Hypertonic Stress and Amino Acid Deprivation Both Increase Expression of mRNA for Amino Acid Transport System A

The activity of amino acid transport system A (Oxender and Christensen, 1963) is regulated in a variety of different ways, the best studied being the increases of its activity caused by starving cells of amino acids or by exposing them to hypertonicity (for review see McGivan and Pastor-Anglada, 1994). Recently, López-Fontanals et al. (2003) reported in the Journal of General Physiology that hypertonic activation of system A in Chinese hamster ovary (CHO-K1) cells, in contrast to its activation by amino acid deprivation, did not involve increased transcription of the mRNA for one of the system A isoforms. We shall follow the suggestion of Mackenzie and Erickson (2004) and call the isoform SNAT2, for sodium-coupled neutral amino acid transporter 2, instead of ATA2 or SAT2 or SA1. This finding supported a scheme, proposed before the cloning of system A, that features basically different...