REGULATION OF THE GLUTAMATE TRANSPORTER BY AMINO-ACID DEPRIVATION AND ASSOCIATED EFFECTS ON THE LEVEL OF EAAC1 MESSENGER-RNA IN THE RENAL EPITHELIAL-CELL LINE NBL-1

The glutamate transport system of the bovine renal epithelial cell line NBL-1 was studied. The K(m) for Na+-dependent glutamate transport was found to be 13.8 +/- 2.4 muM (V(max) 365 +/- 19.2 pmol/3 min.per mg) and for Na+-dependent aspartate transport 4.5 +/- 1.1 muM (V(max) 108 +/- 6.3 pmol/3 min per mg). The K(m) values are in close agreement with those expected for high-affinity Na+-dependent glutamate transport by System X(AG-.) Upon deprivation of amino acids, the V(max) for Na+/aspartate co-transport rose to 203 +/- 6.0 pmol/3 min per mg (K(m) 3.8 +/- 0.5 mum). A probe was constructed to the high-affinity excitatory amino acid carrier (EAAC1) [Kanai and Hediger (1992) Nature (London) 360, 467-471]. The probe hybridized to a 3.5 kb transcript. On deprivation of amino acids, the level of EAAC1 mRNA decreased sharply before the measurable increase in transport levels, but was subsequently restored to control levels. A motif, which we propose is linked to amino acid deprivation, was found in the EAAC1 primary sequence.