Functional expression of transient receptor potential vanilloid-related channels in chronically hypoxic human pulmonary arterial smooth muscle cells

Cultured rat aortic vascular smooth muscle cells do not express a functional TRPV1

We showed previously that capsaicin, an active compound of chili peppers, can inhibit platelet-derived growth factor-induced proliferation in primary rat vascular smooth muscle cells (VSMCs). The inhibition of BrdU incorporation by capsaicin in these cells was revoked by BCTC, which might be explained by a role of TRPV1 in VSMCs proliferation. To further pursue the hypothesis of a TRPV1-dependent effect of capsaicin, we investigated TRPV1 expression and function. Commercially available antibodies against two different TRPV1 epitopes (N-terminus and C-terminus) were rendered invalid in detecting TRPV1, as shown: i) in western blot experiments using control lysates of TRPV1-expressing (PC-12 and hTRPV1 transfected HEK293T) and TRPV1-downregulated (CRISPR/Cas gene edited A10) cells, and ii) by substantial differences in staining patterns between the applied antibodies using fluorescence confocal microscopy. The TRPV1 agonists capsaicin, resiniferatoxin, piperine and evodiamine did not increase intracellular calcium levels in primary VSMCs and in A10 cells. Using RT qPCR, we could detect a rather low TRPV1 expression in VSMCs at the mRNA level (Cp value around 30), after validating the primer pair in NGF-stimulated PC-12 cells. We conclude that rat vascular smooth muscle cells do not possess canonical TRPV1 channel activity, which could explain the observed antiproliferative effect of capsaicin.

FUNDC1-mediated mitophagy and HIF1α activation drives pulmonary hypertension during hypoxia

Hypoxic pulmonary hypertension (PH) is a progressive disease characterized by hyper-proliferation of pulmonary vascular cells including pulmonary artery smooth muscle cells (PASMCs) and can lead to right heart failure and early death. Selective degradation of mitochondria by mitophagy during hypoxia regulates mitochondrial functions in many cells, however, it is not clear if mitophagy is involved in the pathogenesis of hypoxic PH. By employing the hypoxic mitophagy receptor Fundc1 knockout (KO) and transgenic (TG) mouse models, combined hypoxic PH models, the current study found that mitophagy is actively involved in hypoxic PH through regulating PASMC proliferation. In the pulmonary artery medium from hypoxic PH mice, mitophagy was upregulated, accompanied with the increased active form of FUNDC1 protein and the enhanced binding affinity of FUNDC1 with LC3B. In PASMCs, overexpression of FUNDC1 increased mitophagy and cell proliferation while knockdown of FUNDC1 inhibited hypoxia-induced mitophagy and PASMC proliferation. Stimulation of mitophagy by FUNDC1 in PASMCs elevated ROS production and inhibited ubiquitination of hypoxia inducible factor 1α (HIF1α), and inhibition of mitophagy by FUNDC1 knockdown or knockout abolished hypoxia-induced ROS-HIF1α upregulation. Moreover, Fundc1 TG mice developed severe hemodynamics changes and pulmonary vascular remodeling, and Fundc1 KO mice were much resistant to hypoxic PH. In addition, intraperitoneal injection of a specific FUNDC1 peptide inhibitor to block mitophagy ameliorated hypoxic PH. Our results reveal that during hypoxic PH, FUNDC1-mediated mitophagy is upregulated which activates ROS-HIF1α pathway and promotes PASMC proliferation, ultimately leads to pulmonary vascular remodeling and PH.

Ca2+ Signalling and Hypoxia/Acidic Tumour Microenvironment Interplay in Tumour Progression

Solid tumours are characterised by an altered microenvironment (TME) from the physicochemical point of view, displaying a highly hypoxic and acidic interstitial fluid. Hypoxia results from uncontrolled proliferation, aberrant vascularization and altered cancer cell metabolism. Tumour cellular apparatus adapts to hypoxia by altering its metabolism and behaviour, increasing its migratory and metastatic abilities by the acquisition of a mesenchymal phenotype and selection of aggressive tumour cell clones. Extracellular acidosis is considered a cancer hallmark, acting as a driver of cancer aggressiveness by promoting tumour metastasis and chemoresistance via the selection of more aggressive cell phenotypes, although the underlying mechanism is still not clear. In this context, Ca2+ channels represent good target candidates due to their ability to integrate signals from the TME. Ca2+ channels are pH and hypoxia sensors and alterations in Ca2+ homeostasis in cancer progression and vascularization have been extensively reported. In the present review, we present an up-to-date and critical view on Ca2+ permeable ion channels, with a major focus on TRPs, SOCs and PIEZO channels, which are modulated by tumour hypoxia and acidosis, as well as the consequent role of the altered Ca2+ signals on cancer progression hallmarks. We believe that a deeper comprehension of the Ca2+ signalling and acidic pH/hypoxia interplay will break new ground for the discovery of alternative and attractive therapeutic targets.

Capsaicin and TRPV1 Channels in the Cardiovascular System: The Role of Inflammation

Capsaicin is a potent agonist of the Transient Receptor Potential Vanilloid type 1 (TRPV1) channel and is a common component found in the fruits of the genus Capsicum plants, which have been known to humanity and consumed in food for approximately 7000-9000 years. The fruits of Capsicum plants, such as chili pepper, have been long recognized for their high nutritional value. Additionally, capsaicin itself has been proposed to exhibit vasodilatory, antimicrobial, anti-cancer, and antinociceptive properties. However, a growing body of evidence reveals a vasoconstrictory potential of capsaicin acting via the vascular TRPV1 channel and suggests that unnecessary high consumption of capsaicin may cause severe consequences, including vasospasm and myocardial infarction in people with underlying inflammatory conditions. This review focuses on vascular TRPV1 channels that are endogenously expressed in both vascular smooth muscle and endothelial cells and emphasizes the role of inflammation in sensitizing the TRPV1 channel to capsaicin activation. Tilting the balance between the beneficial vasodilatory action of capsaicin and its unwanted vasoconstrictive effects may precipitate adverse outcomes such as vasospasm and myocardial infarction, especially in the presence of proinflammatory mediators.

Mechanosensitivity in Pulmonary Circulation: Pathophysiological Relevance of Stretch-Activated Channels in Pulmonary Hypertension

A variety of cell types in pulmonary arteries (endothelial cells, fibroblasts, and smooth muscle cells) are continuously exposed to mechanical stimulations such as shear stress and pulsatile blood pressure, which are altered under conditions of pulmonary hypertension (PH). Most functions of such vascular cells (e.g., contraction, migration, proliferation, production of extracellular matrix proteins, etc.) depend on a key event, i.e., the increase in intracellular calcium concentration ([Ca²⁺]_i) which results from an influx of extracellular Ca²⁺ and/or a release of intracellular stored Ca²⁺. Calcium entry from the extracellular space is a major step in the elevation of [Ca²⁺]_i, involving a variety of plasmalemmal Ca²⁺ channels including the superfamily of stretch-activated channels (SAC). A common characteristic of SAC is that their gating depends on membrane stretch. In general, SAC are non-selective Ca²⁺-permeable cation channels, including proteins of the TRP (Transient Receptor Potential) and Piezo channel superfamily. As membrane mechano-transducers, SAC convert physical forces into biological signals and hence into a cell response. Consequently, SAC play a major role in pulmonary arterial calcium homeostasis and, thus, appear as potential novel drug targets for a better management of PH.

The expanded effects of sevoflurane on the nervous system: the harmful effect of residual concentration of sevoflurane on the respiratory system through neurogenic inflammation

Background

Neurogenic inflammation caused by sevoflurane may not only limite to the nervous system, but also expand to the respiratory system. The purpose of this study was to investigate the expression changes of transient receptor potential vanilloid 1 (TRPV1), neurokinin A (NKA), neurokinin B (NKB), calcitonin gene related peptide (CGRP) and substance P (SP) in 14, 21 and 42-day-old rats after inhaling 0.4% sevoflurane, in order to evaluate whether the residual sevoflurane be harmful to the respiratory system through neurogenic inflammation.

Methods

The anesthetic inhalation device was designed to allow 14, 21 and 42-day-old rats inhale 0.4% sevoflurane, while rats in the control group inhaled 40% O2 for 1h. Rats in the antagonist group inhaled 0.4% sevoflurane or 40% O2 for 1 h after Capsazepine (CPZ) pretreatment. The expression of TRPV1 in lung tissue was detected by western blot, and the expression of NKA, NKB, CGRP and SP in trachea was detected by immunohistochemistry.

Results

After inhaling 0.4% sevoflurane, the expression of TRPV1 in lung tissue of 14 and 21-day-old rats was significantly higher than that of the control group, as well as increased the expression of CGRP and SP in the trachea of 14-day-old rats and NKA, NKB, CGRP and SP in the trachea of 21-day-old rats. CPZ pretreatment could antagonize these effects.

Conclusion

Residual sevoflurane during resuscitation of inhalation anesthesia could induce neurogenic inflammation by activating TRPV1, which damaged to the developing respiratory system, but has no significant effect on the respiratory system in adulthood.

The potential role of TRPV1 in pulmonary hypertension: Angel or demon?

Pulmonary hypertension (PH) is a pathological state defined by increased pulmonary artery pressure, the pathogenesis of which is related to genetic mutations, intracellular calcium ([Ca²⁺]_i), inflammation and proliferation. Transient receptor potential vanilloid subfamily member 1 (TRPV1) is a nonselective cation channel expressed in neural and nonneural cells, including pulmonary vessels and nerves. As a calcium channel, TRPV1 can make vessels contracted, and promote smooth muscle cells proliferation through calcium-dependent transcription factors. Activation of TRPV1 in sensory nerves can release neuropeptides, including calcitonin gene-related peptide (CGRP), substance P (SP), and somatostatin (SST), which can regulate inflammation via transcription factor NF-kB. Considering the increased level of [Ca²⁺]_i and inflammation in the pathogenesis of PH, our review summarizes the role of TRPV1 in PH with regard to [Ca²⁺]_i, neuropeptides, and inflammation. In view of the limited research illustrating the relationship between TRPV1 and PH directly, our review also considers the role of TRPV1 in other types of vascular inflammation. Through this review, we hope to raise awareness about the function of TRPV1 in PH.

"TRPV1 is a component of the atrial natriuretic signaling complex, and using orally delivered antagonists, presents a valid therapeutic target in the longitudinal reversal and treatment of cardiac hypertrophy and heart failure"

Activation of the atrial natriuretic signaling pathway is intrinsic to the pathological responses associated with a range of cardiovascular diseases that stress the heart, especially those involved in sustained cardiac pressure overload which induces hypertrophy and the pathological remodeling that frequently leads to heart failure. We identify transient receptor potential cation channel, subfamily V, member 1, as a regulated molecular component, and therapeutic target of this signaling system. Data show that TRPV1 is a physical component of the natriuretic peptide A, cGMP, PKG signaling complex, interacting with the Natriuretic Peptide Receptor 1 (NPR1), and upon binding its ligand, Natriuretic Peptide A (NPPA, ANP) TRPV1 activation is subsequently suppressed through production of cGMP and PKG mediated phosphorylation of the TRPV1 channel. Further, inhibition of TRPV1, with orally delivered drugs, suppresses chamber and myocyte hypertrophy, and can longitudinally improve in vivo heart function in mice exposed to chronic pressure overload induced by transverse aortic constriction, reversing pre-established hypertrophy induced by pressure load while restoring chamber function. TRPV1 is a physical and regulated component of the natriuretic peptide signaling system, and TRPV1 inhibition may provide a new treatment strategy for treating, and reversing the loss of function associated with cardiac hypertrophy and heart failure.

Modulators of Transient Receptor Potential (TRP) Channels as Therapeutic Options in Lung Disease

The lungs are essential for gas exchange and serve as the gateways of our body to the external environment. They are easily accessible for drugs from both sides, the airways and the vasculature. Recent literature provides evidence for a role of Transient Receptor Potential (TRP) channels as chemosensors and essential members of signal transduction cascades in stress-induced cellular responses. This review will focus on TRP channels (TRPA1, TRPC6, TRPV1, and TRPV4), predominantly expressed in non-neuronal lung tissues and their involvement in pathways associated with diseases like asthma, cystic fibrosis, chronic obstructive pulmonary disease (COPD), lung fibrosis, and edema formation. Recently identified specific modulators of these channels and their potential as new therapeutic options as well as strategies for a causal treatment based on the mechanistic understanding of molecular events will also be evaluated.

Extra-endothelial TRPV1 channels participate in alcohol and caffeine actions on cerebral artery diameter

Alcohol (ethyl alcohol; ethanol) and caffeine are the two most widely used psychoactive substances in the world. Caffeine and ethanol have both been reported to constrict cerebral arteries in several species, including humans. We have recently shown that application of 10-μM caffeine mixed with 50 mM ethanol to in vitro pressurized cerebral arteries of rats reduced ethanol-induced constriction. This effect was dependent on the presence of nitric oxide (NO^•) and could be observed in de-endothelialized arteries supplied with the NO donor sodium nitroprusside (SNP). The molecular target(s) of ethanol-caffeine interaction in cerebral arteries has remained unknown. In the present work, we used rat and mouse middle cerebral arteries (MCA) to identify the extra-endothelial effectors of NO-mediated, caffeine-induced protection against ethanol-evoked arterial constriction. Constriction of intact MCA of rat by either 50 mM ethanol or 10 μM caffeine was ablated in the presence of a selective TRPV1 pharmacological blocker. TRPV1 pharmacological block, but not block of TRPA1, PKG, or BK channels, removed caffeine-induced protection against ethanol-evoked rat MCA constriction, whether evaluated in arteries with intact endothelium or in SNP-supplemented, de-endothelialized arteries. In mouse arteries, caffeine-induced protection against ethanol-induced MCA constriction was significantly amplified, resulting in actual vasodilation, upon pharmacological block of TRPV1, and in TRPV1 knock-out arteries. Despite some species-specific differences, our study unequivocally demonstrates the presence of functional, extra-endothelial TRPV1 that participates in both endothelium-independent MCA constriction by separate exposure to ethanol or caffeine and caffeine-induced protection against ethanol-evoked MCA constriction.

The Regulation of Pulmonary Vascular Tone by Neuropeptides and the Implications for Pulmonary Hypertension

Pulmonary hypertension (PH) is an incurable, chronic disease of small pulmonary vessels. Progressive remodeling of the pulmonary vasculature results in increased pulmonary vascular resistance (PVR). This causes secondary right heart failure. PVR is tightly regulated by a range of pulmonary vasodilators and constrictors. Endothelium-derived substances form the basis of most current PH treatments. This is particularly the case for pulmonary arterial hypertension. The major limitation of current treatments is their inability to reverse morphological changes. Thus, there is an unmet need for novel therapies to reduce the morbidity and mortality in PH. Microvessels in the lungs are highly innervated by sensory C fibers. Substance P and calcitonin gene-related peptide (CGRP) are released from C-fiber nerve endings. These neuropeptides can directly regulate vascular tone. Substance P tends to act as a vasoconstrictor in the pulmonary circulation and it increases in the lungs during experimental PH. The receptor for substance P, neurokinin 1 (NK1R), mediates increased pulmonary pressure. Deactivation of NK1R with antagonists, or depletion of substance P prevents PH development. CGRP is a potent pulmonary vasodilator. CGRP receptor antagonists cause elevated pulmonary pressure. Thus, the balance of these peptides is crucial within the pulmonary circulation (Graphical Abstract). Limited progress has been made in understanding their impact on pulmonary pathophysiology. This is an intriguing area of investigation to pursue. It may lead to promising new candidate therapies to combat this fatal disease. This review provides a summary of the current knowledge in this area. It also explores possible future directions for neuropeptides in PH.

Capsaicin-induced Ca2+ signaling is enhanced via upregulated TRPV1 channels in pulmonary artery smooth muscle cells from patients with idiopathic PAH

Capsaicin is an active component of chili pepper and a pain relief drug. Capsaicin can activate transient receptor potential vanilloid 1 (TRPV1) channels to increase cytosolic Ca²⁺ concentration ([Ca²⁺]_cyt). A rise in [Ca²⁺]_cyt in pulmonary artery smooth muscle cells (PASMCs) is an important stimulus for pulmonary vasoconstriction and vascular remodeling. In this study, we observed that a capsaicin-induced increase in [Ca²⁺]_cyt was significantly enhanced in PASMCs from patients with idiopathic pulmonary arterial hypertension (IPAH) compared with normal PASMCs from healthy donors. In addition, the protein expression level of TRPV1 in IPAH PASMCs was greater than in normal PASMCs. Increasing the temperature from 23 to 43°C, or decreasing the extracellular pH value from 7.4 to 5.9 enhanced capsaicin-induced increases in [Ca²⁺]_cyt; the acidity (pH 5.9)- and heat (43°C)-mediated enhancement of capsaicin-induced [Ca²⁺]_cyt increases were greater in IPAH PASMCs than in normal PASMCs. Decreasing the extracellular osmotic pressure from 310 to 200 mOsmol/l also increased [Ca²⁺]_cyt, and the hypo-osmolarity-induced rise in [Ca²⁺]_cyt was greater in IPAH PASMCs than in healthy PASMCs. Inhibition of TRPV1 (with 5'-IRTX or capsazepine) or knockdown of TRPV1 (with short hairpin RNA) attenuated capsaicin-, acidity-, and osmotic stretch-mediated [Ca²⁺]_cyt increases in IPAH PASMCs. Capsaicin induced phosphorylation of CREB by raising [Ca²⁺]_cyt, and capsaicin-induced CREB phosphorylation were significantly enhanced in IPAH PASMCs compared with normal PASMCs. Pharmacological inhibition and knockdown of TRPV1 attenuated IPAH PASMC proliferation. Taken together, the capsaicin-mediated [Ca²⁺]_cyt increase due to upregulated TRPV1 may be a critical pathogenic mechanism that contributes to augmented Ca²⁺ influx and excessive PASMC proliferation in patients with IPAH.

Mitogen-Activated Protein Kinase and Intracellular Polyamine Signaling Is Involved in TRPV1 Activation-Induced Cardiac Hypertrophy

BACKGROUND

The transient receptor potential vanilloid type 1 (TRPV1) is expressed in the cardiovascular system, and increased TRPV1 expression has been associated with cardiac hypertrophy. Nevertheless, the role of TRPV1 in the pathogenesis of cardiac hypertrophy and the underlying molecular mechanisms remain unclear.

METHODS AND RESULTS

In cultured cardiomyocytes, activation of TRPV1 increased cell size and elevated expression of atrial natriuretic peptide mRNA and intracellular calcium level, which was reversed by TRPV1 antagonist capsazepine. Increased expression of phosphorylated calmodulin-dependent protein kinase IIδ and mitogen-activated protein kinases were found in TRPV1 agonist capsaicin-treated cardiomyocytes. Selective inhibitor of calmodulin-dependent protein kinase IIδ decreased phosphorylation of extracellular signal-regulated kinases and p38. Capsaicin induced an increase in expression of ornithine decarboxylase protein, which is the key enzyme in polyamine biosynthesis in cardiomyocytes. Nevertheless, there was no obvious change of ornithine decarboxylase expression in TRPV1 knockdown cells after capsaicin treatment, and specific inhibitors of calmodulin-dependent protein kinase IIδ or p38 downregulated the capsaicin-induced expression of ornithine decarboxylase. Capsazepine alleviated the increase in cross-sectional area of cardiomyocytes and the ratio of heart weight to body weight and improved cardiac function, including left ventricular internal end-diastolic and -systolic dimensions and ejection fraction and fractional shortening percentages, in mice treated with transverse aorta constriction. Capsazepine also reduced expression of ornithine decarboxylase and cardiac polyamine levels. Transverse aorta constriction induced increases in phosphorylated calmodulin-dependent protein kinase IIδ and extracellular signal-regulated kinases, and p38 and Serca2a were attenuated by capsazepine treatment.

CONCLUSIONS

This study revealed that the mitogen-activated protein kinase signaling pathway and intracellular polyamines are essential for TRPV1 activation-induced cardiac hypertrophy.

TRPV-1-mediated elimination of residual iPS cells in bioengineered cardiac cell sheet tissues

The development of a suitable strategy for eliminating remaining undifferentiated cells is indispensable for the use of human-induced pluripotent stem (iPS) cell-derived cells in regenerative medicine. Here, we show for the first time that TRPV-1 activation through transient culture at 42 °C in combination with agonists is a simple and useful strategy to eliminate iPS cells from bioengineered cardiac cell sheet tissues. When human iPS cells were cultured at 42 °C, almost all cells disappeared by 48 hours through apoptosis. However, iPS cell-derived cardiomyocytes and fibroblasts maintained transcriptional and protein expression levels, and cardiac cell sheets were fabricated after reducing the temperature. TRPV-1 expression in iPS cells was upregulated at 42 °C, and iPS cell death at 42 °C was TRPV-1-dependent. Furthermore, TRPV-1 activation through thermal or agonist treatment eliminated iPS cells in cardiac tissues for a final concentration of 0.4% iPS cell contamination. These findings suggest that the difference in tolerance to TRPV-1 activation between iPS cells and iPS cell-derived cardiac cells could be exploited to eliminate remaining iPS cells in bioengineered cell sheet tissues, which will further reduce the risk of tumour formation.

TPRV-1 expression in human preeclamptic placenta

Preeclampsia is a multisystem disorder unique to human pregnancy, characterized by abnormal placentation. Although its causes remain unclear, it is known that the expression of several transporters is altered. Transient receptor potential vanilloid 1 (TRPV-1) is a nonselective cation channel, present in human placenta. Here, we evaluated the expression of TRPV-1 in preeclamptic placentas. We observed a deregulation in TRPV-1 expression in these placentas which may explain the impaired Ca(2+) homeostasis found in preeclampsia.

Transient receptor potential channels in the vasculature

The mammalian genome encodes 28 distinct members of the transient receptor potential (TRP) superfamily of cation channels, which exhibit varying degrees of selectivity for different ionic species. Multiple TRP channels are present in all cells and are involved in diverse aspects of cellular function, including sensory perception and signal transduction. Notably, TRP channels are involved in regulating vascular function and pathophysiology, the focus of this review. TRP channels in vascular smooth muscle cells participate in regulating contractility and proliferation, whereas endothelial TRP channel activity is an important contributor to endothelium-dependent vasodilation, vascular wall permeability, and angiogenesis. TRP channels are also present in perivascular sensory neurons and astrocytic endfeet proximal to cerebral arterioles, where they participate in the regulation of vascular tone. Almost all of these functions are mediated by changes in global intracellular Ca(2+) levels or subcellular Ca(2+) signaling events. In addition to directly mediating Ca(2+) entry, TRP channels influence intracellular Ca(2+) dynamics through membrane depolarization associated with the influx of cations or through receptor- or store-operated mechanisms. Dysregulation of TRP channels is associated with vascular-related pathologies, including hypertension, neointimal injury, ischemia-reperfusion injury, pulmonary edema, and neurogenic inflammation. In this review, we briefly consider general aspects of TRP channel biology and provide an in-depth discussion of the functions of TRP channels in vascular smooth muscle cells, endothelial cells, and perivascular cells under normal and pathophysiological conditions.

Effect of hypoxia on TRPV1 and TRPV4 channels in rat pulmonary arterial smooth muscle cells

Transient receptor potential (TRP) channels of the vanilloid subfamily, mainly TRPV1 and TRPV4, are expressed in pulmonary artery smooth muscle cells (PASMC) and implicated in the remodeling of pulmonary artery, a landmark of pulmonary hypertension (PH). Among a variety of PH subtypes, PH of group 3 are mostly related to a prolonged hypoxia exposure occurring in a variety of chronic lung diseases. In the present study, we thus investigated the role of hypoxia on TRPV1 and TRPV4 channels independently of the increased pulmonary arterial pressure that occurs during PH. We isolated PASMC from normoxic rat and cultured these cells under in vitro hypoxia. Using microspectrofluorimetry and the patch-clamp technique, we showed that hypoxia (1 % O2 for 48 h) significantly increased stretch- and TRPV4-induced calcium responses. qRT-PCR, Western blotting, and immunostaining experiments revealed that the expression of TRPV1 and TRPV4 was not enhanced under hypoxic conditions, but we observed a membrane translocation of TRPV1. Furthermore, hypoxia induced a reorganization of the F-actin cytoskeleton, the tubulin, and intermediate filament networks (immunostaining experiments), associated with an enhanced TRPV1- and TRPV4-induced migratory response (wound-healing assay). Finally, as assessed by immunostaining, exposure to in vitro hypoxia elicited a significant increase in NFATc4 nuclear localization. Cyclosporin A and BAPTA-AM inhibited NFATc4 translocation, indicating the activation of the Ca(2+)/calcineurin/NFAT pathway. In conclusion, these data point out the effect of hypoxia on TRPV1 and TRPV4 channels in rat PASMC, suggesting that these channels can act as direct signal transducers in the pathophysiology of PH.

Role of TRP channels in the cardiovascular system

The transient receptor potential (TRP) superfamily consists of a large number of nonselective cation channels with variable degree of Ca(2+)-permeability. The 28 mammalian TRP channel proteins can be grouped into six subfamilies: canonical, vanilloid, melastatin, ankyrin, polycystic, and mucolipin TRPs. The majority of these TRP channels are expressed in different cell types including both excitable and nonexcitable cells of the cardiovascular system. Unlike voltage-gated ion channels, TRP channels do not have a typical voltage sensor, but instead can sense a variety of other stimuli including pressure, shear stress, mechanical stretch, oxidative stress, lipid environment alterations, hypertrophic signals, and inflammation products. By integrating multiple stimuli and transducing their activity to downstream cellular signal pathways via Ca(2+) entry and/or membrane depolarization, TRP channels play an essential role in regulating fundamental cell functions such as contraction, relaxation, proliferation, differentiation, and cell death. With the use of targeted deletion and transgenic mouse models, recent studies have revealed that TRP channels are involved in numerous cellular functions and play an important role in the pathophysiology of many diseases in the cardiovascular system. Moreover, several TRP channels are involved in inherited diseases of the cardiovascular system. This review presents an overview of current knowledge concerning the physiological functions of TRP channels in the cardiovascular system and their contributions to cardiovascular diseases. Ultimately, TRP channels may become potential therapeutic targets for cardiovascular diseases.

α1- and α2-adrenergic responsiveness in human skeletal muscle feed arteries: the role of TRPV ion channels in heat-induced sympatholysis

The purpose of this study was to determine if heat inhibits α2-adrenergic vasocontraction, similarly to α1-adrenergic contraction, in isolated human skeletal muscle feed arteries (SMFA) and elucidate the role of the temperature-sensitive vanilloid-type transient receptor potential (TRPV) ion channels in this response. Isolated SMFA from 37 subjects were studied using wire myography. α1 [Phenylephrine (PE)]- and α2 [dexmedetomidine (DEX)]-contractions were induced at 37 and 39°C with and without TRPV family and TRPV4-specific inhibition [ruthenium red (RR) and RN-1734, respectively]. Endothelial function [acetylcholine (ACh)] and smooth muscle function [sodium nitroprusside (SNP) and potassium chloride (KCl)] were also assessed under these conditions. Heat and TRPV inhibition was further examined in endothelium-denuded arteries. Contraction data are reported as a percentage of maximal contraction elicited by 100 mM KCl (LTmax). DEX elicited a small and variable contractile response, one-fifth the magnitude of PE, which was not as clearly attenuated when heated from 37 to 39°C (12 ± 4 to 6 ± 2% LTmax; P = 0.18) as were PE-induced contractions (59 ± 5 to 24 ± 4% LTmax; P < 0.05). Both forms of TRPV inhibition restored PE-induced contraction at 39°C (P < 0.05) implicating these channels, particularly the TRPV4 channels, in the heat-induced attenuation of α1-adrenergic vasocontraction. TRPV inhibition significantly blunted ACh relaxation while denudation prevented heat-induced sympatholysis without having an additive effect when combined with TRPV inhibition. In conclusion, physiological increases in temperature elicit a sympatholysis-like inhibition of α1-adrenergic vasocontraction in human SMFA that appears to be mediated by endothelial TRPV4 ion channels.

The role of ion channels in the hypoxia-induced aggressiveness of glioblastoma

The malignancy of glioblastoma multiform (GBM), the most common and aggressive form of human brain tumors, strongly correlates with the presence of hypoxic areas, but the mechanisms controlling the hypoxia-induced aggressiveness are still unclear. GBM cells express a number of ion channels whose activity supports cell volume changes and increases in the cytosolic Ca²⁺ concentration, ultimately leading to cell proliferation, migration or death. In several cell types it has previously been shown that low oxygen levels regulate the expression and activity of these channels, and more recent data indicate that this also occurs in GBM cells. Based on these findings, it may be hypothesized that the modulation of ion channel activity or expression by the hypoxic environment may participate in the acquisition of the aggressive phenotype observed in GBM cells residing in a hypoxic environment. If this hypothesis will be confirmed, the use of available ion channels modulators may be considered for implementing novel therapeutic strategies against these tumors.

Vascular targets for cannabinoids: animal and human studies

Application of cannabinoids and endocannabinoids to perfused vascular beds or individual isolated arteries results in changes in vascular resistance. In most cases, the result is vasorelaxation, although vasoconstrictor responses are also observed. Cannabinoids also modulate the actions of vasoactive compounds including acetylcholine, methoxamine, angiotensin II and U46619 (thromboxane mimetic). Numerous mechanisms of action have been proposed including receptor activation, potassium channel activation, calcium channel inhibition and the production of vasoactive mediators such as calcitonin gene-related peptide, prostanoids, NO, endothelial-derived hyperpolarizing factor and hydrogen peroxide. The purpose of this review is to examine the evidence for the range of receptors now known to be activated by cannabinoids. Direct activation by cannabinoids of CB1 , CBe , TRPV1 (and potentially other TRP channels) and PPARs in the vasculature has been observed. A potential role for CB2, GPR55 and 5-HT1 A has also been identified in some studies. Indirectly, activation of prostanoid receptors (TP, IP, EP1 and EP4 ) and the CGRP receptor is involved in the vascular responses to cannabinoids. The majority of this evidence has been obtained through animal research, but recent work has confirmed some of these targets in human arteries. Vascular responses to cannabinoids are enhanced in hypertension and cirrhosis, but are reduced in obesity and diabetes, both due to changes in the target sites of action. Much further work is required to establish the extent of vascular actions of cannabinoids and the application of this research in physiological and pathophysiological situations.

LINKED ARTICLES

This article is part of a themed section on Cannabinoids 2013. To view the other articles in this section visit http://dx.doi.org/10.1111/bph.2014.171.issue-6.

Effect of TRPV1 channel on proliferation and apoptosis of airway smooth muscle cells of rats

Airway remodeling is an important pathological feature of asthma and the basis of severe asthma. Proliferation of airway smooth muscle cells (ASMCs) is a major contributor to airway remodeling. As an important Ca(2+) channel, transient receptor potential vanilloid 1 (TRPV1) plays the key role in the cell pathological and physiological processes. This study investigated the expression and activity of TRPV1 channel, and further clarified the effect of TRPV1 channel on the ASMCs proliferation and apoptosis in order to provide the scientific basis to treat asthmatic airway remodeling in clinical practice. Immunofluorescence staining and reverse transcription polymerase chain reaction (RT-PCR) were used to detect the expression of TRPV1 in rat ASMCs. Intracellular Ca(2+) was detected using the single cell confocal fluorescence microscopy measurement loaded with Fluo-4/AM. The cell cycles were observed by flow cytometry. MTT assay and Hoechst 33258 staining were used to detect the proliferation and apoptosis of ASMCs in rats respectively. The data showed that: (1) TRPV1 channel was present in rat ASMCs. (2) TRPV1 channel agonist, capsaicin, increased the Ca(2+) influx in a concentration-dependent manner (EC50=284.3±58 nmol/L). TRPV1 channel antagonist, capsazepine, inhibited Ca(2+) influx in rat ASMCs. (3) Capsaicin significantly increased the percentage of S+G2M ASMCs and the absorbance of MTT assay. Capsazepine had the opposite effect. (4) Capsaicin significantly inhibited the apoptosis, whereas capsazepine had the opposite effect. These results suggest that TRPV1 is present and mediates Ca(2+) influx in rat ASMCs. TRPV1 activity stimulates proliferation of ASMCs in rats.

Anatomical and physiological factors contributing to chronic muscle pain

Chronic muscle pain remains a significant source of suffering and disability despite the adoption of pharmacologic and physical therapies. Muscle pain is mediated by free nerve endings distributed through the muscle along arteries. These nerves project to the superficial dorsal horn and are transmitted primarily through the spinothalamic tract to several cortical and subcortical structures, some of which are more active during the processing of muscle pain than other painful conditions. Mechanical forces, ischemia, and inflammation are the primary stimuli for muscle pain, which is reflected in the array of peripheral receptors contributing to muscle pain-ASIC, P2X, and TRP channels. Sensitization of peripheral receptors and of central pain processing structures are both critical for the development and maintenance of chronic muscle pain. Further, variations in peripheral receptors and central structures contribute to the significantly greater prevalence of chronic muscle pain in females.

Cyclooxygenase metabolism mediates vasorelaxation to 2-arachidonoylglycerol (2-AG) in human mesenteric arteries

Objective

The vasorelaxant effect of 2-arachidonoylglycerol (2-AG) has been well characterised in animals. 2-AG is present in human vascular cells and is up-regulated in cardiovascular pathophysiology. However, the acute vascular actions of 2-AG have not been explored in humans.

Approach

Mesenteric arteries were obtained from patients receiving colorectal surgery and mounted on a myograph. Arteries were contracted and 2-AG concentration–response curves were carried out. Mechanisms of action were characterised pharmacologically. Post hoc analysis was carried out to assess the effects of cardiovascular disease/risk factors on 2-AG responses.

Results

2-AG caused vasorelaxation of human mesenteric arteries, independent of cannabinoid receptor or transient receptor potential vanilloid-1 activation, the endothelium, nitric oxide or metabolism via monoacyglycerol lipase or fatty acid amide hydrolase. 2-AG-induced vasorelaxation was reduced in the presence of indomethacin and flurbiprofen, suggesting a role for cyclooxygenase metabolism 2-AG. Responses to 2-AG were also reduced in the presence of Cay10441, L-161982 and potentiated in the presence of AH6809, suggesting that metabolism of 2-AG produces both vasorelaxant and vasoconstrictor prostanoids. Finally, 2-AG-induced vasorelaxation was dependent on potassium efflux and the presence of extracellular calcium.

Conclusions

We have shown for the first time that 2-AG causes vasorelaxation of human mesenteric arteries. Vasorelaxation is dependent on COX metabolism, activation of prostanoid receptors (EP₄ & IP) and ion channel modulation. 2-AG responses are blunted in patients with cardiovascular risk factors.

Endothelial and smooth muscle cell ion channels in pulmonary vasoconstriction and vascular remodeling

The pulmonary circulation is a low resistance and low pressure system. Sustained pulmonary vasoconstriction and excessive vascular remodeling often occur under pathophysiological conditions such as in patients with pulmonary hypertension. Pulmonary vasoconstriction is a consequence of smooth muscle contraction. Many factors released from the endothelium contribute to regulating pulmonary vascular tone, while the extracellular matrix in the adventitia is the major determinant of vascular wall compliance. Pulmonary vascular remodeling is characterized by adventitial and medial hypertrophy due to fibroblast and smooth muscle cell proliferation, neointimal proliferation, intimal, and plexiform lesions that obliterate the lumen, muscularization of precapillary arterioles, and in situ thrombosis. A rise in cytosolic free Ca(2+) concentration ([Ca(2+)]cyt) in pulmonary artery smooth muscle cells (PASMC) is a major trigger for pulmonary vasoconstriction, while increased release of mitogenic factors, upregulation (or downregulation) of ion channels and transporters, and abnormalities in intracellular signaling cascades are key to the remodeling of the pulmonary vasculature. Changes in the expression, function, and regulation of ion channels in PASMC and pulmonary arterial endothelial cells play an important role in the regulation of vascular tone and development of vascular remodeling. This article will focus on describing the ion channels and transporters that are involved in the regulation of pulmonary vascular function and structure and illustrating the potential pathogenic role of ion channels and transporters in the development of pulmonary vascular disease.

The effect of Shenmai injection on the proliferation of Rat airway smooth muscle cells in asthma and underlying mechanism

BACKGROUND

Over-proliferation of airway smooth muscle cell (ASMC) is one of the important contributors to airway remodeling in asthma. The aim of this study was to investigate the effect of Shenmai injection (SMI) on the proliferation of the rat ASMC in asthma.

METHODS

Rats were randomly divided into three groups: the control group, the asthma group, and the SMI treatment group. Reverse transcription-polymerase chain reaction (RT-PCR) and immunocytochemistry staining were used to detect the mRNA and protein expression of transient receptor potential vanilloid 1 (TRPV1) and proliferating cell nuclear antigen (PCNA) in rat ASMC respectively. Intracellular Ca²⁺ concentration ( [Ca²⁺](i)) in rat ASMC were measured with Fluo-3/AM by confocal microscopy. The proliferation was detected by MTT assay.

RESULTS

Compared with the control group, the asthma group showed an increased expression of TRPV1 and [Ca²⁺](i) in rat ASMC. The expression of PCNA and absorbance of MTT assay in asthma rat ASMC was also significantly increased. SMI could significantly decrease the expression of TRPV1 channel and [Ca²⁺](i) in the asthmatic rat ASMC. Furthermore, the expression of PCNA and absorbance of MTT assay in asthmatic rat ASMC was significantly reduced after SMI treatment.

CONCLUSIONS

SMI may prevent asthma-induced ASMC over-proliferation probably by inhibiting the expression of TRPV1 channel, which regulates the intracellular calcium concentration.

Effect of TRPV1 channel on the proliferation and apoptosis in asthmatic rat airway smooth muscle cells

BACKGROUND

Hyperplasia of airway smooth muscle cells (ASMC) is a major contributor to airway remodeling in asthma. Transient receptor potential vanilloid 1 (TRPV1) is an important channel to mediate Ca(2+) influx. This study explores the expression of TRPV1 channel and its effect on the proliferation and apoptosis in rat ASMC, in order to find a new target to treat airway remodeling in asthma.

METHODS

Rats were sensitized and challenged with ovalbumin to replicate asthmatic models. Proliferating cell nuclear antigen (PCNA) was detected by immunohistochemistry. Reverse transcriptase-polymerase chain reaction, immunocytochemistry, and Western blot were used to detect the mRNA and protein expression of TRPV1 channel. Intracellular calcium ([Ca(2+)]i) was detected using confocal fluorescence Ca(2+) imaging. [(3)H] thymidine incorporation and 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay were used to observe the DNA synthesis and proliferation. TUNEL assay was used to detect the apoptosis of ASMC.

RESULTS

(1) The expression of PCNA was significantly increased in intact asthmatic rat ASMC. (2) The expression of TRPV1 channel was significantly increased in asthmatic rat ASMC. (3) [Ca(2+)]i in ASMC of the asthmatic group was significantly increased. After treatment with TRPV1 agonist capsaicin (CAP), [Ca(2+)]i was further increased, whereas [Ca(2+)]i was decreased after administration of TRPV1 antagonist capsazepine (CPZ) in ASMC of the asthmatic group. (4) The DNA synthesis and absorbance of MTT were significantly increased, while apoptosis was significantly decreased in asthmatic ASMC. CAP further enhanced proliferation and decreased apoptosis. CPZ significantly inhibited the effect of CAP in asthmatic ASMC.

CONCLUSION

TRPV1 channel was involved in the regulation of proliferation and apoptosis in asthmatic ASMC.

Functionally important amino acid residues in the transient receptor potential vanilloid 1 (TRPV1) ion channel--an overview of the current mutational data

This review aims to create an overview of the currently available results of site-directed mutagenesis studies on transient receptor potential vanilloid type 1 (TRPV1) receptor. Systematization of the vast number of data on the functionally important amino acid mutations of TRPV1 may provide a clearer picture of this field, and may promote a better understanding of the relationship between the structure and function of TRPV1. The review summarizes information on 112 unique mutated sites along the TRPV1, exchanged to multiple different residues in many cases. These mutations influence the effect or binding of different agonists, antagonists, and channel blockers, alter the responsiveness to heat, acid, and voltage dependence, affect the channel pore characteristics, and influence the regulation of the receptor function by phosphorylation, glycosylation, calmodulin, PIP2, ATP, and lipid binding. The main goal of this paper is to publish the above mentioned data in a form that facilitates in silico molecular modelling of the receptor by promoting easier establishment of boundary conditions. The better understanding of the structure-function relationship of TRPV1 may promote discovery of new, promising, more effective and safe drugs for treatment of neurogenic inflammation and pain-related diseases and may offer new opportunities for therapeutic interventions.

Respiratory medicine in China: progress, challenges, and opportunities

The past century witnessed a rapid development of respiratory medicine in China. The major burden of respiratory disease has shifted from infectious diseases to chronic noninfectious diseases. Great achievements have been made in improving the national standard of clinical management of various respiratory diseases and in smoking control. The specialty of respiratory medicine is expanding into pulmonary and critical care medicine. Nevertheless, respiratory diseases remain a major public health problem, with new challenges such as air pollution and nosocomial infections. This review describes the history, accomplishments, new challenges, and opportunities in respiratory medicine in China.

Pathogenic role of store-operated and receptor-operated ca(2+) channels in pulmonary arterial hypertension

Pulmonary circulation is an important circulatory system in which the body brings in oxygen. Pulmonary arterial hypertension (PAH) is a progressive and fatal disease that predominantly affects women. Sustained pulmonary vasoconstriction, excessive pulmonary vascular remodeling, in situ thrombosis, and increased pulmonary vascular stiffness are the major causes for the elevated pulmonary vascular resistance (PVR) in patients with PAH. The elevated PVR causes an increase in afterload in the right ventricle, leading to right ventricular hypertrophy, right heart failure, and eventually death. Understanding the pathogenic mechanisms of PAH is important for developing more effective therapeutic approach for the disease. An increase in cytosolic free Ca²⁺ concentration ([Ca²⁺]_cyt) in pulmonary arterial smooth muscle cells (PASMC) is a major trigger for pulmonary vasoconstriction and an important stimulus for PASMC migration and proliferation which lead to pulmonary vascular wall thickening and remodeling. It is thus pertinent to define the pathogenic role of Ca²⁺ signaling in pulmonary vasoconstriction and PASMC proliferation to develop new therapies for PAH. [Ca²⁺]_cyt in PASMC is increased by Ca²⁺ influx through Ca²⁺ channels in the plasma membrane and by Ca²⁺ release or mobilization from the intracellular stores, such as sarcoplasmic reticulum (SR) or endoplasmic reticulum (ER). There are two Ca²⁺ entry pathways, voltage-dependent Ca²⁺ influx through voltage-dependent Ca²⁺ channels (VDCC) and voltage-independent Ca²⁺ influx through store-operated Ca²⁺ channels (SOC) and receptor-operated Ca²⁺ channels (ROC). This paper will focus on the potential role of VDCC, SOC, and ROC in the development and progression of sustained pulmonary vasoconstriction and excessive pulmonary vascular remodeling in PAH.

The functions of TRPA1 and TRPV1: moving away from sensory nerves

The transient receptor potential vanilloid 1 and ankyrin 1 (TRPV1 and TRPA1, respectively) channels are members of the TRP superfamily of structurally related, non-selective cation channels. It is rapidly becoming clear that the functions of TRPV1 and TRPA1 interlink with each other to a considerable extent. This is especially clear in relation to pain and neurogenic inflammation where TRPV1 is coexpressed on the vast majority of TRPA1-expressing sensory nerves and both integrate a variety of noxious stimuli. The more recent discovery that both TRPV1 and TRPA1 are expressed on a multitude of non-neuronal sites has led to a plethora of research into possible functions of these receptors. Non-neuronal cells on which TRPV1 and TRPA1 are expressed vary from vascular smooth muscle to keratinocytes and endothelium. This review will discuss the expression, functionality and roles of these non-neuronal TRP channels away from sensory nerves to demonstrate the diverse nature of TRPV1 and TRPA1 in addition to a direct role in pain and neurogenic inflammation.

Involvement of TRPV1 and TRPV4 channels in migration of rat pulmonary arterial smooth muscle cells

Pulmonary hypertension, the main disease of the pulmonary circulation, is characterized by an increase in pulmonary vascular resistance, involving proliferation and migration of pulmonary arterial smooth muscle cells (PASMC). However, cellular and molecular mechanisms underlying these phenomena remain to be identified. In the present study, we thus investigated in rat intrapulmonary arteries (1) the expression and the functional activity of TRPV1 and TRPV4, (2) the PASMC migration triggered by these TRPV channels, and (3) the associated reorganization of the cytoskeleton. Reverse transcriptase-polymerase chain reaction (RT-PCR) analysis demonstrated expression of TRPV1 and TRPV4 mRNA in rat intrapulmonary arteries. These results were confirmed at the protein level by western blot. Using microspectrofluorimetry (indo-1), we show that capsaicin and 4α-phorbol-12,13-didecanoate (4α-PDD), selective agonists of TRPV1 and TRPV4, respectively, increased the intracellular calcium concentration of PASMC. Furthermore, stimulation of TRPV1 and TRPV4 induced PASMC migratory responses, as assessed by two different methods (a modified Boyden chamber assay and a wound-healing migration assay). This response cannot seem to be attributed to a proliferative effect as assessed by BrdU and Wst-1 colorimetric methods. Capsaicin- and 4α-PDD-induced calcium and migratory responses were inhibited by the selective TRPV1 and TRPV4 blockers, capsazepine and HC067047, respectively. Finally, as assessed by immunostaining, these TRPV-induced migratory responses were associated with reorganization of the F-actin cytoskeleton and the tubulin and intermediate filament networks. In conclusion, these data point out, for the first time, the implication of TRPV1 and TRPV4 in rat PASMC migration, suggesting the implication of these TRPV channels in the physiopathology of pulmonary hypertension.

Differential effects of acute hypoxia on the activation of TRPV1 by capsaicin and acidic pH

Transient receptor potential vanilloid 1 (TRPV1) is a Ca(2+)-permeable cation channel activated by a variety of physicochemical stimuli. The effect of hypoxia (P(O(2)), 3%) on rat TRPV1 overexpressed in HEK293T has been studied. The basal TRPV1 current (I (TRPV1)) was partly activated by hypoxia, whereas capsaicin-induced TRPV1 (I (TRPV1,Cap)) was attenuated. Such changes were also suggested from hypoxia- and capsaicin-induced Ca(2+) signals in TRPV1-expressing cells. Regarding plausible changes of reactive oxygen species (ROS) under hypoxia, the effects of antioxidants, vitamin C and tiron, as membrane-impermeable and -permeable, respectively, were tested. Both I (TRPV1) and I (TRPV1,Cap) were increased by vitamin C, while only I (TRPV1) was slightly increased by tiron. The hypoxic inhibition of I (TRPV1,Cap) was still persistent under hypoxia/vitamin C. Interestingly, hypoxia/tiron strongly inhibited both I (TRPV1) and I (TRPV1,Cap). Also, with vitamin C applied through a pipette solution, hypoxia inhibited I (TRPV1) and I (TRPV1,Cap). In contrast, hypoxia and hypoxia/tiron had no effect on the I (TRPV1) induced by acid (pH 6.2, I (TRPV1,Acid)). Taken together, hypoxia partly activated TRPV1 while it decreased their sensitivity to capsaicin. Putative changes of ROS under hypoxia might underlie the side-specific effects of ROS on TRPV1: inhibitory at the extracellular and stimulatory at the intracellular side, respectively. The differential effects of hypoxia on I (TRPV1,Cap) and I (TRPV1,Acid) suggested that the intracellular ROS increase might attenuate the pharmacological potency of capsaicin.

Antioncogenic effects of transient receptor potential vanilloid 1 in the progression of transitional urothelial cancer of human bladder

The progression of normal cells to a tumorigenic and metastatic state involves the accumulation of mutations in multiple key signaling proteins, encoded by oncogenes and tumor suppressor genes. Recently, members of the TRP channel family have been included in the oncogenic and tumor suppressor protein family. TRPM1, TRPM8, and TRPV6 are considered to be tumor suppressors and oncogenes in localized melanoma and prostate cancer, respectively. Herein, we focus our attention on the antioncogenic properties of TRPV1. Changes in TRPV1 expression occur during the development of transitional cell carcinoma (TCC) of human bladder. A progressive decrease in TRPV1 expression as the TCC stage increases triggers the development of a more aggressive gene phenotype and invasiveness. Finally, downregulation of TRPV1 represents a negative prognostic factor in TCC patients. The knowledge of the mechanism controlling TRPV1 expression might improve the diagnosis and new therapeutic strategies in bladder cancer.

Insulin-secreting INS-1E cells express functional TRPV1 channels

We have studied whether functional TRPV1 channels exist in the INS-1E cells, a cell type used as a model for β-cells, and in primary β-cells from rat and human. The effects of the TRPV1 agonists capsaicin and AM404 on the intracellular free Ca (2+) concentration ([Ca (2+)]i) in the INS-1E cells were studied by fura-2 based microfluorometry. Capsaicin increased [Ca (2+)]i in a concentration-dependent manner, and the [Ca (2+)]i increase was dependent on extracellular Ca (2+). AM404 also increased [Ca (2+)]i in the INS-1E cells. Capsazepine, a specific antagonist of TRPV1, completely blocked the capsaicin- and AM404-induced [Ca (2+)]i increases. Capsaicin did not increase [Ca (2+)]i in the primary β-cells from rat and human. Whole cell patch clamp configuration was used to record currents across the plasma membrane in the INS-1E cells. Capsaicin elicited inward currents that were inhibited by capsazepine. Western blot analysis detected TRPV1 proteins in the INS-1E cells and the human islets. Immunohistochemistry was used to study the expression of TRPV1, but no TRPV1 protein immunoreactivity was detected in the human islet cells and the human insulinoma cells. We conclude that the INS-1E cells, but not the primary β-cells, express functional TRPV1 channels.

Role of thromboxane A2-activated nonselective cation channels in hypoxic pulmonary vasoconstriction of rat

Hypoxia-induced pulmonary vasoconstriction (HPV) is critical for matching of ventilation/perfusion in lungs. Although hypoxic inhibition of K+ channels has been a leading hypothesis for depolarization of pulmonary arterial smooth muscle cells (PASMCs) under hypoxia, pharmacological inhibition of K+ channels does not induce significant contraction in rat pulmonary arteries. Because a partial contraction by thromboxane A2 (TXA2) is required for induction of HPV, we hypothesize that TXA2 receptor (TP) stimulation might activate depolarizing nonselective cation channels (NSCs). Consistently, we found that 5–10 nM U46619, a stable agonist for TP, was indispensible for contraction of rat pulmonary arteries by 4-aminopyridine, a blocker of voltage-gated K+ channel (Kv). Whole cell voltage clamp with rat PASMC revealed that U46619 induced a NSC current ( INSC,TXA2) with weakly outward rectifying current-voltage relation. INSC,TXA2 was blocked by ruthenium red (RR), an antagonist of the transient receptor potential vanilloid-related channel (TRPV) subfamily. 2-Aminoethoxydiphenyl borate, an agonist for TRPV1–3, consistently activated NSC channels in PASMCs. In contrast, agonists for TRPV1 (capsaicin), TRPV3 (camphor), or TRPV4 (α-PDD) rarely induced an increase in the membrane conductance of PASMCs. RT-PCR analysis showed the expression of transcripts for TRPV2 and -4 in rat PASMCs. Finally, it was confirmed that pretreatment with RR largely inhibited HPV in the presence of U46619. The pretreatment with agonists for TRPV1 (capsaicin) and TRPV4 (α-PDD) was ineffective as pretone agents for HPV. Taken together, it is suggested that the concerted effects of INSC,TXA2 activation and Kv inhibition under hypoxia induce membrane depolarization sufficient for HPV. TRPV2 is carefully suggested as the TXA2-activated NSC in rat PASMC.

TRPV channels and vascular function

Transient receptor potential channels, of the vanilloid subtype (TRPV), act as sensory mediators, being activated by endogenous ligands, heat, mechanical and osmotic stress. Within the vasculature, TRPV channels are expressed in smooth muscle cells, endothelial cells, as well as in peri-vascular nerves. Their varied distribution and polymodal activation properties make them ideally suited to a role in modulating vascular function, perceiving and responding to local environmental changes. In endothelial cells, TRPV1 is activated by endocannabinoids, TRPV3 by dietary agonists and TRPV4 by shear stress, epoxyeicosatrienoic acids (EETs) and downstream of Gq-coupled receptor activation. Upon activation, these channels contribute to vasodilation via nitric oxide, prostacyclin and intermediate/small conductance potassium channel-dependent pathways. In smooth muscle, TRPV4 is activated by endothelial-derived EETs, leading to large conductance potassium channel activation and smooth muscle hyperpolarization. Conversely, smooth muscle TRPV2 channels contribute to global calcium entry and may aid constriction. TRPV1 and TRPV4 are expressed in sensory nerves and can cause vasodilation through calcitonin gene-related peptide and substance P release as well as mediating vascular function via the baroreceptor reflex (TRPV1) or via increasing sympathetic outflow during osmotic stress (TRPV4). Thus, TRPV channels play important roles in the regulation of normal and pathological cellular function in the vasculature.

Mice lacking functional TRPV1 are protected from pressure overload cardiac hypertrophy

TRPV1 (transient receptor potential cation channel, subfamily V, member 1) is best studied in peripheral sensory neurons as a pain receptor; however TRPV1 is expressed in numerous tissues and cell types including those of the cardiovascular system. TRPV1 expression is upregulated in the hypertrophic heart, and the channel is positioned to receive stimulatory signals in the hypertrophic heart. We hypothesized that TRPV1 has a role in regulating cardiac hypertrophy. Using transverse aortic constriction to model pressure overload cardiac hypertrophy we show that mice lacking functional TRPV1, compared to wild type, have improved heart function, and reduced hypertrophic, fibrotic and apoptotic markers. This suggests that TRPV1 plays a role in the progression of cardiac hypertrophy, and presents a possible therapeutic target for the treatment of cardiac hypertrophy and heart failure.

Modulation of urinary bladder innervation: TRPV1 and botulinum toxin A

The persisting interest around neurotoxins such as vanilloids and botulinum toxin (BoNT) derives from their marked effect on detrusor overactivity refractory to conventional antimuscarinic treatments. In addition, both are administered by intravesical route. This offers three potential advantages. First, intravesical therapy is an easy way to provide high concentrations of pharmacological agents in the bladder tissue without causing unsuitable levels in other organs. Second, drugs effective on the bladder, but inappropriate for systemic administration, can be safely used as it is the case of vanilloids and BoNT. Third, the effects of one single treatment might be extremely longlasting, contributing to render these therapies highly attractive to patients despite the fact that the reasons to the prolonged effect are still incompletely understood. Attractive as it may be, intravesical pharmacological therapy should still be considered as a second-line treatment in patients refractory to conventional oral antimuscarinic therapy or who do not tolerate its systemic side effects. However, the increasing off-label use of these neurotoxins justifies a reappraisal of their pharmacological properties.

Expression and physiological roles of TRP channels in smooth muscle cells

Smooth muscles are widely distributed in mammal body through various systems such as circulatory, respiratory, gastro-intestinal and urogenital systems. The smooth muscle cell (SMC) is not only a contractile cell but is able to perform other important functions such as migration, proliferation, production of cytokines, chemokines, extracellular matrix proteins, growth factors and cell surface adhesion molecules. Thus, SMC appears today as a fascinating cell with remarkable plasticity that contributes to its roles in physiology and disease. Most of the SMC functions are dependent on a key event: the increase in intracellular calcium concentration ([Ca(2+)](i)). Calcium entry from the extracellular space is a major step in the elevation of [Ca(2+)](i) in SMC and involves a variety of plasmalemmal calcium channels, among them is the superfamily of transient receptor potential (TRP) proteins. TRPC (canonical), TRPM (melastatin), TRPV (vanilloid) and TRPP (polycystin), are widely expressed in both visceral (airways, gastrointestinal tract, uterus) and vascular (systemic and pulmonary circulation) smooth muscles. Mainly, TRPC, TRPV and TRPM are implicated in a variety of physiological and pathophysiological processes such as: SMC contraction, relaxation, growth, migration and proliferation; control of blood pressure, arterial myogenic tone, pulmonary hypertension, intestinal motility, gastric acidity, uterine activity during parturition and labor. Thus it is becoming evident that TRP are major element of SMC calcium homeostasis and, thus, appear as novel drug targets for a better management of diseases originating from SMC dysfunction.

The calcium-sensing receptor mediates hypoxia-induced proliferation of rat pulmonary artery smooth muscle cells through MEK1/ERK1,2 and PI3K pathways

Activation of the calcium-sensing receptor (CaSR) leads to an increase of intracellular calcium concentration and alteration of cellular activities. High level of intracellular calcium is involved in hypoxia-induced proliferation of pulmonary arterial smooth muscle cells (PASMCs). However, whether the CaSR is expressed in PAMSCs and is related to the hypoxia-induced proliferation of PASMCs is unclear. In this study, the expression and distribution of CaSRs were detected by RT-PCR, western blotting and immunofluorescence; the intracellular concentration of free calcium ([Ca(2+) ](i) ) was determined by confocal laser scanning microscopy; cell proliferation was tested using an MTT and BrdU incorporation assay; cell cycle analysis was carried out using a flow cytometric assay; and the expression of proliferating cell nuclear antigen (PCNA), extracellular signal-regulated protein kinase 1,2 (ERK1,2) and AKT were analysed by western blotting. We observed that both CaSR mRNA and protein were expressed in rat PASMCs. Lowering of oxygen from 21% to 2.5% led to increased [Ca(2+) ](i) and CaSR expression. This condition of hypoxia also stimulated PASMCs proliferation accompanying with increased phosphorylation of ERK1,2 and AKT. GdCl(3) (an agonist of CaSR) or NPS2390 (an antagonist of CaSR) amplified or weakened the effect of hypoxia, respectively. PD98059 (a MEK1 inhibitor) or LY294002 (a PI3K inhibitors) decreased the up-regulation of PCNA expression and the increase of the cell proliferation index induced by hypoxia and GdCl(3) in PASMCs. Our results suggest that CaSR is expressed in rat PASMCs, and that CaSR activation through MEK1/ERK1,2 and PI3 kinase pathways is involved in hypoxia-induced proliferation of PASMCs.

Vanilloid and melastatin transient receptor potential channels in vascular smooth muscle

The mammalian transient receptor potential (TRP) superfamily consists of six subfamilies that are defined by structural homology: TRPC (conventional or canonical), TRPV (vanilloid), TRPM (melastatin), TRPA (ankyrin), TRPP (polycystin), and TRPML (mucoliptin). This review focuses on channels belonging to the vanilloid (V) and melastatin (M) TRP subfamilies. The TRPV subfamily consists of six members (TRPV1-6) and the TRPM subfamily has eight (TRPM1-8). The basic biophysical properties of these channels are briefly described. All of these channels except TRPV5, TRPV6, and TRPM1 are reportedly present in arterial smooth muscle from various segments of the vasculature. Studies demonstrating involvement of TRPV1, TRPV2, TRPV4, TRPM4, TRPM7, and TRPM8 in regulation of arterial smooth muscle function are reviewed. The functions of TRPV3, TRPM2, TRPM3, and TRPM6 channels in arterial myocytes have not been reported.

Expression of store-operated Ca2+ entry and transient receptor potential canonical and vanilloid-related proteins in rat distal pulmonary venous smooth muscle

Chronic hypoxia causes remodeling and alters contractile responses in both pulmonary arteries and pulmonary veins. Although pulmonary arteries have been studied extensively in these disorders, the mechanisms by which pulmonary veins respond to hypoxia and whether these responses contribute to chronic hypoxic pulmonary hypertension remain poorly understood. In pulmonary arterial smooth muscle, we have previously demonstrated that influx of Ca(2+) through store-operated calcium channels (SOCC) thought to be composed of transient receptor potential (TRP) proteins is likely to play an important role in development of chronic hypoxic pulmonary hypertension. To determine whether this mechanism could also be operative in pulmonary venous smooth muscle, we measured intracellular Ca(2+) concentration ([Ca(2+)](i)) by fura-2 fluorescence microscopy in primary cultures of pulmonary venous smooth muscle cells (PVSMC) isolated from rat distal pulmonary veins. In cells perfused with Ca(2+)-free media containing cyclopiazonic acid (10 μM) and nifedipine (5 μM) to deplete sarcoplasmic reticulum Ca(2+) stores and block voltage-dependent Ca(2+) channels, restoration of extracellular Ca(2+) (2.5 mM) caused marked increases in [Ca(2+)](i), whereas MnCl(2) (200 μM) quenched fura-2 fluorescence, indicating store-operated Ca(2+) entry (SOCE). SKF-96365 and NiCl(2), antagonists of SOCC, blocked SOCE at concentrations that did not alter Ca(2+) responses to 60 mM KCl. Of the seven known canonical TRP (TRPC1-7) and six vanilloid-related TRP channels (TRPV1-6), real-time PCR revealed mRNA expression of TRPC1 > TRPC6 > TRPC4 > TRPC2 ≈ TRPC5 > TRPC3, TRPV2 > TRPV4 > TRPV1 in distal PVSMC, and TRPC1 > TRPC6 > TRPC3 > TRPC4 ≈ TRPC5, TRPV2 ≈ TRPV4 > TRPV1 in rat distal pulmonary vein (PV) smooth muscle. Western blotting confirmed protein expression of TRPC1, TRPC6, TRPV2, and TRPV4 in both PVSMC and PV. Our results suggest that SOCE through Ca(2+) channels composed of TRP proteins may contribute to Ca(2+) signaling in rat distal PV smooth muscle.

Pulmonary hypertension in China: pulmonary vascular disease: the global perspective

Significant progress has been made in understanding the pathogenesis of pulmonary hypertension (PH) and developing therapeutic approaches for PH in recent years. Most of the currently available data regarding the prevalence, diagnosis, treatment, and prognosis of PH are from American and European populations. Whether these data are also valid in the Chinese population is still controversial. China has a relatively large population of patients with PH for clinical and basic research. However, many medical centers and hospitals in China have limited experience with PH diagnosis and treatment. Given the potential higher prevalence of PH in China than in the United States and European countries, it is critical to develop suitable, effective, and novel therapeutic approaches for Chinese patients. Measures for the detection and prevention of PH need to be put in place urgently for the management of PH in China.