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Original Article

Subunit Dependencies of N-Methyl-D-aspartate (NMDA) Receptor-Induced -Amino-3-hydroxy-5-methyl-4-isoxazolepropionic Acid (AMPA) Receptor Internalization

Laboratory for Molecular Pharmacology, Department of Pharmacology, University College London, London, United Kingdom (C.M.T., A.T., G.F.R., C.G.S., R.S.); Novartis Institutes for Biomedical Research, Novartis Pharma AG, Basel, Switzerland (Y.P.A.); and Department of Biological Sciences, The Open University, Milton Keynes, United Kingdom (M.G.S.)

Abstract

N-Methyl-D-aspartate (NMDA) receptor (NMDAR) activity regulates the net number of -amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) receptors (AMPAR) at the cell surface by modulating the balance between AMPAR membrane insertion and endocytosis. In this study, we addressed the role of NMDAR subtypes and of NMDAR-mediated Ca²⁺ influx in the NMDAR-induced endocytosis of GluR2-containing AMPARs in primary murine hippocampal neurons. We found that NMDAR activation enhanced the endocytosis of AMPARs containing the GluR2 splice variants with short, but not long, cytoplasmic tails. NMDA-induced GluR2 endocytosis was completely inhibited by pharmacological block of NR2B-containing NMDARs. In turn, preferential block of NR2A-containing NMDARs did not affect NMDA-induced AMPAR endocytosis, indicating that AMPAR internalization is controlled by a restricted set of NMDARs. The NMDA-induced GluR2 internalization was also observed in the absence of extracellular Na⁺ ions, suggesting that membrane depolarization is not a prerequisite for this effect. Furthermore, the activation of Ca²⁺-impermeable NMDARs containing the mutant NR1(N598R) subunit failed to enhance AMPAR endocytosis, indicating a requirement of Ca²⁺ influx directly through the NMDAR channels. In summary, our findings suggest that the NMDAR-induced selective internalization of short C-terminal GluR2-containing AMPARs requires a Ca²⁺ signal that originates from NMDAR channels and is processed in an NMDAR subtype-restricted manner.

Address correspondence to: Ralf Schoepfer, Laboratory for Molecular Pharmacology, Department of Pharmacology, UCL, Gower Street, London WC1E 6BT, UK. E-mail: r.schoepfer{at}ucl.ac.uk

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