Damage-sensing nociceptors in the skin provide an indispensable protective function thanks to their specialized ability to detect and transmit hot temperatures that would block or inflict irreversible damage in other mammalian neurons. Here we show that the exceptional capacity of skin C-fiber nociceptors to encode noxiously hot temperatures depends on two tetrodotoxin (TTX)-resistant sodium channel α-subunits: NaV1.8 and NaV1.9. We demonstrate that NaV1.9, which is commonly considered an amplifier of subthreshold depolarizations at 20°C, undergoes a large gain of function when temperatures rise to the pain threshold. We also show that this gain of function renders NaV1.9 capable of generating action potentials with a clear inflection point and positive overshoot. In the skin, heat-resistant nociceptors appear as two distinct types with unique and possibly specialized features: one is blocked by TTX and relies on NaV1.9, and the second type is insensitive to TTX and composed of both NaV1.8 and NaV1.9. Independent of rapidly gated TTX-sensitive NaV channels that form the action potential at pain threshold, NaV1.8 is required in all heat-resistant nociceptors to encode temperatures higher than ∼46°C, whereas NaV1.9 is crucial for shaping the action potential upstroke and keeping the NaV1.8 voltage threshold within reach.

• MeSH
• akční potenciály MeSH
• buněčné linie MeSH
• kůže MeSH
• metoda terčíkového zámku MeSH
• molekulární evoluce MeSH
• myši inbrední C57BL MeSH
• napětově řízený sodíkový kanál typ 10 metabolismus   MeSH
• napětově řízený sodíkový kanál typ 11 metabolismus   MeSH
• nociceptory metabolismus   MeSH
• práh bolesti MeSH
• techniky in vitro MeSH
• vysoká teplota * MeSH
• zvířata MeSH
• Check Tag
• zvířata MeSH
• Publikační typ
• časopisecké články MeSH
• práce podpořená grantem MeSH
• Názvy látek
• napětově řízený sodíkový kanál typ 10 MeSH
• napětově řízený sodíkový kanál typ 11 MeSH
• Scn10a protein, mouse MeSH Prohlížeč
• Scn11a protein, mouse MeSH Prohlížeč

Ciguatoxins (CTXs) are marine toxins that cause ciguatera fish poisoning, a debilitating disease dominated by sensory and neurological disturbances that include cold allodynia and various painful symptoms as well as long-lasting pruritus. Although CTXs are known as the most potent mammalian sodium channel activator toxins, the etiology of many of its neurosensory symptoms remains unresolved. We recently described that local application of 1 nM Pacific Ciguatoxin-1 (P-CTX-1) into the skin of human subjects induces a long-lasting, painful axon reflex flare and that CTXs are particularly effective in releasing calcitonin-gene related peptide (CGRP) from nerve terminals. In this study, we used mouse and rat skin preparations and enzyme-linked immunosorbent assays (ELISA) to study the molecular mechanism by which P-CTX-1 induces CGRP release. We show that P-CTX-1 induces CGRP release more effectively in mouse as compared to rat skin, exhibiting EC50 concentrations in the low nanomolar range. P-CTX-1-induced CGRP release from skin is dependent on extracellular calcium and sodium, but independent from the activation of various thermosensory transient receptor potential (TRP) ion channels. In contrast, lidocaine and tetrodotoxin (TTX) reduce CGRP release by 53-75%, with the remaining fraction involving L-type and T-type voltage-gated calcium channels (VGCC). Using transgenic mice, we revealed that the TTX-resistant voltage-gated sodium channel (VGSC) NaV1.9, but not NaV1.8 or NaV1.7 alone and the combined activation of the TTX-sensitive VGSC subtypes NaV1.7 and NaV1.1 carry the largest part of the P-CTX-1-caused CGRP release of 42% and 34%, respectively. Given the contribution of CGRP to nociceptive and itch sensing pathways, our findings contribute to a better understanding of sensory symptoms of acute and chronic ciguatera that may help in the identification of potential therapeutics.

• Klíčová slova
• P-CTX-1, TRPA1, TRPC5, TRPM8, TTX, calcitonin-gene related peptide, ciguatera, neurogenic inflammation, neuropathic pain, tetrodotoxin, voltage-gated calcium channels,
• MeSH
• ciguatera metabolismus   MeSH
• ciguatoxiny chemie   farmakologie   MeSH
• ELISA MeSH
• hyperalgezie chemicky indukované   MeSH
• krysa rodu Rattus MeSH
• lidé MeSH
• lidokain farmakologie   MeSH
• membránové potenciály účinky léků   MeSH
• mořské toxiny farmakologie   MeSH
• myši transgenní MeSH
• myši MeSH
• napětím řízený sodíkový kanál, typ 1 účinky léků   MeSH
• napětově řízený sodíkový kanál typ 11 účinky léků   MeSH
• napěťově řízený sodíkový kanál, typ 9 účinky léků   MeSH
• peptid spojený s genem pro kalcitonin účinky léků   MeSH
• receptory peptidu se vztahem ke genu kalcitoninu účinky léků   MeSH
• tetrodotoxin farmakologie   MeSH
• vápník metabolismus   MeSH
• zvířata MeSH
• Check Tag
• krysa rodu Rattus MeSH
• lidé MeSH
• mužské pohlaví MeSH
• myši MeSH
• zvířata MeSH
• Publikační typ
• časopisecké články MeSH
• Názvy látek
• CALCA protein, human MeSH Prohlížeč
• ciguatoxiny MeSH
• lidokain MeSH
• mořské toxiny MeSH
• napětím řízený sodíkový kanál, typ 1 MeSH
• napětově řízený sodíkový kanál typ 11 MeSH
• napěťově řízený sodíkový kanál, typ 9 MeSH
• peptid spojený s genem pro kalcitonin MeSH
• receptory peptidu se vztahem ke genu kalcitoninu MeSH
• tetrodotoxin MeSH
• vápník MeSH

Topically applied camphor elicits a sensation of cool, but nothing is known about how it affects cold temperature sensing. We found that camphor sensitizes a subpopulation of menthol-sensitive native cutaneous nociceptors in the mouse to cold, but desensitizes and partially blocks heterologously expressed TRPM8 (transient receptor potential cation channel subfamily M member 8). In contrast, camphor reduces potassium outward currents in cultured sensory neurons and, in cold nociceptors, the cold-sensitizing effects of camphor and menthol are additive. Using a membrane potential dye-based screening assay and heterologously expressed potassium channels, we found that the effects of camphor are mediated by inhibition of Kv7.2/3 channels subtypes that generate the M-current in neurons. In line with this finding, the specific M-current blocker XE991 reproduced the cold-sensitizing effect of camphor in nociceptors. However, the M-channel blocking effects of XE991 and camphor are not sufficient to initiate cold transduction but require a cold-activated inward current generated by TRPM8. The cold-sensitizing effects of XE991 and camphor are largest in high-threshold cold nociceptors. Low-threshold corneal cold thermoreceptors that express high levels of TRPM8 and lack potassium channels are not affected by camphor. We also found that menthol--like camphor--potently inhibits Kv7.2/3 channels. The apparent functional synergism arising from TRPM8 activation and M-current block can improve the effectiveness of topical coolants and cooling lotions, and may also enhance TRPM8-mediated analgesia.

• MeSH
• kafr farmakologie   MeSH
• kationtové kanály TRPM genetika   metabolismus   MeSH
• menthol farmakologie   MeSH
• myši inbrední C57BL MeSH
• myši MeSH
• nervová vlákna nemyelinizovaná účinky léků   metabolismus   MeSH
• nízká teplota MeSH
• nociceptory metabolismus   fyziologie   MeSH
• signální transdukce účinky léků   fyziologie   MeSH
• spinální ganglia účinky léků   metabolismus   MeSH
• termoreceptory metabolismus   fyziologie   MeSH
• vnímání teploty účinky léků   fyziologie   MeSH
• zvířata MeSH
• Check Tag
• mužské pohlaví MeSH
• myši MeSH
• ženské pohlaví MeSH
• zvířata MeSH
• Publikační typ
• časopisecké články MeSH
• práce podpořená grantem MeSH
• Názvy látek
• kafr MeSH
• kationtové kanály TRPM MeSH
• menthol MeSH
• TRPM8 protein, mouse MeSH Prohlížeč