Neutral amino acid influx in developing rabbit blastocysts

Abstract

The influx of the neutral amino acids glycine, aminoisobutyric acid (AIB), and leucine into rabbit blastocysts was measured. In day 6 postcoitus (pc) embryos, glycine influx was Na+ independent, whereas AIB and leucine influx involved both Na+-dependent and independent components. From days 5 to 7 pc, the leucine and AIB influx remained constant, although the Na+-dependent fraction decreased and the Na+-independent fraction increased with age. None of the Na+-independent influx was inhibited by methylaminoisobutyric acid (MeAIB), an amino acid analogue specific for the system A of neutral amino acid uptake. In addition, MeAIB influx was Na+ independent, implying that system A is not involved in leucine or AIB uptake. All Na+-dependent influx is thus considered to occur via system ASC. System L contributed only to the influx of leucine at days 6 and 7 pc, as measured by inhibition of Na+-independent influx by 2-amino-bicyclo-(2,2,1)-heptane-2-carboxylic acid.