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The sodium bicarbonate cotransporter NBCn1 is an electroneutral transporter with a channel activity that conducts Na+ in a HCO3--independent manner. This channel activity was suggested to functionally affect other membrane proteins which permeate Na+ influx. We previously reported that NBCn1 is associated with the NMDA receptors (NMDARs) at the molecular and physiological levels. In this study, we examined whether NBCn1 channel activity affects NMDAR currents and whether this effect involves the interaction between the two proteins. NBCn1 and the NMDAR subunits GluN1A/GluN2A were expressed in Xenopus oocytes, and glutamate currents produced by the receptors were measured using two-electrode voltage clamp. In the absence of CO2/HCO3-, NBCn1 channel activity decreased glutamate currents mediated by GluN1A/GluN2A. NBCn1 also decreased the slope of the current-voltage relationships for the glutamate current. Similar effects on the glutamate current were observed with and without PSD95, which can cluster NBCn1 and NMDARs. The channel activity was also observed in the presence of CO2/HCO3-. We conclude that NBCn1 channel activity decreases NMDAR function. Given that NBCn1 knockout mice develop a downregulation of NMDARs, our results are unexpected and suggest that NBCn1 has dual effects on NMDARs. It stabilizes NMDAR expression but decreases receptor function by its Na+ channel activity. The dual effects may play an important role in fine-tuning the regulation of NMDARs in the brain.
Figure 1. NBCn1 channel activity. (A) I–V relationships in oocytes expressing NBCn1 or water-injected control oocytes. Oocytes were subjected to step-voltage commands from –120 to +60 mV (20 mV steps) in CO2/HCO3−-free ND96 solution (n = 5–7/group). The increased slope of the I–V plot is a hallmark for NBCn1 channel activity. (B) INBCn1–V relationship of NBCn1 channel activity. The plot was obtained from the difference between the I–V plots in the presence and absence of bath Na+. (C) Resting membrane potentials (Vm). Vm was measured 48–72 h after cRNA injection (n = 5 controls and 16 NBCn1). ** p < 0.01, Student t-test.
Figure 2. NBCn1 channel activity decreases IGlu produced by GluN1·N2. (A) Representative IGlu produced by GluN1·N2. IGlu was measured with an application of 100 µM glutamate (10 µM glycine, no Mg2+). Recording was performed in CO2/HCO3−-free ND96 solution containing 96 mM NaCl (holding potential of –40 mV). (B–D) Representative IGlu produced by GluN1·N2/NBCn1. A fixed amount of GluN1·N2 was coexpressed with 1, 5, or 10 ng of NBCn1. (E) Control. (F) Mean IGlu. Data were obtained from 4–5 oocytes/group. * p < 0.05, ** p < 0.01 compared to GluN1·N2 alone, one-way ANOVA with Dunnett post-test. (G) and (H) I–V relationships of glutamate-evoked responses by GluN1·N2 (n = 6; (G)) and GluN1·N2/NBCn1 (n = 5; (H)). (I) IGlu–V relationships. IGlu is the mean difference before and after glutamate application in (G) and (H). NBCn1 alone served as a control (n = 4).
Figure 3. PSD95 increases IGlu produced by GluN1·N2. (A) I–V relationships of glutamate-evoked responses by GluN1·N2 (n = 3). (B) I–V relationships of glutamate-evoked responses by GluN1·N2/PSD95 (n = 5). (C) IGlu–V relationships. IGlu is the mean difference before and after glutamate application in (A) and (B).
Figure 4. PSD95 has negligible effect on IGlu in the presence of NBCn1. (A) I–V relationships of glutamate-evoked responses by GluN1·N2/NBCn1 (n = 11). (B) I–V relationships of glutamate-evoked responses by GluN1·N2/PSD95/NBCn1 (n = 7). (C) IGlu–V relationships. IGlu is the mean difference before and after glutamate application in (A,B).
Figure 5. The IGlu decrease by NBCn1 channel activity is independent of CO2/HCO3−. (A,B) Representative IGlu produced by GluN1·N2/PSD95 (A) and GluN1·N2/PSD95/NBCn1 (B). IGlu was measured in ND96 solution and 10 min after applying a solution equilibrated with 10% CO2, 50 mM HCO3− at constant pH 7.4. Except when glutamate was applied, Na+-free CO2/HCO3− solution was applied to minimize pHi change by cotransport activity. (C) Mean IGlu produced by GluN1·N2/PSD95 (n = 4; (C)) and GluN1·N2/PSD95/NBCn1 (n = 6; (D)). (E) Effects of NBCn1 on IGlu in the absence and presence of CO2/HCO3−. Data were presented as percent change relative to IGlu by GluN1·N2/PSD95. ** p < 0.01.
Aalkjaer,
Cation-coupled bicarbonate transporters.
2014,
Pubmed Boron,
Evaluating the role of carbonic anhydrases in the transport of HCO3--related species.
2010,
Pubmed Choi,
An electroneutral sodium/bicarbonate cotransporter NBCn1 and associated sodium channel.
2000,
Pubmed
,
Xenbase Choi,
SLC4A transporters.
2012,
Pubmed Cooper,
Molecular and functional characterization of the electroneutral Na/HCO3 cotransporter NBCn1 in rat hippocampal neurons.
2005,
Pubmed
,
Xenbase Cooper,
Sodium/bicarbonate cotransporter NBCn1/slc4a7 increases cytotoxicity in magnesium depletion in primary cultures of hippocampal neurons.
2009,
Pubmed Cougnon,
Effect of reactive oxygen species on NH4+ permeation in Xenopus laevis oocytes.
2002,
Pubmed
,
Xenbase de Lera Ruiz,
Voltage-Gated Sodium Channels: Structure, Function, Pharmacology, and Clinical Indications.
2015,
Pubmed Dingledine,
The glutamate receptor ion channels.
1999,
Pubmed George,
Bidirectional influence of sodium channel activation on NMDA receptor-dependent cerebrocortical neuron structural plasticity.
2012,
Pubmed Grichtchenko,
Cloning, characterization, and chromosomal mapping of a human electroneutral Na(+)-driven Cl-HCO3 exchanger.
2001,
Pubmed
,
Xenbase Kim,
PDZ domain proteins of synapses.
2004,
Pubmed Ko,
A molecular mechanism for aberrant CFTR-dependent HCO(3)(-) transport in cystic fibrosis.
2002,
Pubmed Lee,
PSD-95 interacts with NBCn1 and enhances channel-like activity without affecting Na/HCO(3) cotransport.
2012,
Pubmed
,
Xenbase Lee,
Systematic family-wide analysis of sodium bicarbonate cotransporter NBCn1/SLC4A7 interactions with PDZ scaffold proteins.
2014,
Pubmed
,
Xenbase Lee,
Sodium-bicarbonate cotransporter NBCn1/Slc4a7 inhibits NH4Cl-mediated inward current in Xenopus oocytes.
2011,
Pubmed
,
Xenbase Lin,
Postsynaptic density protein-95 regulates NMDA channel gating and surface expression.
2004,
Pubmed
,
Xenbase Low,
Molecular determinants of coordinated proton and zinc inhibition of N-methyl-D-aspartate NR1/NR2A receptors.
2000,
Pubmed
,
Xenbase Park,
Neuronal expression of sodium/bicarbonate cotransporter NBCn1 (SLC4A7) and its response to chronic metabolic acidosis.
2010,
Pubmed Park,
Deletion of the Na/HCO3 Transporter NBCn1 Protects Hippocampal Neurons from NMDA-induced Seizures and Neurotoxicity in Mice.
2019,
Pubmed Park,
Alternative transcription of sodium/bicarbonate transporter SLC4A7 gene enhanced by single nucleotide polymorphisms.
2017,
Pubmed
,
Xenbase Parker,
Characterization of human SLC4A10 as an electroneutral Na/HCO3 cotransporter (NBCn2) with Cl- self-exchange activity.
2008,
Pubmed
,
Xenbase Parker,
The divergence, actions, roles, and relatives of sodium-coupled bicarbonate transporters.
2013,
Pubmed Ren,
Sodium leak channels in neuronal excitability and rhythmic behaviors.
2011,
Pubmed Richter,
The recruitment of membrane-bound mRNAs for translation in microinjected Xenopus oocytes.
1983,
Pubmed
,
Xenbase Romero,
Cloning and characterization of a Na+-driven anion exchanger (NDAE1). A new bicarbonate transporter.
2000,
Pubmed
,
Xenbase Romero,
The SLC4 family of bicarbonate (HCO₃⁻) transporters.
2013,
Pubmed Salter,
Src kinases: a hub for NMDA receptor regulation.
2004,
Pubmed Sato,
Purification and characterization of a Src-related p57 protein-tyrosine kinase from Xenopus oocytes. Isolation of an inactive form of the enzyme and its activation and translocation upon fertilization.
1996,
Pubmed
,
Xenbase Schank,
Increased Alcohol Consumption in Mice Lacking Sodium Bicarbonate Transporter NBCn1.
2020,
Pubmed Shcheynikov,
The Slc26a4 transporter functions as an electroneutral Cl-/I-/HCO3- exchanger: role of Slc26a4 and Slc26a6 in I- and HCO3- secretion and in regulation of CFTR in the parotid duct.
2008,
Pubmed
,
Xenbase Soleimani,
Ionic mechanism of Na+-HCO3- cotransport in rabbit renal basolateral membrane vesicles.
1989,
Pubmed Spanagel,
Alcoholism: a systems approach from molecular physiology to addictive behavior.
2009,
Pubmed Sugrue,
Immunocytochemical localization of the neuron-specific form of the c-src gene product, pp60c-src(+), in rat brain.
1990,
Pubmed Tauskela,
Protection of cortical neurons against oxygen-glucose deprivation and N-methyl-D-aspartate by DIDS and SITS.
2003,
Pubmed Traynelis,
Glutamate receptor ion channels: structure, regulation, and function.
2010,
Pubmed Wang,
Role of Glutamate and NMDA Receptors in Alzheimer's Disease.
2017,
Pubmed Yu,
Overview of the voltage-gated sodium channel family.
2003,
Pubmed Yu,
The Role of Intracellular Sodium in the Regulation of NMDA-Receptor-Mediated Channel Activity and Toxicity.
2006,
Pubmed Yu,
Gain control of NMDA-receptor currents by intracellular sodium.
1998,
Pubmed Zhang,
Structural Basis of the Proton Sensitivity of Human GluN1-GluN2A NMDA Receptors.
2018,
Pubmed
,
Xenbase Zhekova,
Identification of multiple substrate binding sites in SLC4 transporters in the outward-facing conformation: Insights into the transport mechanism.
2021,
Pubmed
