Hypoxia regulates glutamate metabolism and membrane transport in rat PC12 cells.
We investigated the effect of hypoxia on glutamate metabolism and uptake in rat pheochromocytoma (PC12) cells. Various key enzymes relevant to glutamate production, metabolism and transport were coordinately regulated by hypoxia. PC12 cells express two glutamate-metabolizing enzymes, glutamine synthetase (GS) and glutamate decarboxylase (GAD), as well as the glutamate-producing enzyme, phosphate-activated glutaminase (PAG). Exposure to hypoxia (1% O(2)) for 6 h or longer increased expression of GS mRNA and protein and enhanced GS enzymatic activity. In contrast, hypoxia caused a significant decrease in expression of PAG mRNA and protein, and also decreased PAG activity. In addition, hypoxia led to an increase in GAD65 and GAD67 protein levels and GAD enzymatic activity. PC12 cells express three Na(+)-dependent glutamate transporters; EAAC1, GLT-1 and GLAST. Hypoxia increased EAAC1 and GLT-1 protein levels, but had no effect on GLAST. Chronic hypoxia significantly enhanced the Na(+)-dependent component of glutamate transport. Furthermore, chronic hypoxia decreased cellular content of glutamate, but increased that of glutamine. Taken together, the hypoxia-induced changes in enzymes related to glutamate metabolism and transport are consistent with a decrease in the extracellular concentration of glutamate. This may have a role in protecting PC12 cells from the cytotoxic effects of glutamate during chronic hypoxia.
Kobayashi
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Department of Molecular and Cellular Physiology, University of Cincinnati, OH 45267, USA.
Millhorn
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D018528:ATP-Binding Cassette Transporters / Q000378:metabolism; D000310:Adrenal Gland Neoplasms; D027322:Amino Acid Transport System X-AG; D000818:Animals; D001692:Biological Transport; D002352:Carrier Proteins / Q000378:metabolism; D015687:Cell Hypoxia / Q000502:physiology*; D002462:Cell Membrane / Q000378:metabolism*; D027341:Excitatory Amino Acid Transporter 1; D050580:Excitatory Amino Acid Transporter 3; D015971:Gene Expression Regulation, Enzymologic; D015972:Gene Expression Regulation, Neoplastic; D005968:Glutamate Decarboxylase / Q000235:genetics / Q000378:metabolism; D050491:Glutamate Plasma Membrane Transport Proteins; D005974:Glutamate-Ammonia Ligase / Q000235:genetics / Q000378:metabolism; D018698:Glutamic Acid / Q000378:metabolism*; D005972:Glutaminase / Q000235:genetics / Q000378:metabolism; D007527:Isoenzymes / Q000235:genetics / Q000378:metabolism; D016716:PC12 Cells; D010673:Pheochromocytoma; D051381:Rats; D020133:Reverse Transcriptase Polymerase Chain Reaction; D027981:Symporters
D018528:ATP-Binding Cassette Transporters; D027322:Amino Acid Transport System X-AG; D002352:Carrier Proteins; D027341:Excitatory Amino Acid Transporter 1; D050580:Excitatory Amino Acid Transporter 3; D050491:Glutamate Plasma Membrane Transport Proteins; D007527:Isoenzymes; C493398:Slc1a1 protein, rat; C493392:Slc1a3 protein, rat; D027981:Symporters; D018698:Glutamic Acid; D005972:Glutaminase; D005968:Glutamate Decarboxylase; C402565:glutamate decarboxylase 1; C401141:glutamate decarboxylase 2; D005974:Glutamate-Ammonia Ligase