PRESYNAPTIC INFLUENCE ON THE TIME-COURSE OF FAST EXCITATORY SYNAPTIC CURRENTS IN CULTURED HIPPOCAMPAL CELLS

Since the lifetime of synaptically released glutamate is thought to be very brief, reflecting diffusion and glutamate uptake, the decay of s ynaptic currents is thought to represent the average elementary lifeti me of a receptor channel bound only once by transmitter molecules, We show here that the decay of evoked non-NMDA synaptic currents can refl ect presynaptic factors, in particular, the prolonged action of transm itter at postsynaptic receptors under conditions of enhanced transmitt er release, We show that diffusion, high-affinity glutamate uptake, an d non-NMDA receptor desensitization are insufficiently rapid to limit the decays of evoked synaptic currents to those of miniature synaptic currents in microcultures of rat hippocampal cells, Our results are co nsistent with recent studies suggesting that during evoked release, mu ltiple glutamate quanta can interact with overlapping postsynaptic rec eptor domains.