Spermine (200 µM, pH 6.3) potentiation of WT GluN1/GluN2B and mutant GluN1-E698C/GluN-L795C receptors. Spermine (200 µM, pH 6.5) sensitivity is also shown for WT GluN1/GluN2B receptors and receptors lacking either the GluN1 (GluN1-delNTD/GluN2B WT) or GluN2B (GluN1 WT/GluN2B-delNTD) NTD (data from Mony et al, 2011) 