Abstract
Native NMDA receptors (NMDARs) are tetrameric channels formed by two GluN1 and two GluN2 subunits. So far, seven NMDARs subunits have been identified and they can form diheteromeric or triheteromeric NMDARs (more than one type of GluN2 subunit). Extracellular Mg2+ is an important regulator of NMDARs, and particularly the voltage dependence of Mg2+ block is crucial to the roles of NMDARs in synaptic plasticity and the integration of synaptic activity with neuronal activity. Although the Mg2+ block properties of diheteromeric NMDARs are fully investigated, properties of triheteromeric NMDARs are still not clear. Our previous data suggested that dopaminergic neurones expressed triheteromeric GluN1–GluN2B–GluN2D NMDARs. Here, using NMDARs in dopaminergic neurones from postnatal day 7 (P7) rats as a model system, we characterize the voltage-dependent Mg2+ block properties of triheteromeric NMDARs. In control conditions, external Mg2+ significantly inhibits the whole cell NMDA-evoked current in a voltage-dependent manner with IC50 values of 20.9 μm, 53.3 μm and 173 μm at −90 mV, −70 mV and −50 mV, respectively. When the GluN2B-selective antagonist ifenprodil was applied, the Mg2+ sensitivity of the residual NMDA-mediated currents (which is mainly carried by GluN1–GluN2B–GluN2D NMDARs) is reduced to IC50 values of 45.9 μm (−90 mV), 104 μm (−70 mV) and 276 μm (−50 mV), suggesting that triheteromeric GluN1–GluN2B–GluN2D NMDARs have less affinity for external Mg2+ than GluN1–GluN2B receptors. In addition, fitting INMDA–V curves with a trapping Mg2+ block model shows the triheteromeric GluN1–GluN2B–GluN2D NMDARs have weaker voltage-dependent Mg2+ block (δ = 0.56) than GluN1–GluN2B NMDARs. Finally, our concentration jump and single channel recordings suggest that GluN1–GluN2B–GluN2D rather than GluN1–GluN2D NMDARs are present. These data provide information relevant to Mg2+ block characteristics of triheteromeric NMDARs and may help to better understand synaptic plasticity, which is dependent on these triheteromeric NMDARs.
Highlights
NMDA receptors (NMDARs) are tetrameric, glutamate-gated monovalent cation and Ca2+-permeable channels that are expressed by most mammalian neurones (Traynelis et al 2010)
We have reported that NMDARs on dopaminergic neurones of substantia nigra pars compacta (SNc) are composed of diheteromeric GluN1–GluN2B and triheteromeric GluN1–GluN2B–GluN3A and GluN3B (GluN2D) NMDARs (Jones & Gibb, 2005; Brothwell et al 2008; Suarez et al 2010)
As the GluN2B-selective antagonist ifenprodil is more effective at blocking GluN1–GluN2B than GluN1– GluN2B-GluN2A NMDARs (Hatton & Paoletti, 2005), suggesting SNc neurones provide us with an ideal model system to investigate the voltage-dependent Mg2+ block of triheteromeric GluN1–GluN2B–GluN2D NMDARs
Summary
NMDA receptors (NMDARs) are tetrameric, glutamate-gated monovalent cation and Ca2+-permeable channels that are expressed by most mammalian neurones (Traynelis et al 2010). We have reported that NMDARs on dopaminergic neurones of substantia nigra pars compacta (SNc) are composed of diheteromeric GluN1–GluN2B and triheteromeric GluN1–GluN2B–GluN2D NMDARs (Jones & Gibb, 2005; Brothwell et al 2008; Suarez et al 2010). Consistent with this, both GluN2B and GluN2D mRNA and protein are found in early development while no evidence for functional NR2A-containing NMDARs or NR2C protein or mRNA were found at these early postnatal ages (Monyer et al 1994; Dunah et al 1996, 1998). As the GluN2B-selective antagonist ifenprodil is more effective at blocking GluN1–GluN2B than GluN1– GluN2B-GluN2A NMDARs (Hatton & Paoletti, 2005), suggesting SNc neurones provide us with an ideal model system to investigate the voltage-dependent Mg2+ block of triheteromeric GluN1–GluN2B–GluN2D NMDARs
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
