Assessment of receptor channel activity using MK-801 inhibition kinetics. Representative current traces from oocytes expressing either wild-type (WT) or GluN1-E698C/GluN2B-L795C mutant receptors in response to 10 nM MK-801 during agonist application. Responses were scaled to the current amplitude obtained before MK-801 application. Inset, mono-exponential fits of MK-801 wash-in and wash-out. Note the strikingly faster kinetics in mutant receptors, both at the onset and offset of MK-801 