Role Of Transient Receptor Potential Research Articles

Trpc3-Mediated Electrical Remodeling of Cardiac Myocytes

Recent evidence suggests a key role of transient receptor potential (TRP) channels in cardiac pathophysiology with TRPC3 as one potential key player in cardiac remodeling. TRPC3 is typically up-regulated by hypertrophic stimuli and may be involved in distorted Ca2+ signaling that drives pathological remodeling. As TRPC proteins generate non-selective cation conductances, we hypothesized that these channels may not only govern Ca2+-mediated gene expression but exert in addition a severe impact on basic electrical properties and excitability of the myocardium. Utilizing the patch clamp technique we characterized membrane currents and electrical properties of cardiomyocytes in response to enhanced TRPC3 expression in the murine HL-1 model. Stimulation of TRPC3-overexpressing HL-1 cells with endothelin-1 [100 nM] (ET-1) as a Gqi-PLC-activator gave rise to a conductance with features distinctly different from the properties described for TRPC3 conductance in expression systems. In HL-1 cells, the TRPC3 over-expression-induced conductance in physiological solutions reversed at about −50 mV, displayed profound outward rectification and was suppressed by the TRPC3-inhibitor Pyr3 [10 µM] (ethyl-1-(4-(2,3,3-trichloroacrylamide)phenyl)-5-(trifluoromethyl)-1H-pyrazole-4-carboxylate). As a result of this conductance, action potential duration was effectively shortened by ET-1 in HL-1 myocytes over-expressing the TRPC3, while this effect was minute in wild-type myocytes. Moreover, TRPC3 over-expression enabled significant depolarizing effects of ET-1 along with action potential shortening and reduction of refractory period. Our results suggests that increased expression of TRPC3 in cardiomyocytes may significantly contribute to electrical remodeling in hypertrophic hearts, generating changes in action potential morphology that are likely to promote arrhythmias.

Effects of transient receptor potential (TRP) channel agonists and antagonists on slowly adapting type II mechanoreceptors in the rat sinus hair follicle

The possible functional role of transient receptor potential (TRP) channels was investigated by testing various TRP agonists and antagonists in an isolated rat sinus hair follicle preparation. Extracellular recordings from slowly adapting type II mechanoreceptor units were made. The antagonist capsazepine depressed spontaneous and mechanically evoked activity, with an IC(50) of 82 microM. In one-third of units, capsazepine caused a selective depression of mechanically evoked firing, such that the existing spontaneous firing was interrupted by an absence of activity during the mechanical stimulus. The broad spectrum TRP blocker ruthenium red (30 microM) had inconsistent effects, although in some units a delayed onset (following wash) bursting and paroxysmal firing ensued. The agonist icilin (50-100 microM) had an excitatory effect on spontaneous firing, and (-)-menthol (200 microM) had inconsistent effects. Cinnamaldehyde (1-2 mM) depressed all types of activity equally, mechanically evoked and spontaneous. Camphor (0.5-2 mM) also depressed all types of activity, although it had a preferential effect on spontaneous activity. Capsaicin (1-10 microM) and allyl isothiocyanate (50-100 microM) had no clear effects. These results rule out any role for TRPA1 and TRPV1 channels in mechanotransduction processes of slowly adapting type II mechanoreceptors.

A Double TRPtych: Six Views of Transient Receptor Potential Channels in Disease and Health: Table 1.

At the 2008 Annual Meeting of the Society for Neuroscience, a Mini-Symposium entitled "Contributions to TRP Channels to Neurological Disease" included talks from six heads of newly established laboratories, each with a unique research focus, model system, and set of experimental tools. Some of the questions addressed in these talks include the following. What is the role of transient receptor potential (TRP) channels in pain perception? How do normally functioning TRP channels contribute to cell death pathways? What are the characteristics of TRPpathies, disease states that result from overactive or underactive TRP channels? How are TRP channels regulated by signal transduction cascades? This review summarizes recent results from those laboratories and provides six perspectives on the subject of TRP channels and disease.

TRPV1 receptors on unmyelinated C‐fibres mediate colitis‐induced sensitization of pelvic afferent nerve fibres in rats

Patients with inflammatory bowel disease often suffer from gastrointestinal motility and sensitivity disorders. The aim of the current study was to investigate the role of transient receptor potential of the vanilloid type 1 (TRPV1) receptors in the pathophysiology of colitis-induced pelvic afferent nerve sensitization. Trinitrobenzene sulphate (TNBS) colitis (7.5 mg, 30% ethanol) was induced in Wistar rats 72 h prior to the experiment. Single-fibre recordings were made from pelvic nerve afferents in the decentralized S1 dorsal root. Fibres responding to colorectal distension (CRD) were identified in controls and rats with TNBS colitis. The effect of the TRPV1 antagonist N-(4-tertiarybutylphenyl)-4-(3-chlorophyridin-2-yl)tetrahydropyrazine-1(2H)carboxamide (BCTC; 0.25-5 mg kg(-1)) or its vehicle (hydroxypropyl-beta-cyclodextrin) was tested on the afferent response to repetitive distensions (60 mmHg). Immunocytochemical staining of TRPV1 and NF200, a marker for A-fibre neurons, was performed in the dorsal root ganglia L6-S1. TNBS colitis significantly increased the response to colorectal distension of pelvic afferent C-fibres. BCTC did not significantly affect the C-fibre response in controls, but normalized the sensitized response in rats with colitis. TNBS colitis increased the spontaneous activity of C-fibres, an effect which was insensitive to administration of BCTC. TNBS colitis had no effect on Adelta-fibres, nor was their activity modulated by BCTC. TNBS colitis caused an immunocytochemical up-regulation of TRPV1 receptors in the cell bodies of pelvic afferent NF200 negative neurons. TRPV1 signalling mediates the colitis-induced sensitization of pelvic afferent C-fibres to CRD, while Adelta-fibres are neither sensitized by colitis nor affected by TRPV1 inhibition.

Role of transient receptor potential vanilloid‐1 (TRPV1) and cannabinoid CB1 receptors in paracetamol induced antinociception and hypothermia in mice

Paracetamol is one of the most popular and widely used analgesic antipyretics; however, its mode of action has not been clear. It was recently shown that paracetamol is metabolized in the brain and the spinal cord to form the potent TRPV1 agonist N‐acylphenolamine (AM‐404). AM‐404 is also an inhibitor of the cellular uptake of the endogenous cannabinoid, anandamide. This study was designed to study the contribution of TRPV1 and CB1 receptors in the antinociceptive and hypothermic effects of paracetamol in mice. Capsazepine, a TRPV1 antagonist, significantly reversed the antinociceptive effect of paracetamol in the formalin test, when administered i.p. at a dose of 10 mg/kg. A higher dose (30 mg/kg), however, failed to reverse the paracetamol induced antinociceptive effect. In contrast, the higher dose partially blocked paracetamol induced hypothermia but not the lower dose. Furthermore, AM‐251, a cannabinoid CB1 receptor antagonist, when administered i.p. at a dose of 10 mg/kg, reversed the antinociceptive effect of paracetamol in the formalin test and blocked paracetamol induced hypothermia after 2 hours of paracetamol injection. In conclusion, both TRPV1 and CB1 receptors are involved in paracetamol induced antinociception in mice. Hypothermia, however, might involve other mediators and further studies are needed to investigate this point.

TRP channel‐mediated calcium entry in blood‐brain barrier endothelial cells

The blood-brain barrier (BBB) is a critical regulator of brain ion homeostasis, and is disrupted in cardiovascular diseases such as stroke. In this study we examined the role of transient receptor potential (TRP) cationic channels in mediating calcium entry and barrier disruption in bEnd3 cells. We used RT-PCR, immunoblotting, fura-2 calcium imaging and functional permeability studies to investigate the involvement of TRPV and TRPC channels in mediating BBB function. Members of the TRPV family, including the flow-sensitive TRPV4, were expressed in BBB endothelial cells. These cells responded to TRPV-specific stimulation, including exposure to phorbol esters and hypo-osmotic stress, with an increase in intracellular calcium that was blocked by ruthenium red, a TRPV family antagonist. Furthermore, in a model of hypoxic stress, ruthenium red prevented hypoxia-induced increase in BBB endothelial cell monolayer permeability. These results suggest a role for TRPV channels, particularly TRPV4, in mediating BBB disruption after stroke. Ongoing studies are investigating the role of flow and TRPV channels in mediating BBB function. (NIH Grant DK070950)

TRP channels: An overview

The TRP (“transient receptor potential”) family of ion channels now comprises more than 30 cation channels, most of which are permeable for Ca 2+, and some also for Mg 2+. On the basis of sequence homology, the TRP family can be divided in seven main subfamilies: the TRPC (‘Canonical’) family, the TRPV (‘Vanilloid’) family, the TRPM (‘Melastatin’) family, the TRPP (‘Polycystin’) family, the TRPML (‘Mucolipin’) family, the TRPA (‘Ankyrin’) family, and the TRPN (‘NOMPC’) family. The cloning and characterization of members of this cation channel family has exploded during recent years, leading to a plethora of data on the roles of TRPs in a variety of tissues and species, including mammals, insects, and yeast. The present review summarizes the most pertinent recent evidence regarding the structural and functional properties of TRP channels, focusing on the regulation and physiology of mammalian TRPs.

Neurobiology of TRPC2: from gene to behavior

The mammalian vomeronasal organ (VNO), a part of the accessory olfactory system, plays an essential role in the sensing of pheromonal signals. The VNO has emerged as an excellent model to investigate the functional role of transient receptor potential (TRP) channels in intact neurons and intact physiological systems. TRPC2, a member of the (canonical) TRPC subfamily, is highly localized to the dendritic tip of vomeronasal sensory neurons. Phenotypic analysis of mice exhibiting a targeted deletion in the TRPC2 gene has established that TRPC2 occupies a fundamental role in the transduction machinery underlying the detection of pheromone signals by the VNO. TRPC2-deficient mice exhibit striking behavioral defects in the regulation of sexual and social behaviors. A previously unknown Ca(2+)-permeable, diacylglycerol (DAG)-activated cation channel found at the dendritic tip of vomeronasal neurons is severely defective in TRPC2 mutants, providing the first clear example for the existence of native DAG-gated cation channels in the mammalian nervous system. The experimental strategy employed in the mouse VNO now serves as a powerful model for examining the native functions of other TRP genes.

Regulation of epididymal principal cell functions by basal cells: role of transient receptor potential (Trp) proteins and cyclooxygenase-1 (COX-1)

The epithelia lining the epididymides of many species including the human are known to consist of several cell types. Among them, the principal cells are the most abundant and their functions most extensively studied. There are other cell types such as the narrow cells, clear cells, halo cells and basal cells which are scattered along the duct in lesser number. Although these minority cell types have not been studied to the same extent as the principal cells, it is conceivable that their presence are essential to the integrated functions of the epididymis. In the intact epididymis, basal cells can be seen adhering to the basement membrane forming close contact with the principal cells above them. Work in our laboratory has provided evidence that through local formation of prostaglandins, basal cells may regulate electrolyte and water transport by the principal cells. This regulatory process involves two proteins which are exclusively expressed by the basal cells. They are the transient receptor potential (Trp) proteins, which serve as transmembrane pathways for Ca 2+ influx, and cyclooxygenase 1 (COX-1), a key enzyme in the formation of prostaglandins. The role of the two proteins in the integrated functions of the basal cells as humoral regulators of principal cells is discussed.

"TRPping" the Switch for Store-Operated Calcium Entry

Agents that signal by increasing the intracellular concentration of free Ca 2+ often cause both release of Ca 2+ from intracellular stores and influx of Ca 2+ through channels in the plasma membrane. In fact, the emptying of intracellular stores is somehow coupled to the activation of Ca 2+ influx. Boulay et al. now help unravel two outstanding mysteries about this process—how store depletion is sensed and transmitted to the channel, and the nature of the membrane channels that actually mediate the Ca 2+ influx. Their results show that TRP channels (named after Drosophila transient receptor potential mutants) directly interact with inositol 1,4,5-trisphosphate receptors (IP3R). Expression in cells of peptide fragments from the regions of the IP3 receptor that interact with TRP caused decreased Ca 2+ entry in response to store depletion. The authors discuss, as does Putney in commentary on the paper, that the results implicate TRP channels as a component of the store depletion–activated Ca 2+ entry system. One possibility is that the IP3R may undergo a comformational change in response to the decreased concentration of Ca 2+ in the stores and physically transmit a signal to interacting TRP channels. Boulay, G., Brown, D.M., Qin, N., Jiang, M., Dietrich, A., Zhu, M.X., Chen, Z., Birnbaumer, M., Mikoshiba, K., and Birnbaumer, L. (1999) Modulation of Ca 2+ entry by polypeptides of the inositol 1,4,5-trisphosphate receptor (IP3R) that bind transient receptor potential (TRP): Evidence for roles of TRP and IP3R in store depletion-activated Ca 2+ entry. Proc. Natl. Acad. Sci. U.S.A. 96 :14955-14960. [Abstract] [Full Text] Putney, J., (1999) TRP, inositol 1,4,5-trisphosphate receptors, and capacitative calcium entry. Proc. Natl. Acad. Sci. U.S.A. 96 : 14669-14671. [Abstract] [Full Text]

Mouse trp2, the homologue of the human trpc2 pseudogene, encodes mTrp2, a store depletion-activated capacitative Ca2+ entry channel.

Capacitative Ca2+ entry (CCE) is Ca2+ entering after stimulation of inositol 1,4,5-trisphosphate (IP3) formation and initiation of Ca2+ store depletion. One hallmark of CCE is that it can also be triggered merely by store depletion, as occurs after inhibition of internal Ca2+ pumps with thapsigargin. Evidence has accumulated in support of a role of transient receptor potential (Trp) proteins as structural subunits of a class of Ca2+-permeable cation channels activated by agonists that stimulate IP3 formation-very likely through a direct interaction between the IP3 receptor and a Trp subunit of the Ca2+ entry channel. The role of Trp's in Ca2+ entry triggered by store depletion alone is less clear. Only a few of the cloned Trp's appear to enhance this type of Ca2+ entry, and when they do, the effect requires special conditions to be observed, which native CCE does not. Here we report the full-length cDNA of mouse trp2, the homologue of the human trp2 pseudogene. Mouse Trp2 is shown to be readily activated not only after stimulation with an agonist but also by store depletion in the absence of an agonist. In contrast to other Trp proteins, Trp2-mediated Ca2+ entry activated by store depletion is seen under the same conditions that reveal endogenous store depletion-activated Ca2+ entry, i.e., classical CCE. The findings support the general hypothesis that Trp proteins are subunits of store- and receptor-operated Ca2+ channels.