Aspartate and glutamate transport in unfertilized pig oocytes and blastocysts.

Amino acid transport is facilitated by specific transporters within the plasma membrane of the cell. Mediated Na(+)-independent transport of L-glutamate can be easily detected in mouse oocytes, but it is nearly undetectable in blastocyst-stage embryos. In contrast, the Na(+)-dependent transport of L-aspartate is not detectable in oocytes, but it is detectable in eight-cell embryos and reaches relatively high levels by the blastocyst stage. It is believed that the amino acid transporters responsible are systems x-c and X-AG, respectively. Here we report the detection of Na(+)-dependent L-aspartate transport, which increased as pig blastocysts developed, although Na(+)-dependent aspartate transport was not detected in pig oocytes. Mediated Na(+)-independent L-glutamate transport was not detected in pig oocytes, in contrast to the mouse, nor in early or hatched pig blastocysts. Thus, while the developmental regulation of system X-AG is similar in both the pig and the mouse, system x-c was not detectable in pig oocytes or blastocysts. Elucidation of the molecular mechanisms controlling amino acid transport and other gene expression in early embryos should contribute to an understanding of whether and even why some aspects of developmental regulation of gene expression may need to differ among species.