Regulation of high-affinity glutamate transport by amino acid deprivation and hyperosmotic stress

High-affinity glutamate transport activity is induced by stress in NBL-1 ce lls. Exposure of cells to hyperosmotic medium led to an induction of the EA AC1 glutamate transporter, preceded by a large increase in EAAC1 mRNA level s. Culture of cells in amino acid-free medium also caused a protein synthes is-dependent increase in glutamate transport activity, but this was not acc ompanied by an increase of either EAAC1 mRNA or protein. Indirect evidence suggests that the increase in EAAC1 activity in the latter case may be due to the synthesis of an activator protein in response to decreased intracell ular glutamate concentrations.