PICK1 is a Ca2+-sensor for NMDA-induced endocytosis of GluR2-containing AMPARs in hippocampal neurons. (A) Characterisation of NMDA-induced GluR2 internalisation in dissociated hippocampal neurons. Low-density hippocampal cultures, live-labelled with anti-GluR2 antibody, were exposed to drugs as in . After acid stripping of remaining surface antibody, endocytosis of GluR2-containing AMPAR was assayed by immunocytochemistry (visualised by Alexa 568 secondary). Transmission images and internalised GluR2, including a magnified dendritic segment, are shown from representative neurons. Graph shows quantification of internalised AMPAR. Values represent total internalised GluR2 immunoreactivity normalised for cell area (arbitrary units). n=15 cells per condition, ***P<0.0005. (B) Overexpression of WT PICK1 enhances and ΔNT PICK1 occludes NMDA-induced endocytosis of GluR2 in hippocampal neurons. Neurons were infected with virus encoding -IRES-EGFP alone, WT PICK1-IRES-EGFP or ΔNT PICK1-IRES-EGFP, live-labelled with anti-GluR2 antibody, and exposed to 25 μM NMDA for 3 min followed by 12 min incubation after drug washout or 25 μM MK-801 for 15 min. Images of EGFP fluorescence and internalised GluR2, including a magnified dendritic segment, are shown from representative neurons. Graph shows quantification of internalised AMPAR. Values represent total internalised GluR2 immunoreactivity normalised for cell area (arbitrary units). n=15 cells per condition, *P<0.005, **P<0.001, ***P<0.0005.