ABSTRACT
Voltage-gated Na+ channels (Nav ) modulate neuronal excitability, but the roles of the various Nav subtypes in specific neuronal functions such as synaptic transmission are unclear. We investigated expression of the three major brain Nav subtypes (Nav 1.1, Nav 1.2, Nav 1.6) in area CA1 and dentate gyrus of rat hippocampus. Using light and electron microscopy, we found labeling for all three Nav subtypes on dendrites, dendritic spines, and axon terminals, but the proportion of pre- and post-synaptic labeling for each subtype varied within and between subregions of CA1 and dentate gyrus. In the central hilus (CH) of the dentate gyrus, Nav 1.1 immunoreactivity was selectively expressed in presynaptic profiles, while Nav 1.2 and Nav 1.6 were expressed both pre- and post-synaptically. In contrast, in the stratum radiatum (SR) of CA1, Nav 1.1, Nav 1.2, and Nav 1.6 were selectively expressed in postsynaptic profiles. We next compared differences in Nav subtype expression between CH and SR axon terminals and between CH and SR dendrites and spines. Nav 1.1 and Nav 1.2 immunoreactivity was preferentially localized to CH axon terminals compared to SR, and in SR dendrites and spines compared to CH. No differences in Nav 1.6 immunoreactivity were found between axon terminals of CH and SR or between dendrites and spines of CH and SR. All Nav subtypes in both CH and SR were preferentially associated with asymmetric synapses rather than symmetric synapses. These findings indicate selective presynaptic and postsynaptic Nav expression in glutamatergic synapses of CH and SR supporting neurotransmitter release and synaptic plasticity.
Subject(s)
Hippocampus/cytology , Neurons/physiology , Post-Synaptic Density/metabolism , Presynaptic Terminals/metabolism , Protein Subunits/metabolism , Voltage-Gated Sodium Channels/metabolism , Action Potentials/drug effects , Action Potentials/genetics , Animals , Cells, Cultured , Embryo, Mammalian , HEK293 Cells , Humans , Male , NAV1.1 Voltage-Gated Sodium Channel/metabolism , NAV1.1 Voltage-Gated Sodium Channel/ultrastructure , NAV1.2 Voltage-Gated Sodium Channel/metabolism , NAV1.2 Voltage-Gated Sodium Channel/ultrastructure , NAV1.6 Voltage-Gated Sodium Channel/metabolism , NAV1.6 Voltage-Gated Sodium Channel/ultrastructure , Neuronal Plasticity/genetics , Neurons/ultrastructure , Post-Synaptic Density/drug effects , Post-Synaptic Density/ultrastructure , Presynaptic Terminals/drug effects , Presynaptic Terminals/ultrastructure , Protein Subunits/genetics , Rats , Rats, Sprague-Dawley , Voltage-Gated Sodium Channels/genetics , Voltage-Gated Sodium Channels/ultrastructureABSTRACT
With the ultimate goal of detailed structural analysis of mammalian and particularly human voltage-gated sodium channels (VGSCs), we have investigated the relative stability of human and rat VGSCs and compared them with electric eel VGSC. We found that NaV1.3 from rat was the most stable after detergent solubilisation. The order of stability was rNaV1.3>hNaV1.2>hNaV1.1>hNaV1.6>hNaV1.3>hNaV1.4. However, a comparison with the VGSC from Electrophorus electricus, which is most similar to NaV1.4, shows that the eel VGSC is considerably more stable in detergent than the human VGSCs examined. We conclude that current methods of structural analysis, such as single particle electron cryomicroscopy (cryoEM), may be most usefully targeted to eel VGSC or rNaV1.3, but that structural analysis on the full spectrum of VGSCs, by methods that require greater stability such as crystallisation and X-ray crystallography, will require further stabilisation of the channel.
