EXTRACELLULAR ADENOSINE 5'-TRIPHOSPHATE-EVOKED GLUTAMATE RELEASE IN CULTURED HIPPOCAMPAL-NEURONS

Characteristics of extracellular ATP-evoked electrical responses in rat hippocampal neurons were investigated. Extracellular ATP (100-mu-M) induced a rapid depolarization followed by repetitive firings of spikes in these cells under whole-cell current-clamp. In whole-cell voltage-clamp experiments, ATP activated 2 types of inward currents that were inhibited by P2-purinoceptor blocker suramin (300-mu-M). One is a small (about -20 pA) sustained current which is insensitive to tetrodotoxin (TTX), and the other is a large (-100 to - 300 pA) transient current which abolished in the presence of 3-mu-M TTX. The ATP-induced transient current was blocked by 6-cyano-7-nitro-quinoxaline-2,3-dione (CNQX; 30-mu-M), a non-N-methyl-D-aspartate (non-NMDA) receptor antagonist. ATP failed to induce the transient current in the cell which showed the desensitization to quisqualic acid (QA; 10-mu-M), a non NMDA receptor agonist. These findings suggest that ATP directly activates small sustained currents, and indirectly induces the transient currents by evoking glutamate release.