ATP stimulates release of excitatory amino acids from cultured Schwann cells

Abstract

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 μM) caused a receptor-mediated increase in release of glutamate and aspartate from Schwann cell cultures. Bath application of adenosine (100 μM) was without effect on release of excitatory amino acids suggesting involvement of P 2 receptors. Suramin, a competitive antagonist at P 2 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 μM 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 μM), an inhibitor of Ca 2+-ATPase of the Ca 2+ 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.