title: Human Nav1.6 Channels Generate Larger Resurgent Currents than Human Nav1.1 Channels, but the Navβ4 Peptide Does Not Protect Either Isoform from Use-Dependent Reduction.
abstract: Voltage-gated sodium channels are responsible for the initiation and propagation of action potentials (APs). Two brain isoforms, Nav1.1 and Nav1.6, have very distinct cellular and subcellular expression. Specifically, Nav1.1 is predominantly expressed in the soma and proximal axon initial segment of fast-spiking GABAergic neurons, while Nav1.6 is found at the distal axon initial segment and nodes of Ranvier of both fast-spiking GABAergic and excitatory neurons. Interestingly, an auxiliary voltage-gated sodium channel subunit, Navβ4, is also enriched in the axon initial segment of fast-spiking GABAergic neurons. The C-terminal tail of Navβ4 is thought to mediate resurgent sodium current, an atypical current that occurs immediately following the action potential and is predicted to enhance excitability. To better understand the contribution of Nav1.1, Nav1.6 and Navβ4 to high frequency firing, we compared the properties of these two channel isoforms in the presence and absence of a peptide corresponding to part of the C-terminal tail of Navβ4. We used whole-cell patch clamp recordings to examine the biophysical properties of these two channel isoforms in HEK293T cells and found several differences between human Nav1.1 and Nav1.6 currents. Nav1.1 channels exhibited slower closed-state inactivation but faster open-state inactivation than Nav1.6 channels. We also observed a greater propensity of Nav1.6 to generate resurgent currents, most likely due to its slower kinetics of open-state inactivation, compared to Nav1.1. These two isoforms also showed differential responses to slow and fast AP waveforms, which were altered by the Navβ4 peptide. Although the Navβ4 peptide substantially increased the rate of recovery from apparent inactivation, Navβ4 peptide did not protect either channel isoform from undergoing use-dependent reduction with 10 Hz step-pulse stimulation or trains of slow or fast AP waveforms. Overall, these two channels have distinct biophysical properties that may differentially contribute to regulating neuronal excitability.
authors.affiliation: Program in Medical Neuroscience, Indiana University School of Medicine, Indianapolis, Indiana, United States of America; Paul and Carole Stark Neurosciences Research Institute, Indiana University School of Medicine, Indianapolis, Indiana, United States of America.
authors.forename: Reesha R
authors.initials: RR
authors.lastname: Patel
authors.affiliation: Department of Pharmacology and Toxicology, Indiana University School of Medicine, Indianapolis, Indiana, United States of America.
authors.forename: Cindy
authors.initials: C
authors.lastname: Barbosa
authors.affiliation: Paul and Carole Stark Neurosciences Research Institute, Indiana University School of Medicine, Indianapolis, Indiana, United States of America; Department of Pharmacology and Toxicology, Indiana University School of Medicine, Indianapolis, Indiana, United States of America.
authors.forename: Yucheng
authors.initials: Y
authors.lastname: Xiao
authors.affiliation: Program in Medical Neuroscience, Indiana University School of Medicine, Indianapolis, Indiana, United States of America; Paul and Carole Stark Neurosciences Research Institute, Indiana University School of Medicine, Indianapolis, Indiana, United States of America; Department of Pharmacology and Toxicology, Indiana University School of Medicine, Indianapolis, Indiana, United States of America.
authors.forename: Theodore R
authors.initials: TR
authors.lastname: Cummins
mesh_terms: D000200:Action Potentials / Q000187:drug effects* / Q000502:physiology; D000595:Amino Acid Sequence; D015870:Gene Expression; D017930:Genes, Reporter; D049452:Green Fluorescent Proteins / Q000235:genetics / Q000378:metabolism; D057809:HEK293 Cells; D006801:Humans; D015640:Ion Channel Gating / Q000187:drug effects; D008954:Models, Biological; D008969:Molecular Sequence Data; D062550:NAV1.1 Voltage-Gated Sodium Channel / Q000235:genetics / Q000378:metabolism*; D062557:NAV1.6 Voltage-Gated Sodium Channel / Q000235:genetics / Q000378:metabolism*; D009474:Neurons / Q000166:cytology / Q000187:drug effects / Q000378:metabolism; D018408:Patch-Clamp Techniques; D010455:Peptides / Q000494:pharmacology*; D010957:Plasmids / Q000737:chemistry / Q000378:metabolism; D017434:Protein Structure, Tertiary; D011994:Recombinant Proteins / Q000235:genetics / Q000378:metabolism; D012964:Sodium / Q000378:metabolism*; D014162:Transfection; D062585:Voltage-Gated Sodium Channel beta-4 Subunit / Q000494:pharmacology
chemical_list: D062550:NAV1.1 Voltage-Gated Sodium Channel; D062557:NAV1.6 Voltage-Gated Sodium Channel; D010455:Peptides; D011994:Recombinant Proteins; C568242:SCN1A protein, human; C477263:SCN4B protein, human; C100681:SCN8A protein, human; D062585:Voltage-Gated Sodium Channel beta-4 Subunit; C485184:enhanced green fluorescent protein; D049452:Green Fluorescent Proteins; D012964:Sodium