Modulation of the glutamate-evoked release of arachidonic acid from mouse cortical neurons: involvement of a pH-sensitive membrane phospholipase A2.
Excitatory synaptic transmission is associated with changes in both extracellular and intracellular pH. Using mouse cortical neurons in primary cultures, we studied the sensitivity of glutamate-evoked release of 3H-arachidonic acid (3H-AA) to changes in extracellular pH (pHo) and related intracellular pH (pHi). As pHo was shifted from 7.2 to 7.8, the glutamate-evoked release of 3H-AA was enhanced by approximately threefold. The effect of alkaline pHo on the glutamate response was rapid, becoming significant within 2 min. 3H-AA release, evoked by both NMDA and kainate, was also enhanced by pHo alkalinization. NMDA- and kainate-induced increase in free intracellular Ca2+ was unaffected by changing pHo from 7.2 to 7.8, indicating that the receptor-induced Ca2+ influx is not responsible for the pHo sensitivity of the glutamate-evoked release of 3H-AA. Alkalinization of pHi obtained by incubating neurons in the presence of HCO3- or NH4 enhanced the glutamate-evoked release of 3H-AA, while pHi acidification obtained by blockade of Na+/H+ and Cl-/HCO3- exchangers decreased the glutamate response. Membrane-bound phospholipase A2 (mPLA2) activity was stimulated by Ca2+ in a pH-dependent manner, increasing its activity as pH was shifted from 7.2 to 7.8. This pH profile corresponds to the pH profile of the glutamate-, NMDA- and kainate-evoked release of 3H-AA. Taken together, these results indicate that the glutamate-evoked release of 3H-AA may be mediated by the pH-sensitive mPLA2. Since excitatory neurotransmission mediated by glutamate results in both pHo and pHi changes and since AA enhances glutamatergic neurotransmission at both pre- and postsynaptic levels, the data reported here reveals a possible molecular mechanism whereby glutamate can modulate its own signalling efficacy in a pH-dependent manner by regulating the release of AA.
Stella
N
N
Laboratoire de Recherches Neurologiques, Faculte de Medecine, Université de Lausanne, Switzerland.
Pellerin
L
L
Magistretti
P J
PJ
D017878:4,4'-Diisothiocyanostilbene-2,2'-Disulfonic Acid / Q000494:pharmacology; D018750:6-Cyano-7-nitroquinoxaline-2,3-dione / Q000494:pharmacology; D000584:Amiloride / Q000494:pharmacology; D000643:Ammonium Chloride / Q000494:pharmacology; D000818:Animals; D016718:Arachidonic Acid / Q000378:metabolism*; D002118:Calcium / Q000378:metabolism; D002462:Cell Membrane / Q000201:enzymology; D002470:Cell Survival; D002478:Cells, Cultured; D002540:Cerebral Cortex / Q000166:cytology / Q000378:metabolism*; D016291:Dizocilpine Maleate / Q000494:pharmacology; D004622:Embryo, Mammalian; D005260:Female; D018698:Glutamic Acid / Q000494:pharmacology*; D006246:Harmaline / Q000494:pharmacology; D006863:Hydrogen-Ion Concentration; D007150:Immunohistochemistry; D007608:Kainic Acid / Q000494:pharmacology; D007700:Kinetics; D007736:Kynurenic Acid / Q000494:pharmacology; D051379:Mice; D016202:N-Methylaspartate / Q000494:pharmacology; D009474:Neurons / Q000166:cytology / Q000187:drug effects / Q000378:metabolism*; D010741:Phospholipases A / Q000378:metabolism*; D054467:Phospholipases A2; D011247:Pregnancy; D013997:Time Factors; D014316:Tritium
D000643:Ammonium Chloride; D014316:Tritium; D016718:Arachidonic Acid; D018698:Glutamic Acid; D016202:N-Methylaspartate; D016291:Dizocilpine Maleate; D018750:6-Cyano-7-nitroquinoxaline-2,3-dione; D000584:Amiloride; D006246:Harmaline; D010741:Phospholipases A; D054467:Phospholipases A2; D007736:Kynurenic Acid; D017878:4,4'-Diisothiocyanostilbene-2,2'-Disulfonic Acid; D007608:Kainic Acid; D002118:Calcium