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High sensitivity of glutamate uptake to extracellular free arachidonic acid levels in rat cortical synaptosomes and astrocytes
Journal of Neurochemistry
Journal Article --- Old month value: Aug
By using both synaptosomes and cultured astrocytes from rat cerebral cortex, we have investigated the inhibitory action of arachidonic acid on the high-affinity glutamate uptake systems, focusing on the possible physiological significance of this mechanism. Application of arachidonic acid (1-100 microM) to either preparation leads to fast (within 30 s) and largely reversible reduction in the uptake rate. When either melittin (0.2-1 microgram/ml), a phospholipase A2 activator, or thimerosal (50-200 microM), which inhibits fatty acid reacylation in phospholipids, is applied to astrocytes, both an enhancement in extracellular free arachidonate and a reduction in glutamate uptake are seen. The two effects display similar dose dependency and time course. In particular, 10% uptake inhibition correlates with 30% elevation in free arachidonate, whereas inhibition greater than or equal to 60% is paralleled by threefold stimulation of arachidonate release. In the presence of albumin (1-10 mg/ml), a free fatty acid-binding protein, inhibition by either melittin, thimerosal, or arachidonic acid is prevented and an enhancement of glutamate uptake above the control levels is observed. Our data show that neuronal and glial glutamate transport systems are highly sensitive to changes in extracellular free arachidonate levels and suggest that uptake inhibition may be a relevant mechanism in the action of arachidonic acid at glutamatergic synapses.
Albumins/pharmacology Animals Arachidonic Acids/analysis/pharmacology/*physiology Astrocytes/drug effects/*metabolism/physiology Biological Transport/drug effects/physiology Cells, Cultured Cerebral Cortex/*cytology/drug effects/ultrastructure Dose-Response Relationship, Drug Extracellular Matrix/*chemistry Glutamates/*pharmacokinetics Male Melitten/pharmacology Rats Synaptosomes/drug effects/*metabolism/physiology Thimerosal/pharmacology Time Factors
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