title: CaMKII-mediated phosphorylation of GluN2B regulates recombinant NMDA receptor currents in a chloride-dependent manner.
abstract: Some forms of long-term synaptic plasticity require docking of Ca2+/calmodulin-dependent protein kinase II α (CaMKIIα) to residues 1290-1309 within the intracellular C-terminal tail of the N-methyl-d-aspartate (NMDA) receptor GluN2B subunit. The phosphorylation of Ser1303 within this region destabilizes CaMKII binding. Interestingly, Ser1303 is a substrate for CaMKII itself, as well as PKC and DAPK1, but these kinases have been reported to have contradictory effects on the activity of GluN2B-containing NMDA receptors. Here, we re-assessed the effect of CaMKII on NMDA receptor desensitization in heterologous cells, as measured by the ratio of steady-state to peak currents induced during 3s agonist applications. CaMKIIα co-expression or infusion of constitutively active CaMKII limits the extent of desensitization and preserves current amplitude with repeated stimulation of recombinant GluN1A/GluN2B when examined using low intracellular chloride (Cl-) levels, characteristic of neurons beyond the first postnatal week. In contrast, CaMKIIα enhances the acute rate and extent of desensitization when intracellular Cl-concentrations are high. The apparent dependence of CaMKIIα effects on NMDA receptor desensitization on Cl-concentrations is consistent with the presence of a Ca2+-activated Cl-conductance endogenous to HEK 293 cells, which was confirmed by photolysis of caged-Ca2+. However, Ca2+-activated Cl-conductances are unaffected by CaMKIIα expression, indicating that CaMKII affects agonist-induced whole cell currents via modulation of the NMDA receptor. In support of this idea, CaMKIIα modulation of GluN2B-NMDA receptors is abrogated by the phospho-null mutation of Ser1303 in GluN2B to alanine and occluded by phospho-mimetic mutation of Ser1303 to aspartate regardless of intracellular Cl-concentration. Thus, CaMKII-mediated phosphorylation of GluN2B-containing NMDA receptors reduces desensitization at physiological (low) intracellular Cl-, perhaps serving as a feed-forward mechanism to sustain NMDA-mediated Ca2+entry and continued CaMKII activation during learning and memory.
authors.affiliation: Department of Pharmacology, University of Tennessee Health Science Center, Memphis, TN 38103, United States. Electronic address: stavalin@uthsc.edu.
authors.forename: Steven J
authors.initials: SJ
authors.lastname: Tavalin
authors.affiliation: Department of Molecular Physiology & Biophysics, Brain Institute, and Kennedy Center for Research on Human Development, Vanderbilt University School of Medicine, Nashville, TN, 37232-0615, United States.
authors.forename: Roger J
authors.initials: RJ
authors.lastname: Colbran
mesh_terms: D000200:Action Potentials; D020013:Calcium Signaling; D054732:Calcium-Calmodulin-Dependent Protein Kinase Type 2 / Q000378:metabolism*; D002712:Chlorides / Q000378:metabolism; D057809:HEK293 Cells; D006801:Humans; D010766:Phosphorylation; D011485:Protein Binding; D011499:Protein Processing, Post-Translational; D016194:Receptors, N-Methyl-D-Aspartate / Q000378:metabolism*
chemical_list: D002712:Chlorides; C121001:NR2B NMDA receptor; D016194:Receptors, N-Methyl-D-Aspartate; D054732:Calcium-Calmodulin-Dependent Protein Kinase Type 2
keywords: CaMKII; Calcium; Desensitization; Electrophysiology; NMDA receptor; Phosphorylation; Synaptic plasticity