493:pharmacokinetics*; D000818:Animals; D001120:Arginine / Q000493:pharmacokinetics; D001692:Biological Transport; D001755:Blastocyst / Q000378:metabolism*; D007930:Leucine / Q000493:pharmacokinetics; D008239:Lysine / Q000493:pharmacokinetics; D051379:Mice; D010063:Ovum / Q000378:metabolism; D012964:Sodium / Q000494:pharmacology
D000596:Amino Acids; D001120:Arginine; D012964:Sodium; D007930:Leucine; D008239:Lysine