BLOCK OF GLUTAMATE TRANSPORTERS POTENTIATES POSTSYNAPTIC EXCITATION

We have studied the effects of blockers of glutamate transporters on e xcitatory synaptic transmission to determine whether transporters incr ease the clearance rate of transmitter from the synaptic cleft on the millisecond time scale. The transporter blockers Li+ and THA increased the amplitude, but not the decay time, of spontaneous miniature AMPA receptor EPSCs recorded at 34 degrees C but not 24 degrees C. Evoked A MPA receptor EPSCs were similarly affected by THA. The rapidly dissoci ating AMPA receptor competitive antagonist PDA inhibited evoked AMPA r eceptor EPSCs less in the presence of THA at both temperatures, implyi ng that transporter blockade slows clearance. We suggest that transpor ters speed glutamate clearance mainly by binding glutamate and that AM PA receptors are not saturated by synaptically released glutamate at 3 4 degrees C.