Regulation of the glutamate transporter by amino acid deprivation and associated effects on the level of EAAC1 mRNA in the renal epithelial cell line NBL-I

Abstract

The glutamate transport system of the bovine renal epithelial cell line NBL-1 was studied. The Km for Na(+)-dependent glutamate transport was found to be 13.8 +/- 2.4 microM (Vmax. 365 +/- 19.2 pmol/3 min per mg) and for Na(+)-dependent aspartate transport 4.5 +/- 1.1 microM (Vmax. 108 +/- 6.3 pmol/3 min per mg). The Km values are in close agreement with those expected for high-affinity Na(+)-dependent glutamate transport by System XAG-. Upon deprivation of amino acids, the Vmax. for Na+/aspartate co-transport rose to 203 +/- 6.0 pmol/3 min per mg (Km 3.8 +/- 0.5 microns). 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.