Deletion of vanilloid receptor (TRPV1) in mice alters behavioral effects of ethanol

The vanilloid receptor TRPV1 is activated by ethanol and this may be important for some of the central and peripheral actions of ethanol. To determine if this receptor has a role in ethanol-mediated behaviors, we studied null mutant mice in which the Trpv1 gene was deleted. Mice lacking this gene showed significantly higher preference for ethanol and consumed more ethanol in a two-bottle choice test as compared with wild type littermates. Null mutant mice showed shorter duration of loss of righting reflex induced by low doses of ethanol (3.2 and 3.4 g/kg) and faster recovery from motor incoordination induced by ethanol (2 g/kg). However, there were no differences between null mutant and wild type mice in severity of ethanol-induced acute withdrawal (4 g/kg) or conditioned taste aversion to ethanol (2.5 g/kg). Two behavioral phenotypes (decreased sensitivity to ethanol-induced sedation and faster recovery from ethanol-induced motor incoordination) seen in null mutant mice were reproduced in wild type mice by injection of a TRPV1 antagonist, capsazepine (10 mg/kg). These two ethanol behaviors were changed in the opposite direction after injection of capsaicin, a selective TRPV1 agonist, in wild type mice. The studies provide the first evidence that TRPV1 is important for specific behavioral actions of ethanol.     

TRPV1 (vanilloid receptor) in the urinary tract: expression, function and clinical applications

The transient receptor potential vanilloid subfamily 1 (TRPV1) is an ion channel activated by capsaicin, heat, protons and endogenous ligands such as anandamide. It is largely expressed in the urinary tract of mammals. Structures in which the receptor expression is firmly established include sensory fibers and urothelial cells, although the presence of TRPV1 in other cell types has been reported. As in other systems, pain perception was the first role attributed to TRPV1 in the urinary tract. However, it is now increasingly clear that TRPV1 also regulates the frequency of bladder reflex contractions, either through direct excitation of sensory fibers or through urothelial-sensory fiber cross talk involving the release of neuromediators from the epithelial cells. In addition, the recent identification of the receptor in urothelial and prostatic cancer cells raise the exciting hypothesis that TRPV1 is involved in cell differentiation. Desensitization of the receptor by capsaicin and resiniferatoxin has been investigated for therapeutic purposes. For the moment, lower urinary tract dysfunctions in which some benefit was obtained include painful bladder syndrome and overactive bladder of neurogenic and non-neurogenic origin. However, desensitization may become obsolete when non-toxic, potent TRPV1 antagonists become available.     

Identification and characterisation of SB-366791, a potent and selective vanilloid receptor (VR1/TRPV1) antagonist

Vanilloid receptor-1 (TRPV1) is a non-selective cation channel, predominantly expressed by peripheral sensory neurones, which is known to play a key role in the detection of noxious painful stimuli, such as capsaicin, acid and heat. To date, a number of antagonists have been used to study the physiological role of TRPV1; however, antagonists such as capsazepine are somewhat compromised by non-selective actions at other receptors and apparent modality-specific properties. SB-366791 is a novel, potent, and selective, cinnamide TRPV1 antagonist isolated via high-throughput screening of a large chemical library. In a FLIPR-based Ca(2+)-assay, SB-366791 produced a concentration-dependent inhibition of the response to capsaicin with an apparent pK(b) of 7.74 +/- 0.08. Schild analysis indicated a competitive mechanism of action with a pA2 of 7.71. In electrophysiological experiments, SB-366791 was demonstrated to be an effective antagonist of hTRPV1 when activated by different modalities, such as capsaicin, acid or noxious heat (50 degrees C). Unlike capsazepine, SB-366791 was also an effective antagonist vs. the acid-mediated activation of rTRPV1. With the aim of defining a useful tool compound, we also profiled SB-366791 in a wide range of selectivity assays. SB-366791 had a good selectivity profile exhibiting little or no effect in a panel of 47 binding assays (containing a wide range of G-protein-coupled receptors and ion channels) and a number of electrophysiological assays including hippocampal synaptic transmission and action potential firing of locus coeruleus or dorsal raphe neurones. Furthermore, unlike capsazepine, SB-366791 had no effect on either the hyperpolarisation-activated current (I(h)) or Voltage-gated Ca(2+)-channels (VGCC) in cultured rodent sensory neurones. In summary, SB-366791 is a new TRPV1 antagonist with high potency and an improved selectivity profile with respect to other commonly used TRPV1 antagonists. SB-366791 may therefore prove to be a useful tool to further study the biology of TRPV1.     

Oxidizing reagent copper-o-phenanthroline is an open channel blocker of the vanilloid receptor TRPV1

The TRPV1 channel plays an important role in generating nociceptive signals in mammalian primary sensory neurons. It consists of 838 amino acids with six transmembrane segments (TM1-TM6), a pore-forming loop between TM5 and TM6 and N- and C- terminals located intracellularly. It is a homotetramer and forms a nonselective cationic channel that can be opened by capsaicin, weak acids and noxious heat. There are 18 cysteines (Cys), three of which are located on the extracellular side of the receptor in and around the region of the pore-forming loop. We report that the TRPV1 channel in transfected HEK293T cells and in cultured rat DRG neurons is blocked in the open state by an oxidizing agent Cu-o-phenanthroline complex (Cu:Phe). The effects of Cu:Phe are concentration dependent ( IC50 = 5.2 : 20.8 microm ) and fully reversible. Cu:Phe applied immediately before exposure to an acidic solution, capsaicin or noxious heat is without effect. Substitutions of the extracellular Cys residues (616, 621, 634) by glycine individually or together do not alter the blocking effects of Cu:Phe suggesting that disulfide cross-linking does not represent the underlying mechanism. It is suggested that the complex Cu:Phe, a bulky, positively charged molecule, represents a very effective and reversible open channel blocker of TRPV1.     

Effect of olvanil on the afferent and efferent function of capsaicin-sensitive C-fibers in guinea pig airways

The aim of the present study was to examine the ability of the nonpungent vanilloid VR1 receptor agonist, olvanil, to activate the afferent and efferent function of capsaicin-sensitive C-fibers in guinea pig airways. We found that while capsaicin (10 nM-10 microM) and resiniferatoxin (0.1 nM-1.0 microM) evoked a robust contraction of the guinea pig trachea in vitro, olvanil (10 nM-10 microM) was a weak spasmogen. In addition, pretreatment with olvanil caused only a minor reduction of subsequent responses to capsaicin or resiniferatoxin. Using single fiber recording from guinea pig airway C-fibers, we found that olvanil (10 microM) did not evoke action potential discharge although these fibers responded vigorously to capsaicin after prolonged treatment with olvanil (10 microM). These findings are indicative of significant differences in the relative sensitivity of vanilloid VR1 receptor-transfected cells and the peripheral terminals of airway C-fibers to pungent and nonpungent vanilloid VR1 receptor agonists.     

TRPV1 and the gut: from a tasty receptor for a painful vanilloid to a key player in hyperalgesia

Capsaicin, the pungent ingredient in red pepper, has been used since ancient times as a spice, despite the burning sensation associated with its intake. More than 50 years ago, Nikolaus Jancsó discovered that capsaicin can selectively stimulate nociceptive primary afferent neurons. The ensuing research established that the neuropharmacological properties of capsaicin are due to its activation of the transient receptor potential ion channel of the vanilloid type 1 (TRPV1). Expressed by primary afferent neurons innervating the gut and other organs, TRPV1 is gated not only by vanilloids such as capsaicin, but also by noxious heat, acidosis and intracellular lipid mediators such as anandamide and lipoxygenase products. Importantly, TRPV1 can be sensitized by acidosis and activation of various pro-algesic pathways. Upregulation of TRPV1 in inflammatory bowel disease and the beneficial effect of TRPV1 downregulation in functional dyspepsia and irritable bladder make this polymodal nociceptor an attractive target of novel therapies for chronic abdominal pain.     

Role of neuropeptide receptor systems in vanilloid VR1 receptor-mediated gastric acid secretion in rat brain

Previously, we reported that the injection of capsaicin into the lateral cerebroventricle (i.c.v.) stimulated gastric acid secretion via vanilloid VR1 receptors and the vagal cholinergic pathways in anesthetized rats. In the present study, we investigated the involvement of receptor systems for neurokinin A, calcitonin gene-related peptide (CGRP) and glutamate in the vanilloid VR1 receptor-mediated response. The i.c.v. injection of neurokinin A (30 nmol) stimulated gastric acid secretion in the presence of cis-2-(diphenylmethyl)-N-[(2-iodophenyl)methyl]-1-azabicyclo[2.2.2]octan-3-amine oxalate (L-703606, a tachykinin NK1 receptor antagonist, 30 nmol) and the effect was inhibited by cyclo[Gln-Trp-Phe-Gly-Leu-Met] (L-659877, a tachykinin NK2 receptor antagonist, 30 nmol); the values were 145.9 +/- 32.3 and 21.1 +/- 16.6 microEq HCl per 120 min, respectively. The value in the control group was 14.3 +/- 3.8 microEq HCl. The tachykinin NK2 receptor-mediated secretion was inhibited by i.c.v. injections of antagonists of the CGRP1 receptor (human CGRP fragment 8-37, 15 nmol) and non-N-methyl-D-aspartate (non-NMDA)-type glutamate receptor (6-cyano-7-nitroquinoxaline-2,3-dione, 10.9 nmol); the values were 30.8+/-29.8 and 5.7+/-16.9 microEq HCl, respectively. Gastric acid secretion induced by the i.c.v. injection of 30 nmol capsaicin (178.4 +/- 34.0 microEq HCl) was inhibited by antagonists of tachykinin NK2 (23.7 +/- 6.2) and CGRP1 (21.2 +/- 8.5), but not tachykinin NK1 (181.4 +/- 37.0), receptors. The gastric acid secretion induced by capsaicin was decreased by the i.c.v. pre-injection of low doses of neurokinin A or CGRP, which alone had no effect on the secretion. These findings suggest the involvement of tachykinin NK2, CGRP and non-NMDA receptor systems in the vanilloid VR1 receptor-mediated regulation of gastric acid secretion in the rat brain regions close to the lateral cerebroventricle.     

Cloning and functional characterization of dog transient receptor potential vanilloid receptor-1 (TRPV1)

Transient receptor potential vanilloid receptor-1 (TRPV1) is a sensory neuron-specific cation channel capable of integrating various noxious chemical and physical stimuli. The dog orthologue of TRPV1 was cloned using cDNA from nodose ganglia and heterologously expressed in HEK293(OFF) cells. At the amino acid level, dTRPV1 displays 85-89% sequence identity to other TRPV1 orthologues. Molecular pharmacological characterization of HEK293(OFF) cells expressing TRPV1 was assessed using a fluorescence imaging plate reader (FLIPR)-based calcium imaging assay. Dog TRPV1 was activated by various known TRPV1 agonists in a concentration-dependent manner: Ag23 = resiniferatoxin > olvanil approximately arvanil > capsaicin > phorbol 12-phenylacetate 13-acetate 20-homovanillate (PPAHV) > N-oleoyldopamine (OLDA). In addition, select TRPV1 antagonists (capsazepine, I-resiniferatoxin and N-(-4-tertiarybutylphenyl)-4-(3-cholorpyridin-2-yl)tetrahydropyrazine-1(2H)-carbox-amide (BCTC)) were able to block the response of dTRPV1 to capsaicin. Furthermore, the dog TRPV1 lacked a conserved protein kinase A (PKA) phosphorylation site (117) found in other cloned orthologues, which may have physiological consequences on dog TRPV1 function. Taken together, these data constitute the first study of the cloning, expression and pharmacological characterization of dog TRPV1.     

The endogenous cannabinoid anandamide activates vanilloid receptors in the rat hippocampal slice

We have previously reported that the synthetic cannabinoid receptor agonist WIN55,212-2 causes a selective reduction in paired-pulse depression of population spikes in the CA1 region of the rat hippocampal slice. This effect is consistent with the observation that activation of cannabinoid receptors inhibits GABA release in the hippocampus. We have now investigated the actions of the putative endogenous cannabinoids 2-arachidonoyl-glycerol (2-AG) and anandamide in this system. 2-AG mimicked the effect of WIN55,212-2 by selectively reducing paired-pulse depression at concentrations of 1–30 μM. In contrast, anandamide caused a selective increase in paired-pulse depression at concentrations of 1–30 μM. This effect was mimicked by the vanilloid receptor agonists capsaicin and resiniferatoxin, and blocked by the vanilloid receptor antagonist capsazepine, but not by the cannabinoid receptor antagonist AM281. These results are the first to demonstrate a clear functional vanilloid receptor-mediated effect in the hippocampus, and further, that anandamide but not 2-AG acts at these receptors to increase paired-pulse depression of population spikes.     

Transient receptor potential vanilloid 1 agonists modulate hippocampal CA1 LTP via the GABAergic system

Transient receptor potential vanilloid 1 (TRPV1) was shown to modulate hippocampal CA1 pyramidal cell synaptic plasticity, including long-term potentiation (LTP) and long-term depression (LTD). Synaptic plasticity is the cellular mechanism thought to mediate declarative learning and memory in the hippocampus. Although TRPV1 is involved in modulating hippocampal plasticity, it has yet to be determined how TRPV1 mediates its effects. Using field electrophysiology in hippocampal CA1 stratum radiatum we investigated how TRPV1 agonists modulate LTP, low frequency stimulation-induced LTD, and (RS)-3,5-dihydroxyphenylglycine (DHPG)-induced LTD. First we confirmed that TRPV1 agonists induce enhancement of CA1 pyramidal cell LTP in the absence the GABA_A receptor antagonist picrotoxin. Because it was recently determined that TRPV1 mediates a novel form of LTD in CA1 inhibitory GABAergic interneurons, which can disinhibit CA1 pyramidal cells, we used picrotoxin to block the effect of the GABAergic circuitry on CA1 LTP. When using picrotoxin, the TRPV1 agonist-induced enhancement of CA1 LTP was eliminated suggesting that the GABAergic circuitry is required for TRPV1 agonist mediated increases. Regarding LTD, in contrast to previously reported data, we did not see TRPV1 agonist-mediated effect on low frequency-induced stimulus LTD. However, during DHPG-induced LTD, TRPV1 was involved in the acute, but not the long-term depression phase of this plasticity. In summary, our findings support TRPV1 agonist involvement in hippocampal synaptic plasticity, including its enhancement of CA1 LTP. We demonstrate that the enhancement mediated by TRPV1 agonists requires GABA input to pyramidal cells thus providing a mechanism for how TRPV1 agonists modulate hippocampal synaptic plasticity.     

Capsazepine, a vanilloid receptor antagonist, inhibits allergen-induced tracheal contraction

To investigate the possible role of the vanilloid receptor-1 (TRPV1) in allergic airway responses, the effect of the specific TRPV1 receptor antagonist capsazepine was examined. Capsazepine significantly decreased the ovalbumin-induced contraction of isolated tracheal rings from ovalbumin-sensitized guinea pigs. This is the first report directly showing the involvement of the TRPV1 in experimental allergic airway responses.     

Decreased pain sensitivity of Capsaicin-treated rats results from decreased VR1 expression

We investigated the neurotoxic effects of capsaicin (CAP) on pain sensitivity and on the expression of capsaicin receptor, the vanilloid receptor (VR1), in rats. High-dose application of CAP has been known to degenerate a large fraction of the sensory neurons. Although the neurotoxic effects of CAP are well documented, the effects of CAP on the vanilloid receptor (VR1) are not yet known. In this paper, we investigated the effects of high-dose application of CAP on the expression of VR1 in rats. Thermal and mechanical pain sensitivity was reduced when neonatal rats were treated with a high dose of CAP. This reduction of pain sensitivity was significantly decreased after initiating carrageenan-induced inflammation. The expression of VR1 in dorsal root ganglia (DRG) isolated from the CAP-treated rats was reduced compared to that from the vehicle-treated rats. Therefore, we can conclude that the neurotoxic effect of CAP is related to the decrease of VR1 expression.     

Cloning and pharmacological characterization of the guinea pig P2X7 receptor orthologue

BACKGROUND AND PURPOSE: The human, rat, and mouse P2X(7) receptors have been previously characterized, and in this study we report the cloning and pharmacological properties of the guinea pig orthologue. EXPERIMENTAL APPROACH: A cDNA encoding for the guinea pig P2X(7) receptor was isolated from a guinea pig brain library. The receptor was expressed in U-2 OS cells using the BacMam viral expression system. A monoclonal antibody was used to confirm high levels of cell surface expression and the functional properties were determined in ethidium bromide accumulation studies. KEY RESULTS: The predicted guinea pig protein is one amino acid shorter than the human and rat orthologues and over 70% identical to the rat and human receptors. In contrast to human and rat P2X(7) receptors, 2'-&3'-O-(4benzoylbenzoyl)ATP (BzATP) was a partial agonist of the guinea pig P2X(7) receptor when compared to ATP and acted as an antagonist in some assays. However, as at other species orthologues, BzATP was more potent than ATP. The guinea pig P2X(7) receptor possessed higher affinity for 1-[N,O-bis(5-isoquinoline sulphonyl)-N-methyl-L-tyrosyl]-4-phenylpiperazine (KN62), suramin and Coomassie Brilliant Blue than human or rat P2X(7) receptors suggesting that it is pharmacologically different to other rodent or human P2X(7) receptors. CONCLUSIONS AND IMPLICATIONS: The guinea pig recombinant P2X(7) receptor displays a number of unique properties that differentiate it from the human, rat and mouse orthologues and this structural and functional information should aid in our understanding of the interaction of agonists and antagonist with the P2X(7) receptor.     

Novel agonistic action of mustard oil on recombinant and endogenous porcine transient receptor potential V1 (pTRPV1) channels

Neurogenic components play a crucial role in inflammation and nociception. Mustard oil (MO) is a pungent plant extract from mustard seed, horseradish and wasabi, the main constituent of which is allylisothiocyanate. We have characterized the action of MO on transient receptor potential V1 (TRPV1), a key receptor of signal transduction pathways in the nociceptive system, using fura-2-based [Ca(2+)](i) imaging and the patch-clamp technique in a heterologous expression system and sensory neurons. In human embryonic kidney (HEK) 293 cells expressing porcine TRPV1 (pTRPV1), MO evoked increases of [Ca(2+)](i) in a concentration-dependent manner. A high concentration of MO elicited irreversible cell swelling. Capsazepine, ruthenium red and iodoresiniferatoxin dose-dependently suppressed the MO-induced [Ca(2+)](i) increase. MO elicited outward rectified currents in pTRPV1-expressing HEK 293 cells with a reversal potential similar to that of capsaicin. [Ca(2+)](i) responses to MO were completely abolished by the removal of external Ca(2+). MO simultaneously elicited an inward current and increase of [Ca(2+)](i) in the same cells, indicating that MO promoted Ca(2+) influx through TRPV1 channels. In cultured porcine dorsal root ganglion (DRG) neurons, MO elicited a [Ca(2+)](i) increase and inward current. Among DRG neurons responding to MO, 85% were also sensitive to capsaicin. The present data indicate that MO is a novel agonist of TRPV1 channels, and suggest that the action of MO in vivo may be partly mediated via TRPV1. These results provide an insight into the TRPV1-mediated effects of MO on inflammation and hyperalgesia.     

Expression of vanilloid receptors in rat gastric epithelial cells: role in cellular protection

Vanilloid receptors subtype 1 (VR1), a nonselective cation channel responsive to capsaicin, protons, and noxious heat, has been recently identified in not only neural but also non-neural cells. In the present study, we demonstrated the peripheral expression of VR1 in gastric mucosal epithelial cells and investigated the role of the receptor in cellular protection. The rat gastric mucosal epithelial cell line was used. The expression of VR1 was examined by Western blotting and RT-PCR. Cell damage was induced by immersion in 10% ethanol or acid (pH 4.0) for 30 min, and cell viability was determined by MTT assay. Capsaicin or resiniferatoxin was added 30 min before the challenge with ethanol or acid, while capsazepine or ruthenium red (a VR1 antagonist) was added simultaneously with capsaicin. The distinct expression of VR1 protein and mRNA was detected in rat gastric mucosal epithelial cell line as well as in the rat stomach and spinal cord by Western blotting and RT-PCR, respectively. The cDNA sequence of the PCR product was found to be almost identical to that of the authentic VR1 (99.8%) when the product was subcloned and sequenced. On the other hand, the cell damage induced by ethanol or acid was dose-dependently prevented by pretreatment with capsaicin. The protective effect of capsaicin was mimicked by resiniferatoxin and almost totally abolished by co-addition of capsazepine or ruthenium red. These findings suggest that VR1 is expressed peripherally in gastric mucosal epithelial cells and plays a cellular protective role.     

Evidence for the involvement of vanilloid receptor in the antinociception produced by the dialdeydes unsaturated sesquiterpenes polygodial and drimanial in rats

This study investigated whether or not the neonatal treatment of rats with the sesquiterpenes polygodial or drimanial could cause persistent antinociception similar to that induced by capsaicin. Rats were injected subcutaneously 48 h after birth with capsaicin (50 mg/kg), polygodial (150 mg/kg), drimanial (150 mg/kg) or vehicle (1ml/kg). Six to eight weeks later, rats were tested in models of nociception. Treatment of rats with capsaicin, polygodial or drimanial produced significant inhibition of the first phase and, to a lesser extent, the second phase of formalin-induced nociception. A significant reduction in Complete Freund's Adjuvant and capsaicin-induced hyperalgesia was observed in the animals neonatally treated with capsaicin, polygodial or drimanial compared with vehicle-treated rats. Moreover, both sesquiterpenes caused inhibition of plasma extravasation induced by injection of capsaicin. The neonatal treatment with capsaicin, polygodial or drimanial significantly decreased [3H]-resiniferatoxin binding sites in the rat spinal cord, but only capsaicin neonatal treatment significantly reduced the expression of TRPV1 in dorsal root ganglia (DRG) when assessed by Western blot. These results extend our previous findings demonstrating that the neonatal treatment of rats with polygodial or drimanial, similar to that reported for capsaicin, produced persistent antinociception in adult animals associated with TRPV1 down-regulation in the spinal cord, but not TRPV1 expression in DRG.     

辣椒素受体研究进展

辣椒素受体（vanilloid receptor subtypel，VR1）是机体的一个重要的伤害性感受分子，除了参与中枢和外周水平疼痛的形成外，还参与了多种生理活动和病理过程。激活神经纤维末端的辣椒素受体，可调节外周血管的舒缩，影响血压；对缺血心肌起到保护作用；辣椒素受体还参与哮喘的发生，调节胃酸的分泌，促进胃肠蠕动。另外，激活辣椒素受体，还可抑制毛干的增殖，并介导肿瘤细胞的凋亡。本文主要就辣椒素受体近几年的研究情况作一简要综述。     

Molecular cloning and pharmacological characterization of the guinea pig 5-HT1E receptor

The human 5-HT(1E) receptor gene was cloned more than a decade ago. Little is known about its function, and there have been no reports of its existence in the genome of small laboratory animals. In this study, attempts to clone the 5-HT(1E) gene from the rat and mouse were unsuccessful. In fact, a search of the mouse genome database revealed that the 5-HT(1E) receptor gene is missing from the mouse genome. However, the 5-HT(1E) gene was cloned from guinea pig genomic DNA and was characterized. The guinea pig 5-HT(1E) receptor gene encodes a protein of 365 amino acids. It shares 88% (nucleic acid) and 95% (amino acid) homology with the human receptor. The guinea pig 5-HT(1E) receptor showed similar pharmacology to the human 5-HT(1E) receptor in radioligand binding assays. Serotonin (5-hydroxytryptamine, 5-HT) dose-dependently stimulated [35S]GTPgammaS binding to the guinea pig 5-HT(1E) receptor with an EC(50) of 13.6+/-1.92 nM, similar to that of the human 5-HT(1E) receptor (13.7+/-1.78 nM). Activation of the guinea pig 5-HT(1E) receptor was also achieved by ergonovine, alpha-methyl-5-HT, 1-naphthylpiperazine, methysergide, tryptamine, and 1-(2,5-dimethoxy-4-iodophenyl)-2-aminopropane (DOI). Methiothepin exhibited antagonist activity. Quantitative real-time polymerase chain reaction (qRT-PCR) analysis showed that 5-HT(1E) mRNA was present in the guinea pig brain with the greatest abundance in the hippocampus, followed by the olfactory bulb. Lower levels were detected in the cortex, thalamus, pons, hypothalamus, midbrain, striatum, and cerebellum. Our current study marks the first identification of the 5-HT(1E) receptor gene in a commonly used laboratory animal species. This finding should allow the elucidation of the receptor's role(s) in the complex coordination of central serotonergic effects.     

The role of the vanilloid (capsaicin) receptor (TRPV1) in physiology and pathology

The cloning of the vanilloid receptor 1 opened a floodgate for discoveries regarding the function of this complex molecule. It has been found that, in addition to heat, protons and vanilloids, this receptor also responds to various endogenous ligands. Furthermore, it has been also emerged that, through associations with other molecules, the vanilloid receptor 1 plays an important role in the integration of various stimuli and modulation of cellular excitability. Although, originally, the vanilloid receptor 1 was associated with nociceptive primary afferent fibres, it has been gradually revealed that it is broadly expressed in the brain, epidermis and visceral cells. The expression pattern of the vanilloid receptor 1 indicates that it could be involved in various physiological functions and in the pathomechanisms of diverse diseases. Here, we summarise the molecular, pharmacological and physiological characteristics, and putative functions, of the vanilloid receptor 1, and discuss the therapeutic potential of this molecule.     

Differential modulation of agonist and antagonist structure activity relations for rat TRPV1 by cyclosporin A and other protein phosphatase inhibitors

The transient receptor potential V1 channel (vanilloid receptor, TRPV1) represents a promising therapeutic target for inflammatory pain and other conditions involving C-fiber sensory afferent neurons. Sensitivity of TRPV1 is known to be subject to modulation by numerous signaling pathways, in particular by phosphorylation, and we wished to determine whether TRPV1 structure activity relations could be differentially affected. We demonstrate here that the structure activity relations of TRPV1, as determined by ⁴⁵Ca² uptake, were substantially altered by treatment of the cells with cyclosporin A, an inhibitor of protein phosphatase 2B. Whereas the potency of resiniferatoxin for stimulation of ⁴⁵Ca² was not altered by cyclosporin A treatment, the potencies of some other agonists were increased up to 8-fold. Among the antagonists examined, potencies were reduced to a lesser extent, ranging from 1- to 2.5-fold. Finally, the efficacy of partial agonists was increased. In contrast to cyclosporin A, okadaic acid, an inhibitor of protein phosphatases 1 and 2A, had little effect on agonist potencies, and calyculin A, an inhibitor of protein phosphatases 1 and 2A but with somewhat different selectivity from that of okadaic acid, caused changes in structure activity relations distinct from those induced by cyclosporin A. Because phosphatase activity differentially modulates the structure activity relations of TRPV1 agonists and antagonists, our findings predict that it may be possible to design agonists and antagonists selective for TRPV1 in a specific regulatory environment. A further implication is that it may be desirable to tailor screening approaches for drug discovery to reflect the desired regulatory state of the targeted TRPV1.