Pungent agents from Szechuan peppers excite sensory neurons by inhibiting two-pore potassium channels

Intestinal, portal, and peripheral profiles of daikenchuto (TU-100)'s active ingredients after oral administration

A pharmaceutical grade Japanese traditional medicine, daikenchuto (TU-100), consisting of Japanese pepper, processed ginger, and ginseng, has been widely used for various intestinal disorders in Japan and now under development as a new therapeutic drug in the US. It is suggested that TU-100 ingredients exert pharmacological effects on intestines via two routes, from the luminal side before absorption and the peripheral blood stream after absorption. Therefore, in order to fully understand the pharmacological actions of TU-100, it is critically important to know the intraluminal amounts and forms of ingested TU-100 ingredients. In the present study, after administrating TU-100 to rats, the concentrations of TU-100 ingredients and their conjugates in the peripheral and portal blood and ileal contents were determined by LC-MS/MS. Next, TU-100 was administered to patients with ileostomy bags, but whose small intestines are diagnosed as healthy, and the ingredients/conjugates in the ileal effluent were analyzed. The results suggest that: (1) Pepper ingredients hydroxysanshools are rapidly absorbed and enter systemic circulation, (2) Ginseng ingredients ginsenosides are transported to the colon with the least absorption, (3) Ginger ingredients gingerols are absorbed and some conjugated in the small intestine and transported via the portal vein. While only a small amount of gingerols/gingerol conjugates enter systemic circulation, considerable amounts reappear in the small intestine. Thus, the effect of TU-100 on the intestines is believed to be a composite of multiple actions by multiple compounds supplied via multiple routes.

Complementary and synergistic therapeutic effects of compounds found in Kampo medicine: analysis of daikenchuto

Herbal medicines have been used in Japan for more than 1500 years and traditional Japanese medicines (Kampo medicines) are now fully integrated into the modern healthcare system. In total, 148 Kampo formulae are officially approved as prescription drugs and covered by the national health insurance system in Japan. However, despite their long track record of clinical use, the multi-targeted, multi-component properties of Kampo medicines, which are fundamentally different from Western medicines, have made it difficult to create a suitable framework for conducting well-designed, large-scale clinical trials. In turn, this has led to misconceptions among western trained physicians concerning the paucity of scientific evidence for the beneficial effects of Kampo medicines. Fortunately, there has been a recent surge in scientifically robust data from basic and clinical studies for some of the Kampo medicines, e.g., daikenchuto (TU-100). Numerous basic and clinical studies on TU-100, including placebo-controlled double-blind studies for various gastrointestinal disorders, and absorption, distribution, metabolism and excretion (ADME) studies, have been conducted or are in the process of being conducted in both Japan and the USA. Clinical studies suggest that TU-100 is beneficial for postoperative complications, especially ileus and abdominal bloating. ADME and basic studies indicate that the effect of TU-100 is a composite of numerous actions mediated by multiple compounds supplied via multiple routes. In addition to known mechanisms of action via enteric/sensory nerve stimulation, novel mechanisms via the TRPA1 channel and two pore domain potassium channels have recently been elucidated. TU-100 compounds target these channels with and without absorption, both before and after metabolic activation by enteric flora, with different timings and possibly with synergism.

RNA-Seq Analysis of Human Trigeminal and Dorsal Root Ganglia with a Focus on Chemoreceptors

The chemosensory capacity of the somatosensory system relies on the appropriate expression of chemoreceptors, which detect chemical stimuli and transduce sensory information into cellular signals. Knowledge of the complete repertoire of the chemoreceptors expressed in human sensory ganglia is lacking. This study employed the next-generation sequencing technique (RNA-Seq) to conduct the first expression analysis of human trigeminal ganglia (TG) and dorsal root ganglia (DRG). We analyzed the data with a focus on G-protein coupled receptors (GPCRs) and ion channels, which are (potentially) involved in chemosensation by somatosensory neurons in the human TG and DRG. For years, transient receptor potential (TRP) channels have been considered the main group of receptors for chemosensation in the trigeminal system. Interestingly, we could show that sensory ganglia also express a panel of different olfactory receptors (ORs) with putative chemosensory function. To characterize OR expression in more detail, we performed microarray, semi-quantitative RT-PCR experiments, and immunohistochemical staining. Additionally, we analyzed the expression data to identify further known or putative classes of chemoreceptors in the human TG and DRG. Our results give an overview of the major classes of chemoreceptors expressed in the human TG and DRG and provide the basis for a broader understanding of the reception of chemical cues.

Hydroxy-α sanshool induces colonic motor activity in rat proximal colon: a possible involvement of KCNK9

Various colonic motor activities are thought to mediate propulsion and mixing/absorption of colonic content. The Japanese traditional medicine daikenchuto (TU-100), which is widely used for postoperative ileus in Japan, accelerates colonic emptying in healthy humans. Hydroxy-α sanshool (HAS), a readily absorbable active ingredient of TU-100 and a KCNK3/KCNK9/KCNK18 blocker as well as TRPV1/TRPA1 agonist, has been investigated for its effects on colonic motility. Motility was evaluated by intraluminal pressure and video imaging of rat proximal colons in an organ bath. Distribution of KCNKs was investigated by RT-PCR, in situ hybridization, and immunohistochemistry. Current and membrane potential were evaluated with use of recombinant KCNK3- or KCNK9-expressing Xenopus oocytes and Chinese hamster ovary cells. Defecation frequency in rats was measured. HAS dose dependently induced strong propulsive "squeezing" motility, presumably as long-distance contraction (LDC). TRPV1/TRPA1 agonists induced different motility patterns. The effect of HAS was unaltered by TRPV1/TRPA1 antagonists and desensitization. Lidocaine (a nonselective KCNK blocker) and hydroxy-β sanshool (a geometrical isomer of HAS and KCNK3 blocker) also induced colonic motility as a rhythmic propagating ripple (RPR) and a LDC-like motion, respectively. HAS-induced "LDC," but not lidocaine-induced "RPR," was abrogated by a neuroleptic agent tetrodotoxin. KCNK3 and KCNK9 were located mainly in longitudinal smooth muscle cells and in neural cells in the myenteric plexus, respectively. Administration of HAS or TU-100 increased defecation frequency in normal and laparotomy rats. HAS may evoke strong LDC possibly via blockage of the neural KCNK9 channel in the colonic myenteric plexus.

The family of K2P channels: salient structural and functional properties

Potassium channels participate in many biological functions, from ion homeostasis to generation and modulation of the electrical membrane potential. They are involved in a large variety of diseases. In the human genome, 15 genes code for K(+) channels with two pore domains (K2P ). These channels form dimers of pore-forming subunits that produce background conductances finely regulated by a range of natural and chemical effectors, including signalling lipids, temperature, pressure, pH, antidepressants and volatile anaesthetics. Since the cloning of TWIK1, the prototypical member of this family, a lot of work has been carried out on their structure and biology. These studies are still in progress, but data gathered so far show that K2P channels are central players in many processes, including ion homeostasis, hormone secretion, cell development and excitability. A growing number of studies underline their implication in physiopathological mechanisms, such as vascular and pulmonary hypertension, cardiac arrhythmias, nociception, neuroprotection and depression. This review gives a synthetic view of the most noticeable features of these channels.

Molecular mechanisms of temperature adaptation

Thermal perception is a fundamental physiological process pertaining to the vast majority of organisms. In vertebrates, environmental temperature is detected by the primary afferents of the somatosensory neurons in the skin, which express a 'choir' of ion channels tuned to detect particular temperatures. Nearly two decades of research have revealed a number of receptor ion channels that mediate the perception of several temperature ranges, but most still remain molecularly orphaned. Yet even within this well-researched realm, most of our knowledge largely pertains to two closely related species of rodents, mice and rats. While these are standard biomedical research models, mice and rats provide a limited perspective to elucidate the general principles that drive somatosensory evolution. In recent years, significant advances have been made in understanding the molecular mechanism of temperature adaptation in evolutionarily distant vertebrates and in organisms with acute thermal sensitivity. These studies have revealed the remarkable versatility of the somatosensory system and highlighted adaptations at the molecular level, which often include changes in biophysical properties of ion channels from the transient receptor potential family. Exploiting non-standard animal models has the potential to provide unexpected insights into general principles of thermosensation and thermoregulation, unachievable using the rodent model alone.

Diacylglycerol mediates regulation of TASK potassium channels by Gq-coupled receptors

The two-pore domain potassium (K2P) channels TASK-1 (KCNK3) and TASK-3 (KCNK9) are important determinants of background K(+) conductance and membrane potential. TASK-1/3 activity is regulated by hormones and transmitters that act through G protein-coupled receptors (GPCR) signalling via G proteins of the Gαq/11 subclass. How the receptors inhibit channel activity has remained unclear. Here, we show that TASK-1 and -3 channels are gated by diacylglycerol (DAG). Receptor-initiated inhibition of TASK required the activity of phospholipase C, but neither depletion of the PLC substrate PI(4,5)P2 nor release of the downstream messengers IP3 and Ca(2+). Attenuation of cellular DAG transients by DAG kinase or lipase suppressed receptor-dependent inhibition, showing that the increase in cellular DAG-but not in downstream lipid metabolites-mediates channel inhibition. The findings identify DAG as the signal regulating TASK channels downstream of GPCRs and define a novel role for DAG that directly links cellular DAG dynamics to excitability.

Properties, regulation, pharmacology, and functions of the K₂p channel, TRESK

TWIK-related spinal cord K(+) channel (TRESK) is the gene product of KCNK18, the last discovered leak potassium K2P channel gene. Under resting conditions, TRESK is constitutively phosphorylated at two regulatory regions. Protein kinase A (PKA) and microtubule affinity-regulating (MARK) kinases can be applied in experiments to phosphorylate these sites of TRESK expressed in Xenopus oocytes, respectively. Upon generation of a calcium signal, TRESK is dephosphorylated and thereby activated by calcineurin. In this process, the binding of calcineurin to the channel by non-catalytic interacting sites is essential. The phosphorylation/dephosphorylation regulatory process is modified by 14-3-3 proteins. Human, but not murine TRESK is also activated by protein kinase C. TRESK is expressed most abundantly in sensory neurons of the dorsal root ganglia (DRG) and trigeminal ganglia, and the channel modifies certain forms of nociceptive afferentation. In a large pedigree, a dominant negative mutant TRESK allele was found to co-segregate perfectly with migraine phenotype. While this genetic defect may be responsible only for a very small fraction of migraine cases, specific TRESK activation is expected to exert beneficial effect in common forms of the disease.

The LQLP calcineurin docking site is a major determinant of the calcium-dependent activation of human TRESK background K+ channel

Calcium-dependent activation of human TRESK (TWIK-related spinal cord K(+) channel, K2P18.1) depends on direct targeting of calcineurin to the PQIIIS motif. In the present study we demonstrate that TRESK also contains another functionally relevant docking site for the phosphatase, the LQLP amino acid sequence. Combined mutations of the PQIIIS and LQLP motifs were required to eliminate the calcium-dependent regulation of the channel. In contrast to the alanine substitutions of PQIIIS, the mutation of LQLP to AQAP alone did not significantly change the amplitude of TRESK activation evoked by the substantial elevation of cytoplasmic calcium concentration. However, the AQAP mutation slowed down the response to high calcium. In addition, modest elevation of [Ca(2+)], which effectively regulated the wild type channel, failed to activate TRESK-AQAP. This indicates that the AQAP mutation diminished the sensitivity of TRESK to calcium. Even if PQIIIS was replaced by the PVIVIT sequence of high calcineurin binding affinity, the effect of the AQAP mutation was clearly detected in this TRESK-PVIVIT context. Substitution of the LQLP region with the corresponding fragment of NFAT transcription factor, perfectly matching the previously described LXVP calcineurin-binding consensus sequence, increased the calcium-sensitivity of TRESK-PVIVIT. Thus the enhancement of the affinity of TRESK for calcineurin by the incorporation of PVIVIT could not compensate for or prevent the effects of LQLP sequence modifications, suggesting that the two calcineurin-binding regions play distinct roles in the regulation. Our results indicate that the LQLP site is a fundamental determinant of the calcium-sensitivity of human TRESK.

Control of somatic membrane potential in nociceptive neurons and its implications for peripheral nociceptive transmission

Peripheral sensory ganglia contain somata of afferent fibres conveying somatosensory inputs to the central nervous system. Growing evidence suggests that the somatic/perisomatic region of sensory neurons can influence peripheral sensory transmission. Control of resting membrane potential (E_rest) is an important mechanism regulating excitability, but surprisingly little is known about how E_rest is regulated in sensory neuron somata or how changes in somatic/perisomatic E_rest affect peripheral sensory transmission. We first evaluated the influence of several major ion channels on E_rest in cultured small-diameter, mostly capsaicin-sensitive (presumed nociceptive) dorsal root ganglion (DRG) neurons. The strongest and most prevalent effect on E_rest was achieved by modulating M channels, K2P and 4-aminopiridine-sensitive K_V channels, while hyperpolarization-activated cyclic nucleotide-gated, voltage-gated Na⁺, and T-type Ca²⁺ channels to a lesser extent also contributed to E_rest. Second, we investigated how varying somatic/perisomatic membrane potential, by manipulating ion channels of sensory neurons within the DRG, affected peripheral nociceptive transmission in vivo. Acute focal application of M or K_ATP channel enhancers or a hyperpolarization-activated cyclic nucleotide-gated channel blocker to L5 DRG in vivo significantly alleviated pain induced by hind paw injection of bradykinin. Finally, we show with computational modelling how somatic/perisomatic hyperpolarization, in concert with the low-pass filtering properties of the t-junction within the DRG, can interfere with action potential propagation. Our study deciphers a complement of ion channels that sets the somatic E_rest of nociceptive neurons and provides strong evidence for a robust filtering role of the somatic and perisomatic compartments of peripheral nociceptive neuron.

Nonmigraine-associated TRESK K+ channel variant C110R does not increase the excitability of trigeminal ganglion neurons

Recent genetic studies suggest that dysfunction of ion channels and transporters may contribute to migraine pathophysiology. A migraine-associated frameshift mutation in the TWIK-related spinal cord K+ (TRESK) channel results in nonfunctional channels. Moreover, mutant TRESK subunits exert a dominant-negative effect on whole cell TRESK currents and result in hyperexcitability of small-diameter trigeminal ganglion (TG) neurons, suggesting that mutant TRESK may increase the gain of the neuronal circuit underlying migraine headache. However, the nonmigraine-associated TRESK C110R variant exhibits the same effect on TRESK currents as the mutant subunits in Xenopus oocytes, suggesting that dysfunction of TRESK is not sufficient to cause migraine. Here, we confirmed that the C110R variant formed nonfunctional channels and exerted a dominant-negative effect on TRESK currents in HEK293T cells, similar to the migraine-associated mutant TRESK. To compare the functional consequences of TRESK mutations/variants in a more physiological setting, we expressed the mutant TRESK and the C110R variant in cultured mouse TG neurons and investigated their effects on background K+ currents and neuronal excitability. Both mutant TRESK and the C110R variant reduced the endogenous TRESK currents in TG neurons, but the effect of the C110R variant was significantly smaller. Importantly, only TG neurons expressing mutant TRESK subunits, but not those expressing the C110R variant, exhibited a significant increase in excitability. Thus only the migraine-associated TRESK mutation, but not the C110R variant, reduces the endogenous TRESK currents to a degree that affects TG excitability. Our results support a potential causal relationship between the frameshift TRESK mutation and migraine susceptibility.

All-trans-configuration in Zanthoxylum alkylamides swaps the tingling with a numbing sensation and diminishes salivation

The methanol soluble prepared from a supercritical fluid extract of Szechuan pepper (Zanthoxylum piperitum) was screened for its key tingling and numbing chemosensates by application of taste dilution analysis. Further separation of fractions perceived with the highest sensory impact, followed by LC-TOF-MS, LC-MS, and 1D/2D NMR experiments, led to the structure determination of the known alkylamides hydroxy-γ-sanshool (1), hydroxy-α-sanshool (2), hydroxy-β-sanshool (3), bungeanool (4), isobungeanool (5), and hydroxy-γ-isosanshool (6), as well as hydroxy-ε-sanshool (7), the structure of which has not yet been confirmed by NMR, and hydroxy-ζ-sanshool (8), which has not been previously reported in the literature. Psychophysical half-tongue experiments using filter paper rectangles (1 × 2 cm) as the vehicle revealed amides 1, 2, 4, 5, 7, and 8, showing at least one cis-configured double bond, elicited the well-known tingling and paresthetic orosensation above threshold levels of 3.5-8.3 nmol/cm(2). In contrast, the all-trans-configured amides 3 and 6 induced a numbing and anesthetic sensation above thresholds of 3.9 and 7.1 nmol/cm(2), respectively. Interestingly, the mono-cis-configured major amide 2 was found to induce massive salivation, whereas the all-trans-configuration of 3 did not.

Over-expression of TRESK K(+) channels reduces the excitability of trigeminal ganglion nociceptors

TWIK-related spinal cord K⁺ (TRESK) channel is abundantly expressed in trigeminal ganglion (TG) and dorsal root ganglion neurons and is one of the major background K⁺ channels in primary afferent neurons. Mutations in TRESK channels are associated with familial and sporadic migraine. In rats, both chronic nerve injury and inflammation alter the expression level of TRESK mRNA. Functional studies indicate that reduction of endogenous TRESK channel activity results in hyper-excitation of primary afferent neurons, suggesting that TRESK is a potential target for the development of new analgesics. However, whether and how enhancing TRESK channel activity would decrease the excitability of primary afferent neurons has not been directly tested. Here, we over-expressed TRESK subunits in cultured mouse TG neurons by lipofectamine-mediated transfection and investigated how this altered the membrane properties and the excitability of the small-diameter TG population. To account for the heterogeneity of neurons, we further divided small TG neurons into two groups, based on their ability to bind to fluorescently-labeled isolectin B (IB4). The transfected TG neurons showed a 2-fold increase in the level of TRESK proteins. This was accompanied by a significant increase in the fraction of lamotrigine-sensitive persistent K⁺ currents as well as the size of total background K⁺ currents. Consequently, both IB4-positive and IB4-negative TG neurons over-expressing TRESK subunits exhibited a lower input resistance and a 2-fold increase in the current threshold for action potential initiation. IB4-negative TG neurons over-expressing TRESK subunits also showed a significant reduction of the spike frequency in response to supra-threshold stimuli. Importantly, an increase in TRESK channel activity effectively inhibited capsaicin-evoked spikes in TG neurons. Taken together, our results suggest that potent and specific TRESK channel openers likely would reduce the excitability of primary afferent neurons and therefore are potential therapeutics for the treatment of migraine and other chronic pain symptoms.

K(+) channels: function-structural overview

Potassium channels are particularly important in determining the shape and duration of the action potential, controlling the membrane potential, modulating hormone secretion, epithelial function and, in the case of those K(+) channels activated by Ca(2+), damping excitatory signals. The multiplicity of roles played by K(+) channels is only possible to their mammoth diversity that includes at present 70 K(+) channels encoding genes in mammals. Today, thanks to the use of cloning, mutagenesis, and the more recent structural studies using x-ray crystallography, we are in a unique position to understand the origins of the enormous diversity of this superfamily of ion channels, the roles they play in different cell types, and the relations that exist between structure and function. With the exception of two-pore K(+) channels that are dimers, voltage-dependent K(+) channels are tetrameric assemblies and share an extremely well conserved pore region, in which the ion-selectivity filter resides. In the present overview, we discuss in the function, localization, and the relations between function and structure of the five different subfamilies of K(+) channels: (a) inward rectifiers, Kir; (b) four transmembrane segments-2 pores, K2P; (c) voltage-gated, Kv; (d) the Slo family; and (e) Ca(2+)-activated SK family, SKCa.

Potassium channels in peripheral pain pathways: expression, function and therapeutic potential

Electrical excitation of peripheral somatosensory nerves is a first step in generation of most pain signals in mammalian nervous system. Such excitation is controlled by an intricate set of ion channels that are coordinated to produce a degree of excitation that is proportional to the strength of the external stimulation. However, in many disease states this coordination is disrupted resulting in deregulated peripheral excitability which, in turn, may underpin pathological pain states (i.e. migraine, neuralgia, neuropathic and inflammatory pains). One of the major groups of ion channels that are essential for controlling neuronal excitability is potassium channel family and, hereby, the focus of this review is on the K+ channels in peripheral pain pathways. The aim of the review is threefold. First, we will discuss current evidence for the expression and functional role of various K+ channels in peripheral nociceptive fibres. Second, we will consider a hypothesis suggesting that reduced functional activity of K+ channels within peripheral nociceptive pathways is a general feature of many types of pain. Third, we will evaluate the perspectives of pharmacological enhancement of K+ channels in nociceptive pathways as a strategy for new analgesic drug design.

Antinociceptive effects of ethanolic extract from the flowers of Acmella oleracea (L.) R.K. Jansen in mice

ETHNOPHARMACOLOGICAL RELEVANCE

In Brazil, Acmella oleracea (L.) R.K. Jansen, popularly known as "jambu", has been used by some communities from Amazon region to treat toothache. In this study we examined the antinociceptive effect of the ethanolic extract obtained from the flowers of Acmella oleracea (EEAO) in animal models of nociceptive (chemical and thermal) and neuropathic (partial sciatic nerve ligation) pain.

MATERIALS AND METHODS

Adult male mice were treated by intraperitoneal route (i.p.) with EEAO before the induction of nociceptive response by formalin, capsaicin and cinnamaldehyde, thermal heat hyperalgesia (hot plate test) and mechanical allodynia (traumatic sciatic nerve injury). Acute toxicity and non-specific sedative effects were evaluated.

RESULTS

EEAO (10, 30 and 100 mg/kg) reduced both neurogenic and inflammatory phases of the formalin- and also capsaicin- and cinnamaldehyde-induced orofacial nociception. Interestingly, EEAO at 100mg/kg (i.p.) also reversed capsaicin-induced heat hyperalgesia assessed as the latency to paw withdrawal in the hot plate test. Also in the hot plate test, paw withdrawal latency was increased by EEAO (100 mg/kg) and this response was only partially reversed by naloxone. Furthermore, EEAO (100 mg/kg) also reduced mechanical allodynia caused by partial sciatic nerve ligation for 3 h. The estimated LD50 value was 889.14 mg/kg and EEAO did not alter the locomotion of animals in the open-field test.

CONCLUSION

Taken together, our data show that EEAO produces prevalent antinociceptive effects and does not cause adverse effects. The presence of N-alkylamides, including spilanthol, suggests that the therapeutic effect of EEAO is related to its highest anesthetic activity.

The pungent substances piperine, capsaicin, 6-gingerol and polygodial inhibit the human two-pore domain potassium channels TASK-1, TASK-3 and TRESK

For a long time, the focus of trigeminal chemoperception has rested almost exclusively on TRP channels. However, two-pore domain (K_2P) potassium channels have recently been identified as targets for substances associated with typical trigeminal sensations, such as numbing and tingling. In addition, they have been shown to be modulated by several TRP agonists. We investigated whether the pungent substances piperine, capsaicin, 6-gingerol and polygodial have an effect on human K_2P channels. For this purpose, we evaluated the effects of these pungent substances on both wild-type and mutant K_2P channels by means of two-electrode voltage-clamp experiments using Xenopus laevis oocytes. All four pungent substances were found to inhibit the basal activity of TASK-1 (K_2P 3.1), TASK-3 (K_2P 9.1), and TRESK (K_2P 18.1) channels. This inhibitory effect was dose-dependent and, with the exception of polygodial on TASK-1, fully reversible. However, only piperine exhibited an IC₅₀ similar to its reported EC₅₀ on TRP channels. Finally, we observed for TASK-3 that mutating H98 to E markedly decreased the inhibition induced by piperine, capsaicin, and 6-gingerol, but not by polygodial. Our data contribute to the relatively sparse knowledge concerning the pharmacology of K_2P channels and also raise the question of whether K_2P channels could be involved in the pungency perception of piperine.

Comprehensive RNA-Seq expression analysis of sensory ganglia with a focus on ion channels and GPCRs in Trigeminal ganglia

The specific functions of sensory systems depend on the tissue-specific expression of genes that code for molecular sensor proteins that are necessary for stimulus detection and membrane signaling. Using the Next Generation Sequencing technique (RNA-Seq), we analyzed the complete transcriptome of the trigeminal ganglia (TG) and dorsal root ganglia (DRG) of adult mice. Focusing on genes with an expression level higher than 1 FPKM (fragments per kilobase of transcript per million mapped reads), we detected the expression of 12984 genes in the TG and 13195 in the DRG. To analyze the specific gene expression patterns of the peripheral neuronal tissues, we compared their gene expression profiles with that of the liver, brain, olfactory epithelium, and skeletal muscle. The transcriptome data of the TG and DRG were scanned for virtually all known G-protein-coupled receptors (GPCRs) as well as for ion channels. The expression profile was ranked with regard to the level and specificity for the TG. In total, we detected 106 non-olfactory GPCRs and 33 ion channels that had not been previously described as expressed in the TG. To validate the RNA-Seq data, in situ hybridization experiments were performed for several of the newly detected transcripts. To identify differences in expression profiles between the sensory ganglia, the RNA-Seq data of the TG and DRG were compared. Among the differentially expressed genes (> 1 FPKM), 65 and 117 were expressed at least 10-fold higher in the TG and DRG, respectively. Our transcriptome analysis allows a comprehensive overview of all ion channels and G protein-coupled receptors that are expressed in trigeminal ganglia and provides additional approaches for the investigation of trigeminal sensing as well as for the physiological and pathophysiological mechanisms of pain.

Novel TASK channels inhibitors derived from dihydropyrrolo[2,1-a]isoquinoline

TASK channels belong to the family of K(+) channels with 4 transmembrane segments and 2 pore domains (4TM/2P) per subunit. These channels have been related to apoptosis in cerebellar granule neurons (CGN), as well as cancer in other tissues. TASK current is regulated by hormones, neurotransmitters, anesthetics and divalent cations, which are not selective. Recently, there has been found some organic compounds that inhibit TASK current selectively. In order to find other modulators, we report here a group of five dihydropyrrolo[2,1-a]isoquinolines (DPIs), four of them with putative anticancer activity, that were evaluated on TASK-1 and TASK-3 channels. The compounds 1, 2 and 3 showed IC50 < 320 μM on TASK-1 and TASK-3, intermediate activity on TASK-1/TASK-3 heterodimer, moderate effect over hslo and TREK-1 (500 μM), and practically not inhibition on Shaker-IR, herg and IRK2.1 potassium channels, when they were expressed heterologously in Xenopus laevis oocytes. In rat CGN, 500 μM of these three compounds induced a decrement by >39% of the TASK-carried leak current. Finally, only compound 1 showed significant protection (∼36%) against apoptotic death of CGN induced by K(+) deprivation. These results suggest that DPI compounds could be potential candidates for designing new selective inhibitors of TASK channels.

Transient receptor potential channels encode volatile chemicals sensed by rat trigeminal ganglion neurons

Primary sensory afferents of the dorsal root and trigeminal ganglia constantly transmit sensory information depicting the individual’s physical and chemical environment to higher brain regions. Beyond the typical trigeminal stimuli (e.g. irritants), environmental stimuli comprise a plethora of volatile chemicals with olfactory components (odorants). In spite of a complete loss of their sense of smell, anosmic patients may retain the ability to roughly discriminate between different volatile compounds. While the detailed mechanisms remain elusive, sensory structures belonging to the trigeminal system seem to be responsible for this phenomenon. In order to gain a better understanding of the mechanisms underlying the activation of the trigeminal system by volatile chemicals, we investigated odorant-induced membrane potential changes in cultured rat trigeminal neurons induced by the odorants vanillin, heliotropyl acetone, helional, and geraniol. We observed the dose-dependent depolarization of trigeminal neurons upon application of these substances occurring in a stimulus-specific manner and could show that distinct neuronal populations respond to different odorants. Using specific antagonists, we found evidence that TRPA1, TRPM8, and/or TRPV1 contribute to the activation. In order to further test this hypothesis, we used recombinantly expressed rat and human variants of these channels to investigate whether they are indeed activated by the odorants tested. We additionally found that the odorants dose-dependently inhibit two-pore potassium channels TASK1 and TASK3 heterologously expressed In Xenopus laevis oocytes. We suggest that the capability of various odorants to activate different TRP channels and to inhibit potassium channels causes neuronal depolarization and activation of distinct subpopulations of trigeminal sensory neurons, forming the basis for a specific representation of volatile chemicals in the trigeminal ganglia.

Food vibrations: Asian spice sets lips trembling

Szechuan pepper, a widely used ingredient in the cuisine of many Asian countries, is known for the tingling sensation it induces on the tongue and lips. While the molecular mechanism by which Szechuan pepper activates tactile afferent fibres has been clarified, the tingling sensation itself has been less studied, and it remains unclear which fibres are responsible. We investigated the somatosensory perception of tingling in humans to identify the characteristic temporal frequency and compare this to the established selectivity of tactile afferents. Szechuan pepper was applied to the lower lip of participants. Participants judged the frequency of the tingling sensation on the lips by comparing this with the frequencies of mechanical vibrations applied to their right index finger. The perceived frequency of the tingling was consistently at around 50 Hz, corresponding to the range of tactile RA1 afferent fibres. Furthermore, adaptation of the RA1 channel by prolonged mechanical vibration reliably reduced the tingling frequency induced by Szechuan pepper, confirming that the frequency-specific tactile channel is shared between Szechuan pepper and mechanical vibration. Combining information about molecular reactions at peripheral receptors with quantitative psychophysical measurement may provide a unique method for characterizing unusual experiences by decomposing them into identifiable minimal units of sensation.

Functional analysis of a migraine-associated TRESK K+ channel mutation

Recent genetic and functional studies suggest that migraine may result from abnormal activities of ion channels and transporters. A frameshift mutation in the human TWIK-related spinal cord K(+) (TRESK) channel has been identified in migraine with aura patients in a large pedigree. In Xenopus oocytes, mutant TRESK subunits exert a dominant-negative effect on whole-cell TRESK currents. However, questions remain as to whether and how mutant TRESK subunits affect the membrane properties and the excitability of neurons in the migraine circuit. Here, we investigated the functional consequences of the mutant TRESK subunits in HEK293T cells and mouse trigeminal ganglion (TG) neurons. First, we found that mutant TRESK subunits exhibited dominant-negative effects not only on the size of the whole-cell TRESK currents, but also on the level of TRESK channels on the plasma membrane in HEK293T cells. This likely resulted from the heterodimerization of wild-type and mutant TRESK subunits. Next, we expressed mutant TRESK subunits in cultured TG neurons and observed a significant decrease in the lamotrigine-sensitive K(+) current, suggesting that the mutant TRESK subunits have a dominant-negative effect on currents through the endogenous TRESK channels. Current-clamp recordings showed that neurons expressing mutant TRESK subunits had a higher input resistance, a lower current threshold for action potential initiation, and a higher spike frequency in response to suprathreshold stimuli, indicating that the mutation resulted in hyperexcitability of TG neurons. Our results suggest a possible mechanism through which the TRESK mutation increases the susceptibility of migraine headache.

Eugenol and carvacrol induce temporally desensitizing patterns of oral irritation and enhance innocuous warmth and noxious heat sensation on the tongue

Eugenol and carvacrol, from the spices clove and oregano, respectively, are agonists of TRPV3, which is implicated in transduction of warmth and possibly heat pain. We investigated the temporal dynamics of lingual irritation elicited by these agents, and their effects on innocuous warmth and heat pain, using a half-tongue method in human subjects. The irritant sensation elicited by both eugenol and carvacrol decreased across repeated applications at a 1-minute interstimulus interval (self-desensitization) which persisted for at least 10 minutes. Both agents also cross-desensitized capsaicin-evoked irritation. Eugenol and carvacrol significantly increased the magnitude of perceived innocuous warmth (44 °C) for >10 minutes, and briefly (<5 minutes) enhanced heat pain elicited by a 49 °C stimulus. Similar albeit weaker effects were observed when thermal stimuli were applied after the tongue had been desensitized by repeated application of eugenol or carvacrol, indicating that the effect is not due solely to summation of chemoirritant and thermal sensations. Neither chemical affected sensations of innocuous cool or cold pain. A separate group of subjects was asked to subdivide eugenol and carvacrol irritancy into subqualities, the most frequently reported being numbing and warmth, with brief burning, stinging/pricking, and tingle, confirming an earlier study. Eugenol, but not carvacrol, reduced detection of low-threshold mechanical stimuli. Eugenol and carvacrol enhancement of innocuous warmth may involve sensitization of thermal gating of TRPV3 expressed in peripheral warm fibers. The brief heat hyperalgesia following eugenol may involve a TRPV3-mediated enhancement of thermal gating of TRPV1 expressed in lingual polymodal nociceptors.

Modulation of TRESK background K+ channel by membrane stretch

The two-pore domain K⁺ channel TRESK is expressed in dorsal root ganglion and trigeminal sensory neurons where it is a major contributor to background K⁺ current. TRESK acts as a break to prevent excessive sensory neuron activation and decreases in its expression or function have been involved in neuronal hyperexcitability after injury/inflammation, migraine or altered sensory perception (tingling, cooling and pungent burning sensations). All these effects have implicated this channel in nociception and mechanotransduction. To determine the role of TRESK in sensory transduction, we studied its sensitivity to changes in membrane tension (stretch) in heterologous systems, F-11 cells and trigeminal neurons. Laminar shear stress increased TRESK currents by 22–30%. An increase in membrane tension induced by cell swelling (hypotonic medium) produced a reversible elevation of TRESK currents (39.9%). In contrast, cell shrinkage (hypertonic solution) produced the opposite effect. Membrane crenators or cup-formers produced equivalent effects. In trigeminal sensory neurons, TRESK channels were mechanically stimulated by negative pressure, which led to a 1.51-fold increase in channel open probability. TRESK-like currents in trigeminal neurons were additively inhibited by arachidonic acid, acidic pH and hypertonic stimulation, conditions usually found after tissue inflammation. Our results show that TRESK is modulated by changes in cell membrane tension and/or cell volume. Several key players released during inflammation or tissue injury could modulate sensory neuron activation through small changes in membrane tension.

A 'toothache tree' alkylamide inhibits Aδ mechanonociceptors to alleviate mechanical pain

In traditional medicine, the 'toothache tree' and other plants of the Zanthoxylum genus have been used to treat inflammatory pain conditions, such as toothache and rheumatoid arthritis. Here we examined the cellular and molecular mechanisms underlying the analgesic properties of hydroxy-α-sanshool, the active alkylamide produced by Zanthoxylum plants. Consistent with its analgesic effects in humans, sanshool treatment in mice caused a selective attenuation of mechanical sensitivity under naïve and inflammatory conditions, with no effect on thermal sensitivity. To elucidate the molecular mechanisms by which sanshool attenuates mechanical pain, we performed single fibre recordings, calcium imaging and whole-cell electrophysiology of cultured sensory neurons. We found that: (1) sanshool potently inhibits Aδ mechanonociceptors that mediate both sharp acute pain and inflammatory pain; (2) sanshool inhibits action potential firing by blocking voltage-gated sodium currents in a subset of somatosensory neurons, which express a unique combination of voltage-gated sodium channels; and (3) heterologously expressed Nav1.7 is most strongly inhibited by sanshool as compared to other sodium channels expressed in sensory neurons. These results suggest that sanshool targets voltage-gated sodium channels on Aδ mechanosensory nociceptors to dampen excitability and thus induce 'fast pain' analgesia.

Hairy Sensation

The hairs of the skin not only function to prevent heat loss but also have important sensory functions. Recent work has now established that each hair of the skin is innervated by one or more of three types of mechanoreceptor ending. Each of these three mechanoreceptor types possesses distinct molecular features and detects distinctive information about skin touch, which is relayed to specific brain locations in a somatotopic fashion.

Touch sense: functional organization and molecular determinants of mechanosensitive receptors

Cutaneous mechanoreceptors are localized in the various layers of the skin where they detect a wide range of mechanical stimuli, including light brush, stretch, vibration and noxious pressure. This variety of stimuli is matched by a diverse array of specialized mechanoreceptors that respond to cutaneous deformation in a specific way and relay these stimuli to higher brain structures. Studies across mechanoreceptors and genetically tractable sensory nerve endings are beginning to uncover touch sensation mechanisms. Work in this field has provided researchers with a more thorough understanding of the circuit organization underlying the perception of touch. Novel ion channels have emerged as candidates for transduction molecules and properties of mechanically gated currents improved our understanding of the mechanisms of adaptation to tactile stimuli. This review highlights the progress made in characterizing functional properties of mechanoreceptors in hairy and glabrous skin and ion channels that detect mechanical inputs and shape mechanoreceptor adaptation.

A role for TREK1 in generating the slow afterhyperpolarization in developing starburst amacrine cells

Slow afterhyperpolarizations (sAHPs) play an important role in establishing the firing pattern of neurons that in turn influence network activity. sAHPs are mediated by calcium-activated potassium channels. However, the molecular identity of these channels and the mechanism linking calcium entry to their activation are still unknown. Here we present several lines of evidence suggesting that the sAHPs in developing starburst amacrine cells (SACs) are mediated by two-pore potassium channels. First, we use whole cell and perforated patch voltage clamp recordings to characterize the sAHP conductance under different pharmacological conditions. We find that this conductance was calcium dependent, reversed at EK, blocked by barium, insensitive to apamin and TEA, and activated by arachidonic acid. In addition, pharmacological inhibition of calcium-activated phosphodiesterase reduced the sAHP. Second, we performed gene profiling on isolated SACs and found that they showed strong preferential expression of the two-pore channel gene kcnk2 that encodes TREK1. Third, we demonstrated that TREK1 knockout animals exhibited an altered frequency of retinal waves, a frequency that is set by the sAHPs in SACs. With these results, we propose a model in which depolarization-induced decreases in cAMP lead to disinhibition of the two-pore potassium channels and in which the kinetics of this biochemical pathway dictate the slow activation and deactivation of the sAHP conductance. Our model offers a novel pathway for the activation of a conductance that is physiologically important.

Isobutylhydroxyamides from the pericarp of Nepalese Zanthoxylum armatum inhibit NF1-defective tumor cell line growth

A neurofibromatosis type 1 (NF1)-based bioassay-guided phytochemical investigation on Zanthoxylum armatum collected in Nepal led to the isolation of new timuramides A-D (1-4) and six known sanshools (5-10). The structures of all compounds were established by using modern spectroscopic techniques, including 1D and 2D NMR analysis and comparison with previously reported data. Most of the compounds inhibited growth of an Nf1- and p53-deficient mouse glioma cell line at noncytotoxic concentrations.

Targeting two-pore domain potassium channels - a promising strategy for treating T cell mediated autoimmunity

Two-pore domain potassium channels, such as TASK, are essential players in the regulation of the resting membrane potential. A recent publication in Experimental Neurology revealed that the pharmacological blockade of the two-pore domain potassium channel TASK1 improved clinical disease severity, the number of cellular infiltrates, as well as the degree of demyelination in experimental autoimmune encephalomyelitis, an animal model for multiple sclerosis. This effect was driven by a reduction in the generation of proinflammatory cytokines and proliferation of T lymphocytes. Thus, functional activity of T lymphocytes was identified to be TASK1 dependent suggesting that this class of potassium channels may represent an interesting target for treating T cell-driven autoimmunity directed against the central nervous system.

Spices: the savory and beneficial science of pungency

Spicy food does not only provide an important hedonic input in daily life, but has also been anedoctically associated to beneficial effects on our health. In this context, the discovery of chemesthetic trigeminal receptors and their spicy ligands has provided the mechanistic basis and the pharmacological means to investigate this enticing possibility. This review discusses in molecular terms the connection between the neurophysiology of pungent spices and the "systemic" effects associated to their trigeminality. It commences with a cultural and historical overview on the Western fascination for spices, and, after analysing in detail the mechanisms underlying the trigeminality of food, the main dietary players from the transient receptor potential (TRP) family of cation channels are introduced, also discussing the "alien" distribution of taste receptors outside the oro-pharingeal cavity. The modulation of TRPV1 and TRPA1 by spices is next described, discussing how spicy sensations can be turned into hedonic pungency, and analyzing the mechanistic bases for the health benefits that have been associated to the consumption of spices. These include, in addition to a beneficial modulation of gastro-intestinal and cardio-vascular function, slimming, the optimization of skeletal muscle performance, the reduction of chronic inflammation, and the prevention of metabolic syndrome and diabetes. We conclude by reviewing the role of electrophilic spice constituents on cancer prevention in the light of their action on pro-inflammatory and pro-cancerogenic nuclear factors like NFκB, and on their interaction with the electrophile sensor protein Keap1 and the ensuing Nrf2-mediated transcriptional activity. Spicy compounds have a complex polypharmacology, and just like any other bioactive agent, show a balance of beneficial and bad actions. However, at least for moderate consumption, the balance seems definitely in favour of the positive side, suggesting that a spicy diet, a caveman-era technology, could be seriously considered in addition to caloric control and exercise as a measurement to prevent and control many chronic diseases associate to malnutrition from a Western diet.

Total synthesis of hydroxy-α- and hydroxy-β-sanshool using Suzuki-Miyaura coupling

Here, we describe the first total synthesis of hydroxyl-α- and hydroxyl-β-sanshool, which involves Suzuki-Miyaura coupling (SMC). Hydroxy-α-sanshool (1) was synthesized by SMC of bromoalkyne 4 with boronate 3 followed by (Z)-selective reduction of the triple bond in the coupling product. Hydroxy-β-sanshool (2) was synthesized by regio- and (E)-selective conversion of 4 to iodoalkene 11 followed by SMC with 3.

SUMOylation silences heterodimeric TASK potassium channels containing K2P1 subunits in cerebellar granule neurons

The standing outward K(+) current (IKso) governs the response of cerebellar granule neurons to natural and medicinal stimuli including volatile anesthetics. We showed that SUMOylation silenced half of IKso at the surface of cerebellar granule neurons because the underlying channels were heterodimeric assemblies of K2P1, a subunit subject to SUMOylation, and the TASK (two-P domain, acid-sensitive K(+)) channel subunits K2P3 or K2P9. The heterodimeric channels comprised the acid-sensitive portion of IKso and mediated its response to halothane. We anticipate that SUMOylation also influences sensation and homeostatic mechanisms in mammals through TASK channels formed with K2P1.

PKC-dependent activation of human K(2P) 18.1 K(+) channels

BACKGROUND AND PURPOSE

Two-pore-domain K(+) channels (K(2P) ) mediate K(+) background currents that modulate the membrane potential of excitable cells. K(2P) 18.1 (TWIK-related spinal cord K(+) channel) provides hyperpolarizing background currents in neurons. Recently, a dominant-negative loss-of-function mutation in K(2P) 18.1 has been implicated in migraine, and activation of K(2P) 18.1 channels was proposed as a therapeutic strategy. Here we elucidated the molecular mechanisms underlying PKC-dependent activation of K(2P) 18.1 currents.

EXPERIMENTAL APPROACH

Human K(2P) 18.1 channels were heterologously expressed in Xenopus laevis oocytes, and currents were recorded with the two-electrode voltage clamp technique.

KEY RESULTS

Stimulation of PKC using phorbol 12-myristate-13-acetate (PMA) activated the hK(2P) 18.1 current by 3.1-fold in a concentration-dependent fashion. The inactive analogue 4α-PMA had no effect on channel activity. The specific PKC inhibitors bisindolylmaleimide I, Ro-32-0432 and chelerythrine reduced PMA-induced channel activation indicating that PKC is involved in this effect of PMA. Selective activation of conventional PKC isoforms with thymeleatoxin (100 nM) did not reproduce K(2P) 18.1 channel activation. Current activation by PMA was not affected by pretreatment with CsA (calcineurin inhibitor) or KT 5720 (PKA inhibitor), ruling out a significant contribution of calcineurin or cross-talk with PKA to the PKC-dependent hK(2P) 18.1 activation. Finally, mutation of putative PKC phosphorylation sites did not prevent PMA-induced K(2P) 18.1 channel activation.

CONCLUSIONS AND IMPLICATIONS

We demonstrated that activation of hK(2P) 18.1 (TRESK) by PMA is mediated by PKC stimulation. Hence, PKC-mediated activation of K(2P) 18.1 background currents may serve as a novel molecular target for migraine treatment.

Alkamid database: Chemistry, occurrence and functionality of plant N-alkylamides

ETHNOPHARMACOLOGICAL RELEVANCE

N-Alkylamides (NAAs) are a promising group of bioactive compounds, which are anticipated to act as important lead compounds for plant protection and biocidal products, functional food, cosmeceuticals and drugs in the next decennia. These molecules, currently found in more than 25 plant families and with a wide structural diversity, exert a variety of biological-pharmacological effects and are of high ethnopharmacological importance. However, information is scattered in literature, with different, often unstandardized, pharmacological methodologies being used. Therefore, a comprehensive NAA database (acronym: Alkamid) was constructed to collect the available structural and functional NAA data, linked to their occurrence in plants (family, tribe, species, genus).

MATERIALS AND METHODS

For loading information in the database, literature data was gathered over the period 1950-2010, by using several search engines. In order to represent the collected information about NAAs, the plants in which they occur and the functionalities for which they have been examined, a relational database is constructed and implemented on a MySQL back-end.

RESULTS

The database is supported by describing the NAA plant-, functional- and chemical-space. The chemical space includes a NAA classification, according to their fatty acid and amine structures.

CONCLUSIONS

The Alkamid database (publicly available on the website http://alkamid.ugent.be/) is not only a central information point, but can also function as a useful tool to prioritize the NAA choice in the evaluation of their functionality, to perform data mining leading to quantitative structure-property relationships (QSPRs), functionality comparisons, clustering, plant biochemistry and taxonomic evaluations.

The acid-sensitive, anesthetic-activated potassium leak channel, KCNK3, is regulated by 14-3-3β-dependent, protein kinase C (PKC)-mediated endocytic trafficking

The acid-sensitive neuronal potassium leak channel, KCNK3, is vital for setting the resting membrane potential and is the primary target for volatile anesthetics. Recent reports demonstrate that KCNK3 activity is down-regulated by PKC; however, the mechanisms responsible for PKC-induced KCNK3 down-regulation are undefined. Here, we report that endocytic trafficking dynamically regulates KCNK3 activity. Phorbol esters and Group I metabotropic glutamate receptor (mGluR) activation acutely decreased both native and recombinant KCNK3 currents with concomitant KCNK3 surface losses in cerebellar granule neurons and cell lines. PKC-mediated KCNK3 internalization required the presence of both 14-3-3β and a novel potassium channel endocytic motif, because depleting either 14-3-3β protein levels or ablating the endocytic motif completely abrogated PKC-regulated KCNK3 trafficking. These results demonstrate that neuronal potassium leak channels are not static membrane residents but are subject to 14-3-3β-dependent regulated trafficking, providing a straightforward mechanism to modulate neuronal excitability and synaptic plasticity by Group I mGluRs.

Activation of oral trigeminal neurons by fatty acids is dependent upon intracellular calcium

The chemoreception of dietary fat in the oral cavity has largely been attributed to activation of the somatosensory system that conveys the textural properties of fat. However, the ability of fatty acids, which are believed to represent the proximate stimulus for fat taste, to stimulate rat trigeminal neurons has remained unexplored. Here, we found that several free fatty acids are capable of activating trigeminal neurons with different kinetics. Further, a polyunsaturated fatty acid, linoleic acid (LA), activates trigeminal neurons by increasing intracellular calcium concentration and generating depolarizing receptor potentials. Ion substitution and pharmacological approaches reveal that intracellular calcium store depletion is crucial for LA-induced signaling in a subset of trigeminal neurons. Using pseudorabies virus (PrV) as a live cell tracer, we identified a subset of lingual nerve-innervated trigeminal neurons that respond to different subsets of fatty acids. Quantitative real-time PCR of several transient receptor potential channel markers in individual neurons validated that PrV labeled a subset but not the entire population of lingual-innervated trigeminal neurons. We further confirmed that the LA-induced intracellular calcium rise is exclusively coming from the release of calcium stores from the endoplasmic reticulum in this subset of lingual nerve-innervated trigeminal neurons.

Gustatory, trigeminal, and olfactory aspects of nicotine intake in three mouse strains

Studies of nicotine consumption in rodents often intend to investigate nicotine's post-absorptive effects, yet little is known about the pre-absorptive sensory experience of nicotine drinking, including gustatory, trigeminal, and olfactory influences. We conditioned taste aversion (CTA) to nicotine in males of 3 inbred mouse strains: C57BL/6J, DBA/2J, and 129X1/SvJ by repeatedly pairing 150 μg/ml nicotine drinking with lithium chloride injections. Generalization to a variety of bitter, sour, sweet, salty, and irritant solutions and to nicotine odor was then examined. Nicotine CTA generalized to the bitter stimulus quinine hydrochloride and the chemosensory irritant spilanthol in all strains. It also showed strain specificity, generalizing to hydrogen peroxide (an activator of TRPA1) in C57BL/6J mice and to the olfactory cue of nicotine in DBA/2J mice. These behavioral assays demonstrate that the sensory properties of nicotine are complex and include multiple gustatory, irritant, and olfactory components. How these qualities combine at the level of perception remains to be assessed, but sensory factors clearly exert an important influence on nicotine ingestion and their contribution to net intake of nicotine should not be neglected in animal or human studies.

TRESK: the lone ranger of two-pore domain potassium channels

TRESK (TWIK-related spinal cord K(+) channel, KCNK18) belongs to the two-pore domain (K2P) background (leak) potassium channel family. Unlike other K2P channels, TRESK is activated by the calcium signal in heterologous expression systems. The activation is mediated by the calcium/calmodulin-dependent protein phosphatase, calcineurin. TRESK is abundantly expressed in dorsal root and trigeminal ganglia. The active ingredient of Sichuan pepper, sanshool, has been suggested to evoke tingling paresthesia by inhibiting the channel in a mechanoreceptor subpopulation of sensory neurons. Recently, dominant-negative mutation of human TRESK was found to be linked to migraine with aura in a large pedigree. It is hoped that future TRESK agonists may prevent or ameliorate the debilitating symptoms of migraine. It will be interesting to see whether the calcineurin-activated K(+) channel maintains normal excitability in the cerebral cortex thereby arresting cortical spreading depression (CSD), or prevents migraine attack only in the trigeminovascular (TGVS) system.