Characterization of glutamine uptake in mouse two-cell embryos and blastocysts

Mouse two-cell embryos and blastocysts take up [3H]glutamine in vitro at a constant rate for at least 15 min, depending on the concentration of glutamine and developmental stage of the embryo. Uptake by two-cell embryos can be resolved into two saturable components. The major contributing system is Na+ independent, inhibited by alanine, methionine, 2-amino-2-norbornanecarboxylic acid (BCH) or leucine and has a Km of 3856 +/- 672 mumols l-1 and Vmax of 436 +/- 58 fmol per embryo per 10 min. These features are characteristics of the ubiquitous system L transporter. The second component is Na+ dependent with Km of 1064 +/- 914 mumols l-1 and Vmax 107 +/- 47 fmol per embryo per 10 min. Similar Vmax and inhibition of this component by glycine suggest a low reactivity with the gly-system. Blastocyst uptake of glutamine is mainly by a Na(+)-dependent saturable mechanism with Km of 524 +/- 75 mumols l-1 and Vmax of 1264 +/- 101 fmol per embryo per 10 min which is inhibited by alanine, isoleucine, leucine and BCH, features characteristic of the system B0,+. The increase in uptake capacity as a consequence of the appearance of the system B0,+ may be related to increased metabolic requirements for glutamine, in the rapidly expanding blastocyst.