THE MECHANISM OF PHA-AMINO-3-HYDROXY-5-METHYL-4-ISOXAZOLEPROPIONATE RECEPTOR DESENSITIZATION AFTER REMOVAL OF GLUTAMATE

We have examined responses of AMPA ha-amino-3-hydroxy-5-methyl-4-isoxa zolepropionate) receptors in the chick nucleus magnocellularis to pair s of pulses of glutamate and determined the extent of desensitization and the rate of recovery. Receptors recovered from desensitization wit h a time constant of 16 ms, regardless of the concentration or duratio n of the conditioning pulse. Even with very brief conditioning pulses, evoking submaximal currents, desensitization occurred at a consistent rate after the removal of free ligand. A quantitative kinetic model b ased on these data shows that receptors must desensitize from a closed state. The results provide evidence that very brief exposure to gluta mate, on the time scale of uniquantal synaptic transmission, will resu lt in a significant reduction in sensitivity of postsynaptic receptors .