ATP stimulates release of excitatory amino acids from cultured Schwann cells

The release of excitatory amino acids from Schwann cell cultures in the rat was monitored using high-performance liquid chromatography. The basal concentration of glutamate and aspartate was 33 +/- 4 nM (mean +/- S.E.M., n = 12) and 8 +/- 1 nM (mean +/- S.E.M., n = 12), respectively. ATP (100 microM) caused a receptor-mediated increase in release of glutamate and aspartate from Schwann cell cultures. Bath application of adenosine (100 microM) was without effect on release of excitatory amino acids suggesting involvement of P2 receptors. Suramin, a competitive antagonist at P2 receptors, prevented the response to ATP. The release of excitatory amino acids evoked by ATP was not abolished in calcium-depleted saline. Pretreatment of the Schwann cultures with 50 microM 1,2-bis(2-aminophenoxy)ethane-N,N,N'N'-tetracetic acid-acetoxymethyl ester (BAPTA-AM) abolished the effect of ATP. ATP-evoked release of glutamate from cultured Schwann cells was significantly reduced by thapsigargin (1 microM), an inhibitor of Ca(2+)-ATPase of the Ca2+ pump of internal stores. U73122, a selective inhibitor of receptor-coupled phospholipase C-dependent processes, abolished stimulatory effect of ATP suggesting that ATP's action is mediated through an inositol 1,4,5-triphosphate-sensitive calcium store. The action of ATP was not blocked by L-trans-pyrrolidine-2,4-dicarboxylate, an inhibitor of the electrogenic glutamate transporter, nor was it blocked in Na(+)-free medium, and glutamate release was not stimulated by a depolarizing stimulus, suggesting that ATP-evoked release of glutamate from Schwann cells is not due to the reversal of the glutamate uptake. An anion transport blocker, furosemide, reduced ATP-induced glutamate release. These results suggest that ATP-stimulated glutamate and aspartate release from Schwann cells may be through a calcium-dependent furosemide-sensitive mechanism.