High Probability Opening of NMDA Receptor Channels by L-Glutamate

Synaptic plasticity can be triggered by calcium flux into neurons through synaptically activated N-methyl-D-aspartate (NMDA) receptor channels. The amplitude and time course of the resulting intracellular calcium transient depend on the number of open NMDA receptor channels and the kinetics of their activation. Short applications of L-glutamate to outside-out patches from hippocampal neurons in the presence and absence of MK-801 revealed that about 30 percent of L-glutamate-bound channels are open at the peak of the current. This high probability of opening suggests that very few channels are required to guarantee a large, localized postsynaptic calcium transient.