Distinct gating modes determine the biphasic relaxation of NMDA receptor currents.

Following brief stimulation, macroscopic NMDA receptor currents decay with biphasic kinetics that is believed to reflect glutamate dissociation and receptor desensitization. We found that the fast and slow decay components arise from the simultaneous deactivation of receptor populations that gate with short and long openings, respectively. Because individual receptors switched infrequently between gating modes, the relaxation time course was largely determined by the proportion of channels in each gating mode at the time of stimulation.