Zinc, ifenprodil and pH dose-response curves of wild-type (WT) GluN1/GluN2B receptors and mutant GluN1-E698C/GluN2B-L795C receptors. For comparison, zinc and ifenprodil dose-response curves of GluN1/GluN2B receptors lacking the whole GluN2B NTD (GluN1 WT/GluN2B-delNTD) are also shown (dashed lines; data from Rachline et al, 2005) 