INDUCTION OF HIGH-AFFINITY GLUTAMATE TRANSPORT ACTIVITY BY AMINO-ACIDDEPRIVATION IN RENAL EPITHELIAL-CELLS DOES NOT INVOLVE AN INCREASE INTHE AMOUNT OF TRANSPORTER PROTEIN

In renal epithelial cells amino acid deprivation in duces an increase in L-Asp transport with a doubling of the V-max and no change in K-m ( 4.5 mu M) in a cycloheximide-sensitive process. The induction of sodiu m-dependent L-aspartate transport was inhibited by single amino acids that are metabolized to produce glutamate but not by those that do not produce glutamate. The transaminase inhibitor aminooxyacetate in glut amine free medium caused a decrease in cell glutamate content and an i nduction of glutamate transport. In complete medium aminooxyacetate ne ither decreased cell glutamate nor increased transport activity. These results are consistent with a triggering of induction of transport by low intracellular glutamate concentrations. High affinity glutamate t ransport in these cells is mediated by the excitatory amino acid carri er 1 (EAAC1) gene product. Western blotting using antibodies to the C- terminal region of EAAC1 showed that there is no increase in the amoun t of EAAC1 protein on prolonged incubation in amino acid-free medium. Conversely, the induction of high affinity glutamate transport by hype rosmotic shock was accompanied by an increase in EAAC1 protein. It is proposed that low glutamate levels lead to the induction of a putative protein that activates the EAAC1 transporter. A model illustrating su ch a mechanism is described.