Enhanced trafficking of an inherited erythromelalgia Na1.7 mutant channel at a physiological temperature.

Gain-of-function mutations which enhance activation of Na1.7, a widely expressed sodium channel in nociceptors, cause human pain disorders including inherited erythromelalgia (IEM). IEM is characterized by attacks of burning pain in distal extremities triggered by warmth, with cooling of affected limbs providing temporary relief.

High-throughput multiplex voltage-clamp/current-clamp evaluation of acutely isolated neurons.

The patch-clamp technique remains the gold-standard for the investigation of excitable cells. However, the manual implementation of this technique is slow and low throughput. While recently developed high-throughput robotic patch-clamp methods have proven valuable for drug screening, they have predominantly focused on investigating receptors and channels overexpressed in heterologous cell lines.

Sculpting excitable membranes: voltage-gated ion channel delivery and distribution.

The polarized and domain-specific distribution of membrane ion channels is essential for neuronal homeostasis, but delivery of these proteins to distal neuronal compartments (such as the axonal ends of peripheral sensory neurons) presents a logistical challenge. Recent developments have enabled the real-time imaging of single protein trafficking and the investigation of the life cycle of ion channels across neuronal compartments. These studies have revealed a highly regulated process involving post-translational modifications, vesicular sorting, motor protein-driven transport and targeted membrane insertion.

Targeted ubiquitination of Na 1.8 reduces sensory neuronal excitability.

Chronic pain and addiction are a significant global health challenge. Voltage-gated sodium channel Na 1.8, a pivotal driver of pain signaling, is a clinically validated target for the development of novel, non-addictive pain therapeutics.

The evolution of patch-clamp electrophysiology: Robotic, multiplex, and dynamic.

The patch-clamp technique has been the gold standard for analysis of excitable cells. Since its development in the 1980s, it has contributed immensely to our understanding of neurons, muscle cells, and cardiomyocytes and the ion channels and receptors that reside within them. This technique, predicated on Ohm's law, enables precise measurement of macroscopic excitability patterns and assessment of ionic and gating conductance, even to the single channel level.

Voltage-gated sodium channels in excitable cells as drug targets.

Excitable cells - including neurons, muscle cells and cardiac myocytes - are unique in expressing high densities of voltage-gated sodium (Na) channels. This molecular adaptation enables these cells to produce action potentials, and is essential to their function. With the advent of the molecular revolution, the concept of 'the' sodium channel has been supplanted by understanding that excitable cells in mammals can express any of nine different forms of sodium channels (Na1.

TRPM8 Mutations Associated With Persistent Pain After Surgical Injury of Corneal Trigeminal Axons.

Background And Objectives: Despite extensive efforts, the mechanisms underlying pain after axonal injury remain incompletely understood. Pain following corneal refractive surgery offers a valuable human model for investigating trigeminal axonal injury because laser-assisted in situ keratomileusis (LASIK) severs axons of trigeminal ganglion neurons innervating the cornea. While the majority of patients are pain-free shortly after surgery, a minority endure persistent postoperative ocular pain.

Disordered but effective: short linear motifs as gene therapy targets for hyperexcitability disorders.

Multiple approaches have targeted voltage-gated sodium (Nav) channels for analgesia. In this issue of the JCI, Shin et al. identified a peptide aptamer, NaViPA1, carrying a short polybasic motif flanked by serine residues in a structurally disordered region of loop 1 in tetrodotoxin-sensitive (TTX-S) but not tetrodotoxin-resistant (TTX-R) channels.

Real-time imaging of axonal membrane protein life cycles.

The construction of neuronal membranes is a dynamic process involving the biogenesis, vesicular packaging, transport, insertion and recycling of membrane proteins. Optical imaging is well suited for the study of protein spatial organization and transport. However, various shortcomings of existing imaging techniques have prevented the study of specific types of proteins and cellular processes.

Nav1.8 in small dorsal root ganglion neurons contributes to vincristine-induced mechanical allodynia.

Vincristine-induced peripheral neuropathy is a common side effect of vincristine treatment, which is accompanied by pain and can be dose-limiting. The molecular mechanisms that underlie vincristine-induced pain are not well understood. We have established an animal model to investigate pathophysiological mechanisms of vincristine-induced pain.

Functionally-selective inhibition of threshold sodium currents and excitability in dorsal root ganglion neurons by cannabinol.

Cannabinol (CBN), an incompletely understood metabolite for ∆9-tetrahydrocannabinol, has been suggested as an analgesic. CBN interacts with endocannabinoid (CB) receptors, but is also reported to interact with non-CB targets, including various ion channels. We assessed CBN effects on voltage-dependent sodium (Nav) channels expressed heterologously and in native dorsal root ganglion (DRG) neurons.

Compartment-specific regulation of Na1.7 in sensory neurons after acute exposure to TNF-α.

Tumor necrosis factor α (TNF-α) is a major pro-inflammatory cytokine, important in many diseases, that sensitizes nociceptors through its action on a variety of ion channels, including voltage-gated sodium (Na) channels. We show here that TNF-α acutely upregulates sensory neuron excitability and current density of threshold channel Na1.7.

Sodium currents in naïve mouse dorsal root ganglion neurons: No major differences between sexes.

Sexual dimorphism has been reported in multiple pre-clinical and clinical studies on pain. Previous investigations have suggested that in at least some states, rodent dorsal root ganglion (DRG) neurons display differential sex-dependent regulation and expression patterns of various proteins involved in the pain pathway. Our goal in this study was to determine whether sexual dimorphism in the biophysical properties of voltage-gated sodium (Nav) currents contributes to these observations in rodents.

Na1.7: A central role in pain.

Loss of function of sodium channel Na1.7 produces pain insensitivity. In this issue, Deng et al.

Pain-causing stinging nettle toxins target TMEM233 to modulate Na1.7 function.

Voltage-gated sodium (Na) channels are critical regulators of neuronal excitability and are targeted by many toxins that directly interact with the pore-forming α subunit, typically via extracellular loops of the voltage-sensing domains, or residues forming part of the pore domain. Excelsatoxin A (ExTxA), a pain-causing knottin peptide from the Australian stinging tree Dendrocnide excelsa, is the first reported plant-derived Na channel modulating peptide toxin. Here we show that TMEM233, a member of the dispanin family of transmembrane proteins expressed in sensory neurons, is essential for pharmacological activity of ExTxA at Na channels, and that co-expression of TMEM233 modulates the gating properties of Na1.

Conserved but not critical: Trafficking and function of Na1.7 are independent of highly conserved polybasic motifs.

Non-addictive treatment of chronic pain represents a major unmet clinical need. Peripheral voltage-gated sodium (Na) channels are an attractive target for pain therapy because they initiate and propagate action potentials in primary afferents that detect and transduce noxious stimuli. Na1.

Na1.7 gain-of-function mutation I228M triggers age-dependent nociceptive insensitivity and C-LTMR dysregulation.

Gain-of-function mutations in Scn9a, which encodes the peripheral sensory neuron-enriched voltage-gated sodium channel Na1.7, cause paroxysmal extreme pain disorder (PEPD), inherited erythromelalgia (IEM), and small fiber neuropathy (SFN). Conversely, loss-of-function mutations in the gene are linked to congenital insensitivity to pain (CIP).

Inflammation differentially controls transport of depolarizing Nav versus hyperpolarizing Kv channels to drive rat nociceptor activity.

Inflammation causes pain by shifting the balance of ionic currents in nociceptors toward depolarization, leading to hyperexcitability. The ensemble of ion channels within the plasma membrane is regulated by processes including biogenesis, transport, and degradation. Thus, alterations in ion channel trafficking may influence excitability.

Paclitaxel effects on axonal localization and vesicular trafficking of Na1.8.

Patients treated with paclitaxel (PTX) or other antineoplastic agents can experience chemotherapy-induced peripheral neuropathy (CIPN), a debilitating side effect characterized by numbness and pain. PTX interferes with microtubule-based transport, which inhibits tumor growth cell cycle arrest but can also affect other cellular functions including trafficking of ion channels critical to transduction of stimuli by sensory neurons of the dorsal root ganglia (DRG). We examined the effects of PTX on voltage-gated sodium channel Na1.

High-throughput combined voltage-clamp/current-clamp analysis of freshly isolated neurons.

The patch-clamp technique is the gold-standard methodology for analysis of excitable cells. However, throughput of manual patch-clamp is slow, and high-throughput robotic patch-clamp, while helpful for applications like drug screening, has been primarily used to study channels and receptors expressed in heterologous systems. We introduce an approach for automated high-throughput patch-clamping that enhances analysis of excitable cells at the channel and cellular levels.

Nav1.7 P610T mutation in two siblings with persistent ocular pain after corneal axon transection: impaired slow inactivation and hyperexcitable trigeminal neurons.

Despite extensive study, the mechanisms underlying pain after axonal injury remain incompletely understood. Pain after corneal refractive surgery provides a model, in humans, of the effect of injury to trigeminal afferent nerves. Axons of trigeminal ganglion neurons that innervate the cornea are transected by laser-assisted in situ keratomileusis (LASIK).

The fates of internalized Na1.7 channels in sensory neurons: Retrograde cotransport with other ion channels, axon-specific recycling, and degradation.

Neuronal function relies on the maintenance of appropriate levels of various ion channels at the cell membrane, which is accomplished by balancing secretory, degradative, and recycling pathways. Neuronal function further depends on membrane specialization through polarized distribution of specific proteins to distinct neuronal compartments such as axons. Voltage-gated sodium channel Na1.