RESUMO
BACKGROUND: Migraine and other headache disorders affect a large percentage of the population and cause debilitating pain. Activation and sensitization of the trigeminal primary afferent neurons innervating the dura and cerebral vessels is a crucial step in the "headache circuit". Many dural afferent neurons respond to algesic and inflammatory agents. Given the clear role of the transient receptor potential (TRP) family of channels in both sensing chemical stimulants and mediating inflammatory pain, we investigated the expression of TRP channels in dural afferent neurons. METHODS: We used two fluorescent tracers to retrogradely label dural afferent neurons in adult mice and quantified the abundance of peptidergic and non-peptidergic neuron populations using calcitonin gene-related peptide immunoreactivity (CGRP-ir) and isolectin B4 (IB4) binding as markers, respectively. Using immunohistochemistry, we compared the expression of TRPV1 and TRPA1 channels in dural afferent neurons with the expression in total trigeminal ganglion (TG) neurons. To examine the distribution of TRPM8 channels, we labeled dural afferent neurons in mice expressing farnesylated enhanced green fluorescent protein (EGFPf) from a TRPM8 locus. We used nearest-neighbor measurement to predict the spatial association between dural afferent neurons and neurons expressing TRPA1 or TRPM8 channels in the TG. RESULTS AND CONCLUSIONS: We report that the size of dural afferent neurons is significantly larger than that of total TG neurons and facial skin afferents. Approximately 40% of dural afferent neurons exhibit IB4 binding. Surprisingly, the percentage of dural afferent neurons containing CGRP-ir is significantly lower than those of total TG neurons and facial skin afferents. Both TRPV1 and TRPA1 channels are expressed in dural afferent neurons. Furthermore, nearest-neighbor measurement indicates that TRPA1-expressing neurons are clustered around a subset of dural afferent neurons. Interestingly, TRPM8-expressing neurons are virtually absent in the dural afferent population, nor do these neurons cluster around dural afferent neurons. Taken together, our results suggest that TRPV1 and TRPA1 but not TRPM8 channels likely contribute to the excitation of dural afferent neurons and the subsequent activation of the headache circuit. These results provide an anatomical basis for understanding further the functional significance of TRP channels in headache pathophysiology.
Assuntos
Dura-Máter/metabolismo , Neurônios Aferentes/citologia , Neurônios Aferentes/metabolismo , Canais de Cátion TRPM/metabolismo , Canais de Cátion TRPV/metabolismo , Canais de Potencial de Receptor Transitório/metabolismo , Gânglio Trigeminal/citologia , Animais , Peptídeo Relacionado com Gene de Calcitonina/metabolismo , Tamanho Celular , Dura-Máter/citologia , Face/inervação , Camundongos , Camundongos Endogâmicos C57BL , Lectinas de Plantas/metabolismo , Pele/inervação , Canal de Cátion TRPA1RESUMO
BACKGROUND: The Transient Receptor Potential (TRP) ion channel TRPA1 is a key player in pain pathways. Irritant chemicals activate ion channel TRPA1 via covalent modification of N-terminal cysteines. We and others have shown that 15-Deoxy-Δ12, 14-prostaglandin J2 (15d-PGJ2) similarly activates TRPA1 and causes channel-dependent nociception. Paradoxically, 15d-PGJ2 can also be anti-nociceptive in several pain models. Here we hypothesized that activation and subsequent desensitization of TRPA1 in dorsal root ganglion (DRG) neurons underlies the anti-nociceptive property of 15d-PGJ2. To investigate this, we utilized a battery of behavioral assays and intracellular Ca2+ imaging in DRG neurons to test if pre-treatment with 15d-PGJ2 inhibited TRPA1 to subsequent stimulation. RESULTS: Intraplantar pre-injection of 15d-PGJ2, in contrast to mustard oil (AITC), attenuated acute nocifensive responses to subsequent injections of 15d-PGJ2 and AITC, but not capsaicin (CAP). Intraplantar 15d-PGJ2-administered after the induction of inflammation-reduced mechanical hypersensitivity in the Complete Freund's Adjuvant (CFA) model for up to 2 h post-injection. The 15d-PGJ2-mediated reduction in mechanical hypersensitivity is dependent on TRPA1, as this effect was absent in TRPA1 knockout mice. Ca2+ imaging studies of DRG neurons demonstrated that 15d-PGJ2 pre-exposure reduced the magnitude and number of neuronal responses to AITC, but not CAP. AITC responses were not reduced when neurons were pre-exposed to 15d-PGJ2 combined with HC-030031 (TRPA1 antagonist), demonstrating that inhibitory effects of 15d-PGJ2 depend on TRPA1 activation. Single daily doses of 15d-PGJ2, administered during the course of 4 days in the CFA model, effectively reversed mechanical hypersensitivity without apparent tolerance or toxicity. CONCLUSIONS: Taken together, our data support the hypothesis that 15d-PGJ2 induces activation followed by persistent inhibition of TRPA1 channels in DRG sensory neurons in vitro and in vivo. Moreover, we demonstrate novel evidence that 15d-PGJ2 is analgesic in mouse models of pain via a TRPA1-dependent mechanism. Collectively, our studies support that TRPA1 agonists may be useful as pain therapeutics.
Assuntos
Nociceptividade/efeitos dos fármacos , Prostaglandinas/metabolismo , Canais de Potencial de Receptor Transitório/metabolismo , Animais , Gânglios Espinais/efeitos dos fármacos , Gânglios Espinais/metabolismo , Masculino , Camundongos , Camundongos Knockout , Mostardeira , Óleos de Plantas/farmacologia , Prostaglandina D2/análogos & derivados , Prostaglandina D2/farmacologia , Canal de Cátion TRPA1 , Canais de Potencial de Receptor Transitório/genéticaRESUMO
In this issue of Neuron, Kwan et al. demonstrate that TRPA1 is critical for the transduction of noxious cold and mechanical stimuli, as well as in mediating the activation of nociceptors by endogenous and natural irritants. Differences between the present report and a previous study indicate that further study is needed to reach a consensus on the role of TRPA1 in the transduction of mechanical and noxious cold stimuli.
Assuntos
Mecanotransdução Celular/fisiologia , Dor/fisiopatologia , Transdução de Sinais/fisiologia , Canais de Potencial de Receptor Transitório/fisiologia , Animais , Temperatura Baixa , Humanos , Estimulação Física , Canal de Cátion TRPA1RESUMO
Pain perception begins with the activation of primary sensory nociceptors. Over the past decade, flourishing research has revealed that members of the Transient Receptor Potential (TRP) ion channel family are fundamental molecules that detect noxious stimuli and transduce a diverse range of physical and chemical energy into action potentials in somatosensory nociceptors. Here we highlight the roles of TRP vanilloid 1 (TRPV1), TRP melastatin 8 (TRPM8) and TRP ankyrin 1 (TRPA1) in the activation of nociceptors by heat and cold environmental stimuli, mechanical force, and by chemicals including exogenous plant and environmental compounds as well as endogenous inflammatory molecules. The contribution of these channels to pain and somatosensation is discussed at levels ranging from whole animal behavior to molecular modulation by intracellular signaling proteins. An emerging theme is that TRP channels are not simple ion channel transducers of one or two stimuli, but instead serve multidimensional roles in signaling sensory stimuli that are exceptionally diverse in modality and in their environmental milieu.
Assuntos
Sistema Nervoso/fisiopatologia , Nociceptores/fisiologia , Dor/fisiopatologia , Células Receptoras Sensoriais/fisiologia , Transdução de Sinais/fisiologia , Canais de Potencial de Receptor Transitório/fisiologia , Animais , Anquirinas/fisiologia , Humanos , Sistema Nervoso/metabolismo , Dor/metabolismo , Sensação/fisiologia , Canais de Cátion TRPM/fisiologia , Canais de Cátion TRPV/fisiologiaRESUMO
Six members of the mammalian transient receptor potential (TRP) ion channels respond to varied temperature thresholds. The natural compounds capsaicin and menthol activate noxious heat-sensitive TRPV1 and cold-sensitive TRPM8, respectively. The burning and cooling perception of capsaicin and menthol demonstrate that these ion channels mediate thermosensation. We show that, in addition to noxious cold, pungent natural compounds present in cinnamon oil, wintergreen oil, clove oil, mustard oil, and ginger all activate TRPA1 (ANKTM1). Bradykinin, an inflammatory peptide acting through its G protein-coupled receptor, also activates TRPA1. We further show that phospholipase C is an important signaling component for TRPA1 activation. Cinnamaldehyde, the most specific TRPA1 activator, excites a subset of sensory neurons highly enriched in cold-sensitive neurons and elicits nociceptive behavior in mice. Collectively, these data demonstrate that TRPA1 activation elicits a painful sensation and provide a potential molecular model for why noxious cold can paradoxically be perceived as burning pain.
Assuntos
Acroleína/análogos & derivados , Acroleína/farmacologia , Bradicinina/farmacologia , Temperatura Baixa/efeitos adversos , Canais Iônicos/efeitos dos fármacos , Canais Iônicos/metabolismo , Neurônios Aferentes/efeitos dos fármacos , Animais , Comportamento Animal/efeitos dos fármacos , Comportamento Animal/fisiologia , Células CHO , Membrana Celular/efeitos dos fármacos , Membrana Celular/metabolismo , Cricetinae , Relação Dose-Resposta a Droga , Humanos , Mediadores da Inflamação/farmacologia , Potenciais da Membrana/efeitos dos fármacos , Potenciais da Membrana/fisiologia , Camundongos , Neurônios Aferentes/metabolismo , Nociceptores/efeitos dos fármacos , Nociceptores/metabolismo , Dor/induzido quimicamente , Dor/metabolismo , Dor/fisiopatologia , Medição da Dor/efeitos dos fármacos , Ratos , Canal de Cátion TRPA1 , Canais de Potencial de Receptor Transitório , Fosfolipases Tipo C/metabolismoRESUMO
BACKGROUND: A number of prostaglandins (PGs) sensitize dorsal root ganglion (DRG) neurons and contribute to inflammatory hyperalgesia by signaling through specific G protein-coupled receptors (GPCRs). One mechanism whereby PGs sensitize these neurons is through modulation of "thermoTRPs," a subset of ion channels activated by temperature belonging to the Transient Receptor Potential ion channel superfamily. Acrid, electrophilic chemicals including cinnamaldehyde (CA) and allyl isothiocyanate (AITC), derivatives of cinnamon and mustard oil respectively, activate thermoTRP member TRPA1 via direct modification of channel cysteine residues. RESULTS: Our search for endogenous chemical activators utilizing a bioactive lipid library screen identified a cyclopentane PGD2 metabolite, 15-deoxy-Delta12,14-prostaglandin J2 (15d-PGJ2), as a TRPA1 agonist. Similar to CA and AITC, this electrophilic molecule is known to modify cysteines of cellular target proteins. Electophysiological recordings verified that 15d-PGJ2 specifically activates TRPA1 and not TRPV1 or TRPM8 (thermoTRPs also enriched in DRG). Accordingly, we identified a population of mouse DRG neurons responsive to 15d-PGJ2 and AITC that is absent in cultures derived from TRPA1 knockout mice. The irritant molecules that activate TRPA1 evoke nociceptive responses. However, 15d-PGJ2 has not been correlated with painful sensations; rather, it is considered to mediate anti-inflammatory processes via binding to the nuclear peroxisome proliferator-activated receptor gamma (PPARgamma). Our in vivo studies revealed that 15d-PGJ2 induced acute nociceptive responses when administered cutaneously. Moreover, mice deficient in the TRPA1 channel failed to exhibit such behaviors. CONCLUSION: In conclusion, we show that 15d-PGJ2 induces acute nociception when administered cutaneously and does so via a TRPA1-specific mechanism.
Assuntos
Canais de Cálcio/metabolismo , Proteínas do Tecido Nervoso/metabolismo , Nociceptores/metabolismo , Medição da Dor , Prostaglandina D2/análogos & derivados , Fenômenos Fisiológicos da Pele , Canais de Potencial de Receptor Transitório/metabolismo , Animais , Células CHO , Canais de Cálcio/fisiologia , Células Cultivadas , Cricetinae , Cricetulus , Gânglios Espinais/fisiologia , Células HeLa , Humanos , Masculino , Camundongos , Camundongos Endogâmicos C57BL , Camundongos Knockout , Proteínas do Tecido Nervoso/fisiologia , Nociceptores/fisiologia , Prostaglandina D2/fisiologia , Ratos , Transdução de Sinais/genética , Transdução de Sinais/fisiologia , Fenômenos Fisiológicos da Pele/genética , Canal de Cátion TRPA1 , Canais de Potencial de Receptor Transitório/deficiência , Canais de Potencial de Receptor Transitório/fisiologiaRESUMO
Pain is universal and vital to survival. It is an essential component of our sense of touch; together, touch and pain have evolved to enable our awareness of the intricacies of our environment and to warn us of danger and possible injury. There is a clear link between temperature sensation and pain-painful temperature sensations occur acutely and are a hallmark of inflammatory and chronic pain disorders of the nervous system. Mounting evidence suggests a subset of Transient Receptor Potential (TRP) ion channels activated by temperature (thermoTRPs) are important molecular players in acute, inflammatory and chronic pain states. Varying degrees of heat activate four of these channels (TRPV1-4), while cooling temperatures ranging from pleasant to painful activate two distantly related thermoTRP channels (TRPM8 and TRPA1). ThermoTRP channels are also chemosensitive, being activated and or modulated by plant-derived small molecules and endogenous inflammatory mediators. All thermoTRPs are expressed in tissues essential to cutaneous thermal and pain sensation. This review examines the contribution of thermoTRP channels to our understanding of temperature and pain transduction at the molecular level.
RESUMO
The ability to sense and respond to thermal stimuli at varied environmental temperatures is essential for survival in seasonal areas. In this study, we show that mice respond similarly to ramping changes in temperature from a wide range of baseline temperatures. Further investigation suggests that this ability to adapt to different ambient environments is based on rapid adjustments made to a dynamic temperature set point. The adjustment of this set point requires transient receptor potential cation channel, subfamily member 8 (TRPM8), but not transient receptor potential cation channel, subfamily A, member 1 (TRPA1), and is regulated by phospholipase C (PLC) activity. Overall, our findings suggest that temperature response thresholds in mice are dynamic, and that this ability to adapt to environmental temperature seems to mirror the in vitro findings that PLC-mediated hydrolysis of phosphoinositol 4,5-bisphosphate modulates TRPM8 activity and thereby regulates the response thresholds to cold stimuli.
Assuntos
Adaptação Fisiológica/fisiologia , Canais de Cátion TRPM/metabolismo , Sensação Térmica/fisiologia , Fosfolipases Tipo C/metabolismo , Animais , Camundongos , Canais de Cátion TRPM/genética , TemperaturaRESUMO
UNLABELLED: We used multiple pain models to investigate the effects of (-)-linalool, a monoterpene alcohol present in the essential oil of plants, on chronic inflammatory and neuropathic hypersensitivity in adult Swiss mice. Inflammatory or neuropathic hypersensitivity was induced by intraplantar (i.pl.) injection of complete Freund's adjuvant (CFA) or partial sciatic nerve ligation (PSNL), respectively. Twenty-four hours after CFA injection, we used Von Frey filaments and acetone-evoked cooling to evaluate tactile and thermal hypersensitivity, respectively. A single i.p. injection of (-)-linalool (50 or 200 mg/kg) administered 30 minutes before testing reduced CFA-induced mechanical hypersensitivity. Similarly, (-)-linalool reduced acetone-evoked hypersensitivity up to 4 hours after treatment. Compared with vehicle, (-)-linalool produced a marked reduction in CFA-induced paw edema. (-)-Linalool also reduced mechanical hypersensitivity induced by PSNL 7 days after injury. Multiple (-)-linalool treatments given chronically (twice a day for 10 days; 50 mg/kg, i.p.) significantly reduced mechanical hypersensitivity induced by CFA and PSNL. This multidose strategy did not cause tolerance. We also reasoned that (-)-linalool might reduce nociceptive behavior in response to direct administration of inflammatory mediators. Therefore, we injected the cytokines IL-1ß (.1 pg/site) and TNF-α (1 pg/site) intrathecally. (-)-Linalool inhibited the biting response induced by IL-1ß and TNF-α. PERSPECTIVE: The article adds information about antinociceptive properties of (-)-linalool in chronic inflammatory and neuropathic hypersensitivity. It also indicates that (-)-linalool might be potentially interesting in the development of new clinically relevant drugs for the management of persistent pain.
Assuntos
Mediadores da Inflamação/farmacologia , Monoterpenos/farmacologia , Neuralgia/prevenção & controle , Monoterpenos Acíclicos , Adjuvantes Imunológicos/toxicidade , Animais , Doença Crônica , Modelos Animais de Doenças , Feminino , Adjuvante de Freund/toxicidade , Hiperalgesia/tratamento farmacológico , Hiperalgesia/patologia , Hiperestesia/tratamento farmacológico , Hiperestesia/patologia , Mediadores da Inflamação/uso terapêutico , Camundongos , Monoterpenos/uso terapêutico , Neuralgia/tratamento farmacológico , Neuralgia/patologia , Neuropatia Ciática/tratamento farmacológico , Neuropatia Ciática/patologiaRESUMO
Heterologous channel expression can be used to control activity in select neuronal populations, thus expanding the tools available to modern neuroscience. However, the secondary effects of exogenous channel expression are often left unexplored. We expressed two transient receptor potential (TRP) channel family members, TRPV1 and TRPM8, in cultured hippocampal neurons. We compared functional expression levels and secondary effects of channel expression and activation on neuronal survival and signaling. We found that activation of both channels with appropriate agonist caused large depolarizing currents in voltage-clamped hippocampal neurons, exceeding the amplitude responses to a calibrating 30 mM KCl stimulation. Both TRPV1 and TRPM8 currents were reduced but not eliminated by 4 hr incubation in saturating agonist concentration. In the case of TRPV1, but not TRPM8, prolonged agonist exposure caused strong calcium-dependent toxicity. In addition, TRPV1 expression depressed synaptic transmission dramatically without overt signs of toxicity, possibly due to low-level TRPV1 activation in the absence of exogenous agonist application. Despite evidence of expression at presynaptic sites, in addition to somatodendritic sites, TRPM8 expression alone exhibited no effects on synaptic transmission. Therefore, by a number of criteria, TRPM8 proved the superior choice for control over neuronal membrane potential. This study also highlights the need to explore potential secondary effects of long-term expression and activation of heterologously introduced channels.
Assuntos
Hipocampo/citologia , Neurônios/metabolismo , Canais de Cátion TRPM/metabolismo , Canais de Cátion TRPV/metabolismo , Animais , Capsaicina/farmacologia , Ativação do Canal Iônico/efeitos dos fármacos , Mentol/farmacologia , Neurônios/efeitos dos fármacos , Neurotransmissores/metabolismo , Ratos , Rutênio Vermelho/metabolismo , Transmissão Sináptica/efeitos dos fármacos , Canais de Cátion TRPM/agonistas , Canais de Cátion TRPV/agonistas , Tetrodotoxina/farmacologia , TransfecçãoRESUMO
Several temperature-activated transient receptor potential (thermoTRP) ion channels are the molecular receptors of natural compounds that evoke thermal and pain sensations. Menthol, popularly known for its cooling effect, activates TRPM8--a cold-activated thermoTRP ion channel. However, human physiological studies demonstrate a paradoxical role of menthol in modulation of warm sensation, and here, we show that menthol also activates heat-activated TRPV3. We further show that menthol inhibits TRPA1, potentially explaining the use of menthol as an analgesic. Similar to menthol, both camphor and cinnamaldehyde (initially reported to be specific activators of TRPV3 and TRPA1, respectively) also modulate other thermoTRPs. Therefore, we find that many "sensory compounds" presumed to be specific have a promiscuous relationship with thermoTRPs.
Assuntos
Antipruriginosos/farmacologia , Mentol/farmacologia , Neurônios Aferentes/efeitos dos fármacos , Neurônios Aferentes/fisiologia , Temperatura , Animais , Animais Recém-Nascidos , Cálcio/metabolismo , Cânfora/farmacologia , Capsaicina/farmacologia , Células Cultivadas , Cricetinae , Cricetulus , Diagnóstico por Imagem/métodos , Relação Dose-Resposta a Droga , Relação Dose-Resposta à Radiação , Interações Medicamentosas , Estimulação Elétrica/métodos , Gânglios Espinais/citologia , Queratinócitos , Potenciais da Membrana/efeitos dos fármacos , Potenciais da Membrana/fisiologia , Camundongos , Técnicas de Patch-Clamp/métodos , Ratos , Transfecção/métodos , Canais de Potencial de Receptor Transitório/genética , Canais de Potencial de Receptor Transitório/fisiologiaRESUMO
Environmental temperature is thought to be directly sensed by neurons through their projections in the skin. A subset of the mammalian transient receptor potential (TRP) family of ion channels has been implicated in this process. These "thermoTRPs" are activated at distinct temperature thresholds and are typically expressed in sensory neurons. TRPV3 is activated by heat (>33 degrees C) and, unlike most thermoTRPs, is expressed in mouse keratinocytes. We found that TRPV3 null mice have strong deficits in responses to innocuous and noxious heat but not in other sensory modalities; hence, TRPV3 has a specific role in thermosensation. The natural compound camphor, which modulates sensations of warmth in humans, proved to be a specific activator of TRPV3. Camphor activated cultured primary keratinocytes but not sensory neurons, and this activity was abolished in TRPV3 null mice. Therefore, heat-activated receptors in keratinocytes are important for mammalian thermosensation.
Assuntos
Proteínas de Transporte de Cátions/fisiologia , Temperatura Alta , Canais Iônicos/fisiologia , Queratinócitos/metabolismo , Termorreceptores/fisiologia , Sensação Térmica , Animais , Bradicinina/farmacologia , Células CHO , Cânfora/farmacologia , Proteínas de Transporte de Cátions/genética , Células Cultivadas , Cricetinae , Derme/anatomia & histologia , Derme/inervação , Derme/ultraestrutura , Epiderme/anatomia & histologia , Epiderme/inervação , Epiderme/ultraestrutura , Gânglios Espinais/citologia , Gânglios Espinais/metabolismo , Humanos , Canais Iônicos/genética , Camundongos , Camundongos Endogâmicos C57BL , Camundongos Knockout , Neurônios Aferentes/fisiologia , Técnicas de Patch-Clamp , Canais de Cátion TRPV , Temperatura , Fatores de TempoRESUMO
A distinct subset of sensory neurons are thought to directly sense changes in thermal energy through their termini in the skin. Very little is known about the molecules that mediate thermoreception by these neurons. Vanilloid Receptor 1 (VR1), a member of the TRP family of channels, is activated by noxious heat. Here we describe the cloning and characterization of TRPM8, a distant relative of VR1. TRPM8 is specifically expressed in a subset of pain- and temperature-sensing neurons. Cells overexpressing the TRPM8 channel can be activated by cold temperatures and by a cooling agent, menthol. Our identification of a cold-sensing TRP channel in a distinct subpopulation of sensory neurons implicates an expanded role for this family of ion channels in somatic sensory detection.
Assuntos
Canais de Cálcio/metabolismo , Temperatura Baixa , Mentol/farmacologia , Neurônios Aferentes/efeitos dos fármacos , Neurônios Aferentes/metabolismo , Termorreceptores/metabolismo , Sequência de Aminoácidos , Animais , Antipruriginosos/farmacologia , Células CHO , Cálcio/metabolismo , Canais de Cálcio/classificação , Canais de Cálcio/genética , Clonagem Molecular , Cricetinae , Humanos , Hibridização In Situ , Camundongos , Dados de Sequência Molecular , Técnicas de Patch-Clamp , Filogenia , Alinhamento de Sequência , Canais de Cátion TRPC , Distribuição TecidualRESUMO
Mechanical and thermal cues stimulate a specialized group of sensory neurons that terminate in the skin. Three members of the transient receptor potential (TRP) family of channels are expressed in subsets of these neurons and are activated at distinct physiological temperatures. Here, we describe the cloning and characterization of a novel thermosensitive TRP channel. TRPV3 has a unique threshold: It is activated at innocuous (warm) temperatures and shows an increased response at noxious temperatures. TRPV3 is specifically expressed in keratinocytes; hence, skin cells are capable of detecting heat via molecules similar to those in heat-sensing neurons.
Assuntos
Capsaicina/análogos & derivados , Proteínas de Transporte de Cátions , Temperatura Alta , Canais Iônicos/metabolismo , Queratinócitos/metabolismo , Sequência de Aminoácidos , Animais , Animais Recém-Nascidos , Northern Blotting , Células CHO , Capsaicina/farmacologia , Linhagem Celular , Células Cultivadas , Clonagem Molecular , Cricetinae , Células Epidérmicas , Epiderme/inervação , Epiderme/metabolismo , Gânglios Espinais/metabolismo , Humanos , Hibridização In Situ , Canais Iônicos/química , Canais Iônicos/genética , Potenciais da Membrana , Camundongos , Dados de Sequência Molecular , Terminações Nervosas/fisiologia , Neurônios/fisiologia , Técnicas de Patch-Clamp , RNA Mensageiro/genética , RNA Mensageiro/metabolismo , Rutênio Vermelho/farmacologia , Transdução de Sinais , Medula Espinal/metabolismo , Canais de Cátion TRPV , TemperaturaRESUMO
Mammals detect temperature with specialized neurons in the peripheral nervous system. Four TRPV-class channels have been implicated in sensing heat, and one TRPM-class channel in sensing cold. The combined range of temperatures that activate these channels covers a majority of the relevant physiological spectrum sensed by most mammals, with a significant gap in the noxious cold range. Here, we describe the characterization of ANKTM1, a cold-activated channel with a lower activation temperature compared to the cold and menthol receptor, TRPM8. ANKTM1 is a distant family member of TRP channels with very little amino acid similarity to TRPM8. It is found in a subset of nociceptive sensory neurons where it is coexpressed with TRPV1/VR1 (the capsaicin/heat receptor) but not TRPM8. Consistent with the expression of ANKTM1, we identify noxious cold-sensitive sensory neurons that also respond to capsaicin but not to menthol.