Nav1.8 Sodium Channel (SCN10A)
<table class="infobox infobox-protein">
<tr>
<th class="infobox-header" colspan="2">nav18-protein</th>
</tr>
<tr>
<td class="label">Symbol</td>
<td><strong>NAV18</strong></td>
</tr>
<tr>
<td class="label">Full Name</td>
<td>nav18-protein</td>
</tr>
<tr>
<td class="label">Type</td>
<td>Protein</td>
</tr>
<tr>
<td class="label">UniProt</td>
<td><a href="https://www.uniprot.org/uniprot/?query=NAV18" target="_blank">Search UniProt</a></td>
</tr>
</table>
Introduction
Nav1.8 (encoded by the SCN10A gene) is a voltage-gated sodium channel predominantly expressed in peripheral sensory neurons, where it plays a crucial role in pain signal transmission. As one of the tetrodotoxin-resistant (TTX-R) sodium channels, Nav1.8 exhibits unique electrophysiological properties that enable it to sustain repetitive firing in nociceptive neurons and contribute to the generation and propagation of pain signals. The channel's restricted expression pattern makes it an attractive target for pain therapeutics, with efforts focused on developing selective inhibitors that can treat chronic pain conditions without affecting central nervous system function [chatterjee2012].
Voltage-gated sodium channels are membrane proteins that allow the rapid influx of sodium ions during the upstroke of action potentials. The Nav1.8 channel belongs to the Nav1 family, which includes nine distinct channel subtypes (Nav1.1-Nav1.9), each with unique expression patterns and functional properties. Unlike the TTX-sensitive channels that are blocked by nanomolar concentrations of tetrodotoxin, Nav1.8 and its close relative Nav1.9 are relatively resistant to TTX, requiring micromolar concentrations for block [dibhajj2009].
Overview
Nav1.8 Sodium Channel is a voltage-gated sodium channel specifically expressed in peripheral sensory neurons, particularly in small-diameter C-fiber and Aδ-fiber nociceptors. The channel contributes to the depolarizing phase of action potentials in these neurons and is essential for the transmission of pain signals from the periphery to the central nervous system. Pathological changes in Nav1.8 function are implicated in neuropathic pain, inflammatory pain, and various chronic pain conditions [woolf1999].
The SCN10A gene encodes the Nav1.8 α-subunit, which forms the pore of the channel. This protein consists of four homologous domains (I-IV), each containing six transmembrane segments (S1-S6). The S4 segment serves as the voltage sensor, while the S5-S6 segments form the pore. Associated β-subunits modulate channel trafficking, gating, and expression at the plasma membrane [arimura2004].
Structure and Function
Channel Architecture
Nav1.8 shares the general architecture of voltage-gated sodium channels:
- Four homologous domains (I-IV), each with six transmembrane segments
- Voltage sensor in the S4 segment, containing positively charged arginine residues
- Pore domain formed by S5-S6 loops in each domain
- Cytosolic N- and C-termini that interact with regulatory proteins
The channel has a relatively depolarized voltage-dependence of activation (around -30 mV) compared to many other sodium channels, allowing it to open at more negative membrane potentials. Its slow inactivation kinetics contribute to its role in sustaining repetitive firing [catterall2012].
Tetrodotoxin Resistance
Nav1.8 is one of several "tetrodotoxin-resistant" (TTX-R) sodium channels that require much higher concentrations of TTX for block. This resistance is due to structural features in the pore region that prevent TTX binding. The functional significance of TTX resistance is unclear but may relate to the physiological roles of these channels in sensory neurons that must function in varied and sometimes extreme environments [biernat2014].
Repetitive Firing
Nav1.8 supports high-frequency repetitive firing in nociceptive neurons due to:
- Slow inactivation kinetics: The channel remains open longer than TTX-sensitive channels
- Rapid recovery from inactivation: Allows faster subsequent action potentials
- Depolarized resting potential: Maintains readiness for firing
These properties make Nav1.8 particularly important for the sustained firing required to transmit chronic pain signals [ekberg2006].
Expression and Localization
Peripheral Sensory Neurons
Nav1.8 is expressed almost exclusively in peripheral sensory neurons, particularly:
- Small-diameter C-fiber nociceptors: Unmyelinated fibers that transmit dull, aching pain
- Aδ-fiber nociceptors: Lightly myelinated fibers that transmit sharp, initial pain
- Medium-diameter neurons: Some proprioceptive and mechanoreceptive neurons
Within these neurons, Nav1.8 is localized primarily to the cell body (soma) and along the axons, where it contributes to action potential initiation and propagation [waxman2014].
Dorsal Root Ganglion
The cell bodies of sensory neurons are located in the dorsal root ganglion (DRG) and trigeminal ganglion. Nav1.8 is highly expressed in:
- Nociceptive neurons: Both peptidergic and non-peptidergic
- Thermoreceptive neurons: Sensitive to temperature changes
- Mechanoreceptive neurons: Responding to touch and vibration
The expression pattern is species-dependent and can be altered by nerve injury or inflammation [sheet2008].
Injury-Induced Upregulation
Following nerve injury or inflammation, Nav1.8 expression can increase significantly:
- Surgical nerve injury: Dramatic upregulation in injured and neighboring neurons
- Inflammatory mediators: Cytokines and growth factors increase Nav1.8 transcription
- Neuropathic pain models: Correlates with development of allodynia and hyperalgesia
This upregulation is a key mechanism underlying the transition from acute to chronic pain [abbadie2009].
Role in Pain Processing
Nociceptor Function
Nav1.8 contributes to nociceptor function in several ways:
- Action potential initiation: Reduces threshold for firing
- Repetitive firing: Sustains high-frequency action potential trains
- Conduction velocity: Affects the speed of signal transmission
The channel is particularly important for the sustained, repetitive firing that characterizes chronic pain states [hoyer2008].
Inflammatory Pain
Inflammatory mediators sensitize nociceptors partly through Nav1.8:
- Prostaglandins: Increase Nav1.8 current through PKA activation
- Cytokines: Upregulate Nav1.8 expression via transcription factors
- Growth factors: NGF increases Nav1.8 trafficking to the membrane
This sensitization contributes to hyperalgesia (increased pain from normally painful stimuli) and allodynia (pain from normally non-painful stimuli) [obrien2014].
Neuropathic Pain
Nerve injury produces long-lasting changes in Nav1.8:
- Ectopic firing: Injured neurons develop spontaneous activity
- Central sensitization: Increased spinal cord neuron excitability
- Channel redistribution: Changes in subcellular localization
Nav1.8 is a major contributor to neuropathic pain, and blocking the channel can reverse pain behaviors in animal models [raouf2010].
Visceral Pain
Nav1.8 is expressed in visceral afferents and contributes to:
- Abdominal pain: Irritable bowel syndrome and inflammatory conditions
- Bladder pain: Interstitial cystitis
- Cardiac pain: Ischemic pain signaling
The visceral pain system shows similar Nav1.8-dependent sensitization to somatic pain pathways [leipzig2012].
Channelopathies and Pain Disorders
Inherited Pain Disorders
Mutations in SCN10A are associated with several pain disorders:
- Inherited erythromelalgia: Gain-of-function mutations cause episodic burning pain
- Channelopathy-associated insensitivity to pain: Loss-of-function mutations cause inability to feel pain
- Small-fiber neuropathy: Some mutations cause progressive sensory loss
These human mutations confirm the critical role of Nav1.8 in pain signaling [huang2017].
Migraine
Emerging evidence links Nav1.8 to migraine pathophysiology:
- Trigeminal ganglion expression: Nav1.8 in meningeal pain pathways
- Sensitization: May contribute to allodynia during migraine attacks
- Genetic associations: SCN10A variants linked to migraine susceptibility
Targeting Nav1.8 may provide a novel approach to migraine treatment [fischer2019].
Pediatric Pain
Neonates and infants express Nav1.8 and are vulnerable to:
- Procedural pain: Routine medical procedures cause pain
- Long-term consequences: Early pain exposure alters pain processing
- Channel development: Developmental changes in channel expression
Understanding Nav1.8 in neonates is critical for safe analgesic development [embleton2019].
Therapeutic Targeting
Selective Blockers
Pharmaceutical companies have pursued selective Nav1.8 blockers:
- A-803467: A selective blocker that reduces neuropathic pain in animal models
- PF-04850814: A clinical candidate that showed efficacy in Phase I trials
- CNV1014802: Another clinical-stage Nav1.8 blocker
These compounds aim to provide analgesia without the cardiac and CNS side effects of non-selective sodium channel blockers [yanagisawa2019].
State-Dependent Block
Nav1.8 blockers often exhibit state-dependence:
- Preferentially bind to open or inactivated states
- Provide more effective block during high-frequency firing
- Reduce the chance of affecting normally-functioning neurons
This property is beneficial for treating chronic pain while minimizing side effects [kingwell2020].
Gene Therapy Approaches
Novel approaches to target Nav1.8 include:
- Antisense oligonucleotides: Silence SCN10A expression
- RNAi: Knockdown of Nav1.8 in sensory neurons
- CRISPR editing: Directly correct disease-causing mutations
- Viral vector delivery: Target DRG neurons with therapeutic transgenes
These approaches may provide longer-lasting pain relief than small molecule inhibitors.
Side Effects and Limitations
Cardiovascular Effects
Although Nav1.8 is not expressed in the heart, some blockers have cardiovascular effects:
- Off-target interactions: May affect other sodium channel subtypes
- Proarrhythmic potential: Requires careful cardiac safety testing
- Blood pressure effects: May cause hypotension in some patients
Central Nervous System
Some Nav1.8 blockers can cross the blood-brain barrier:
- Sedation: May cause drowsiness
- CNS side effects: Affects mood and cognition at high doses
- Limited brain penetration: May be advantageous for peripheral selectivity
Efficacy Limitations
Not all pain conditions respond to Nav1.8 blockade:
- Central pain: Less effective for pain originating in the CNS
- Variable response: Individual patients show different efficacy
- Tolerance: May develop with prolonged use
Cross-References
- [SCN10A Gene](/genes/scn10a) - The gene encoding Nav1.8](/genes)
- [Sodium Channels](/proteins/sodium-channels) - Family of voltage-gated sodium channels](/proteins)
- [Pain Pathways](/diseases/chronic-pain) - Neural circuits for pain processing](/circuits)
- [Dorsal Root Ganglion](/cell-types/dorsal-root-ganglion-neurons) - Location of sensory neuron cell bodies](/entities/neurons)
- [Neuropathic Pain](/diseases/neuropathic-pain) - Pain from nerve damage
- [Inflammatory Pain](/diseases/inflammatory-pain) - Pain from tissue damage
External Links
- [UniProt: Q9Y5N9](https://www.uniprot.org/uniprot/Q9Y5N9)
- [PubMed](https://pubmed.ncbi.nlm.nih.gov/) - Biomedical literature
- [IUPHAR Database](https://www.guidetopharmacology.org/) - Receptor pharmacology database
- [GeneCards: SCN10A](https://www.genecards.org/cgi-bin/carddisp.pl?gene=SCN10A)