title: Potassium-evoked glutamate release liberates arachidonic acid from cortical neurons.
abstract: Brain cells in situ contain low concentrations of free polyunsaturated fatty acids such as arachidonic acid (AA) that are released following pathological insults. As a large rise in extracellular [K(+)] accompanies cerebral ischemia, we explored whether this was a stimulus for cellular AA release employing a murine mixed cortical cell culture preparation radiolabeled with AA. Elevating the [K(+)](o) from 5 to 52 mm induced a time-dependent increase in [(3)H]AA release, which reached a plateau after 15 min. Removal of [Ca(2+)](o) or addition of CdCl(2) (100 microm) diminished the net high K(+)-induced AA release, as did treatment of the cultures with tetanus toxin (300 ng/ml) to block endogenous neurotransmitter release. Pharmacological antagonism of both ionotropic and metabotropic glutamate receptors completely prevented high K(+)-evoked AA release, indicating that glutamate was the neurotransmitter in question. Addition of exogenous glutamate mimicked precisely the characteristics of AA release that followed increases in [K(+)](o). Finally, glutamate and AA were released solely from neurons as tetanus toxin did not cleave astrocytic synaptobrevin-2, nor was AA released from pure astrocyte cultures using the same stimuli that were effective in mixed cultures. Taken in toto, our data are consistent with the following scenario: high [K(+)](o) depolarizes neurons, causing an influx of Ca(2+) via voltage-gated Ca(2+) channels. This Ca(2+) influx stimulates the release of glutamate into the synaptic cleft, where it activates postsynaptic glutamate receptors. Events likely converge on the activation of a phospholipase A(2) family member and possibly the enzymes diacylglycerol and monoacylglycerol lipases to yield free AA.
authors.affiliation: Department of Neuroscience, University of Connecticut School of Medicine, Farmington 06030-3401, USA.
authors.forename: Ava L
authors.initials: AL
authors.lastname: Taylor
authors.forename: Sandra J
authors.initials: SJ
authors.lastname: Hewett
mesh_terms: D000818:Animals; D016718:Arachidonic Acid / Q000378:metabolism*; D001095:Arachidonic Acids / Q000378:metabolism; D001253:Astrocytes / Q000378:metabolism; D015153:Blotting, Western; D001921:Brain / Q000378:metabolism; D002118:Calcium / Q000378:metabolism; D002478:Cells, Cultured; D018698:Glutamic Acid / Q000378:metabolism*; D008565:Membrane Proteins / Q000378:metabolism; D051379:Mice; D008954:Models, Biological; D009474:Neurons / Q000378:metabolism*; D010741:Phospholipases A / Q000378:metabolism; D011188:Potassium / Q000378:metabolism*; D011485:Protein Binding; D050683:R-SNARE Proteins; D013997:Time Factors
chemical_list: D001095:Arachidonic Acids; D008565:Membrane Proteins; D050683:R-SNARE Proteins; D016718:Arachidonic Acid; D018698:Glutamic Acid; D010741:Phospholipases A; D011188:Potassium; D002118:Calcium