Recent developments in vascular endothelial cell transient receptor potential channels

Piperine, a dietary phytochemical, inhibits angiogenesis

Angiogenesis plays an important role in tumor progression. Piperine, a major alkaloid constituent of black pepper, has diverse physiological actions including killing of cancer cells; however, the effect of piperine on angiogenesis is not known. Here we show that piperine inhibited the proliferation and G(1)/S transition of human umbilical vein endothelial cells (HUVECs) without causing cell death. Piperine also inhibited HUVEC migration and tubule formation in vitro, as well as collagen-induced angiogenic activity by rat aorta explants and breast cancer cell-induced angiogenesis in chick embryos. Although piperine binds to and activates the cation channel transient receptor potential vanilloid 1 (TRPV1), its effects on endothelial cells did not involve TRPV1 since the antiproliferative effect of piperine was not affected by TRPV1-selective antagonists, nor did HUVECs express detectable TRPV1 mRNA. Importantly, piperine inhibited phosphorylation of Ser 473 and Thr 308 residues of Akt (protein kinase B), which is a key regulator of endothelial cell function and angiogenesis. Consistent with Akt inhibition as the basis of piperine's action on HUVECs, inhibition of the phosphoinositide-3 kinase/Akt signaling pathway with LY-294002 also inhibited HUVEC proliferation and collagen-induced angiogenesis. Taken together, these data support the further investigation of piperine as an angiogenesis inhibitor for use in cancer treatment.

TRP channels: sensors and transducers of gasotransmitter signals

The transient receptor potential (trp) gene superfamily encodes cation channels that act as multimodal sensors for a wide variety of stimuli from outside and inside the cell. Upon sensing, they transduce electrical and Ca²⁺ signals via their cation channel activities. These functional features of TRP channels allow the body to react and adapt to different forms of environmental changes. Indeed, members of one class of TRP channels have emerged as sensors of gaseous messenger molecules that control various cellular processes. Nitric oxide (NO), a vasoactive gaseous molecule, regulates TRP channels directly via cysteine (Cys) S-nitrosylation or indirectly via cyclic GMP (cGMP)/protein kinase G (PKG)-dependent phosphorylation. Recent studies have revealed that changes in the availability of molecular oxygen (O₂) also control the activation of TRP channels. Anoxia induced by O₂-glucose deprivation and severe hypoxia (1% O₂) activates TRPM7 and TRPC6, respectively, whereas TRPA1 has recently been identified as a novel sensor of hyperoxia and mild hypoxia (15% O₂) in vagal and sensory neurons. TRPA1 also detects other gaseous molecules such as hydrogen sulfide (H₂S) and carbon dioxide (CO₂). In this review, we focus on how signaling by gaseous molecules is sensed and integrated by TRP channels.

Update on vascular endothelial Ca2+ signalling: A tale of ion channels, pumps and transporters

A monolayer of endothelial cells (ECs) lines the lumen of blood vessels and forms a multifunctional transducing organ that mediates a plethora of cardiovascular processes. The activation of ECs from as state of quiescence is, therefore, regarded among the early events leading to the onset and progression of potentially lethal diseases, such as hypertension, myocardial infarction, brain stroke, and tumor. Intracellular Ca²⁺ signals have long been know to play a central role in the complex network of signaling pathways regulating the endothelial functions. Notably, recent work has outlined how any change in the pattern of expression of endothelial channels, transporters and pumps involved in the modulation of intracellular Ca²⁺ levels may dramatically affect whole body homeostasis. Vascular ECs may react to both mechanical and chemical stimuli by generating a variety of intracellular Ca²⁺ signals, ranging from brief, localized Ca²⁺ pulses to prolonged Ca²⁺ oscillations engulfing the whole cytoplasm. The well-defined spatiotemporal profile of the subcellular Ca²⁺ signals elicited in ECs by specific extracellular inputs depends on the interaction between Ca²⁺ releasing channels, which are located both on the plasma membrane and in a number of intracellular organelles, and Ca²⁺ removing systems. The present article aims to summarize both the past and recent literature in the field to provide a clear-cut picture of our current knowledge on the molecular nature and the role played by the components of the Ca²⁺ machinery in vascular ECs under both physiological and pathological conditions.

Mechanoregulation of cytoskeletal dynamics by TRP channels

The ability of cells to respond to mechanical stimulation is crucial to a variety of biological processes, including cell migration, axonal outgrowth, perception of pain, cardiovascular responses and kidney physiology. The translation of mechanical cues into cellular responses, a process known as mechanotransduction, typically takes place in specialized multiprotein structures such as cilia, cell-cell or cell-matrix adhesions. Within these structures, mechanical forces such as shear stress and membrane stretch activate mechanosensitive proteins, which set off a series of events that lead to altered cell behavior. Members of the transient receptor potential (TRP) family of cation channels are emerging as important players in mechanotransductory pathways. Localized within mechanosensory structures, they are activated by mechanical stimuli and trigger fast as well as sustained cytoskeletal responses. In this review, we will provide an overview of how TRP channels affect cytoskeletal dynamics in various mechano-regulated processes.

Transient receptor potential canonical type 3 channels facilitate endothelium-derived hyperpolarization-mediated resistance artery vasodilator activity

AIMS

Microdomain signalling mechanisms underlie key aspects of artery function and the modulation of intracellular calcium, with transient receptor potential (TRP) channels playing an integral role. This study determines the distribution and role of TRP canonical type 3 (C3) channels in the control of endothelium-derived hyperpolarization (EDH)-mediated vasodilator tone in rat mesenteric artery.

METHODS AND RESULTS

TRPC3 antibody specificity was verified using rat tissue, human embryonic kidney (HEK)-293 cells stably transfected with mouse TRPC3 cDNA, and TRPC3 knock-out (KO) mouse tissue using western blotting and confocal and ultrastructural immunohistochemistry. TRPC3-Pyr3 (ethyl-1-(4-(2,3,3-trichloroacrylamide)phenyl)-5-(trifluoromethyl)-1H-pyrazole-4-carboxylate) specificity was verified using patch clamp of mouse mesenteric artery endothelial and TRPC3-transfected HEK cells, and TRPC3 KO and wild-type mouse aortic endothelial cell calcium imaging and mesenteric artery pressure myography. TRPC3 distribution, expression, and role in EDH-mediated function were examined in rat mesenteric artery using immunohistochemistry and western blotting, and pressure myography and endothelial cell membrane potential recordings. In rat mesenteric artery, TRPC3 was diffusely distributed in the endothelium, with approximately five-fold higher expression at potential myoendothelial microdomain contact sites, and immunoelectron microscopy confirmed TRPC3 at these sites. Western blotting and endothelial damage confirmed primary endothelial TRPC3 expression. In rat mesenteric artery endothelial cells, Pyr3 inhibited hyperpolarization generation, and with individual SK(Ca) (apamin) or IK(Ca) (TRAM-34) block, Pyr3 abolished the residual respective IK(Ca)- and SK(Ca)-dependent EDH-mediated vasodilation.

CONCLUSION

The spatial localization of TRPC3 and associated channels, receptors, and calcium stores are integral for myoendothelial microdomain function. TRPC3 facilitates endothelial SK(Ca) and IK(Ca) activation, as key components of EDH-mediated vasodilator activity and for regulating mesenteric artery tone.

Transient receptor potential vanilloid type 1 channels contribute to reflex cutaneous vasodilation in humans

Mechanisms underlying the cutaneous vasodilation in response to an increase in core temperature remain unresolved. The purpose of this study was to determine a potential contribution of transient receptor potential vanilloid type 1 (TRPV-1) channels to reflex cutaneous vasodilation. Twelve subjects were equipped with four microdialysis fibers on the ventral forearm, and each site randomly received 1) 90% propylene glycol + 10% lactated Ringer (vehicle control); 2) 10 mM l-NAME; 3) 20 mM capsazepine to inhibit TRPV-1 channels; 4) combined 10 mM l-NAME + 20 mM capsazepine. Whole body heating was achieved via water-perfused suits sufficient to raise oral temperature at least 0.8°C above baseline. Maximal skin blood flow was achieved by local heating to 43°C and infusion of 28 mM nitroprusside. Systemic arterial pressure (SAP) was measured, and skin blood flow was monitored via laser-Doppler flowmetry (LDF). Cutaneous vascular conductance (CVC) was calculated as LDF/SAP and normalized to maximal vasodilation (%CVC(max)). Capsazepine sites were significantly reduced compared with control (50 ± 4%CVC(max) vs. 67 ± 5%CVC(max), respectively; P < 0.05). l-NAME (33 ± 3%CVC(max)) and l-NAME + capsazepine (30 ± 4%CVC(max)) sites were attenuated compared with control (P < 0.01) and capsazepine (P < 0.05); however, there was no difference between l-NAME and combined l-NAME + capsazepine. These data suggest TRPV-1 channels participate in reflex cutaneous vasodilation and TRPV-1 channels may account for a portion of the NO component. TRPV-1 channels may have a direct neural contribution or have an indirect effect via increased arterial blood temperature. Whether the TRPV-1 channels directly or indirectly contribute to reflex cutaneous vasodilation remains uncertain.

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.

Ca2+-activated K+ channels of small and intermediate conductance control eNOS activation through NAD(P)H oxidase

Ca(2+)-activated K(+) channels (K(Ca)) and NO play a central role in the endothelium-dependent control of vasomotor tone. We evaluated the interaction of K(Ca) with NO production in isolated arterial mesenteric beds of the rat. In phenylephrine-contracted mesenteries, acetylcholine (ACh)-induced vasodilation was reduced by NO synthase (NOS) inhibition with N(ω)-nitro-L-arginine (L-NA), but in the presence of tetraethylammonium, L-NA did not further affect the response. In KCl-contracted mesenteries, the relaxation elicited by 100 nM ACh or 1 μM ionomycin was abolished by L-NA, tetraethylammonium, or simultaneous blockade of small-conductance K(Ca) (SK(Ca)) channels with apamin and intermediate-conductance K(Ca) (IK(Ca)) channels with triarylmethane-34 (TRAM-34). Apamin-TRAM-34 treatment also abolished 100 nM ACh-activated NO production, which was associated with an increase in superoxide formation. Endothelial cell Ca(2+) buffering with BAPTA elicited a similar increment in superoxide. Apamin-TRAM-34 treatment increased endothelial NOS phosphorylation at threonine 495 (P-eNOS(Thr495)). Blockade of NAD(P)H oxidase with apocynin or superoxide dismutation with PEG-SOD prevented the increment in superoxide and changes in P-eNOS(Thr495) observed during apamin and TRAM-34 application. Our results indicate that blockade of SK(Ca) and IK(Ca) activates NAD(P)H oxidase-dependent superoxide formation, which leads to inhibition of NO release through P-eNOS(Thr495). These findings disclose a novel mechanism involved in the control of NO production.

Transient receptor potential channel activation and endothelium-dependent dilation in the systemic circulation

The endothelium plays a crucial role in the regulation of vascular tone by releasing a number of vasodilator mediators, including nitric oxide, prostacyclin, and endothelium-derived hyperpolarizing factor(s). The production of these mediators is typically initiated by an increase in intracellular Ca(2+) concentration ([Ca(2+)]i) in endothelial cells. An essential component of this Ca(2+) signal is the entry of Ca(2+) from the extracellular space through plasma membrane Ca(2+)-permeable channels. Although the molecular identification of the potential Ca(2+) entry channel(s) responsible for the release of endothelial relaxing factors is still evolving, accumulating evidence indicates that the transient receptor potential (TRP) channels, a superfamily of Ca(2+)-permeable cation channels, serve as an important mechanism of Ca(2+) entry in endothelial cells and other nonexcitable cells. The activation of these channels has been implicated in diverse endothelial functions ranging from control of vascular tone and regulation of vascular permeability to angiogenesis and vascular remodeling. This review summarizes recent evidence concerning TRP channels and endothelium-dependent dilation in several systemic vascular beds. In particular, we highlight the emerging roles of several TRP channels from the canonical and vanilloid subfamilies, including TRPV4, TRPC4, and TRPC6, in vasodilatory responses to shear stress and receptor agonists and discuss potential signaling mechanisms linking the TRP channel activation and the initiation of endothelium-derived hyperpolarizing factor-mediated responses in endothelial cells.

Hypoxic stress induces transient receptor potential melastatin 2 (TRPM2) channel expression in adult rat cardiac fibroblasts

When cardiac tissue is exposed to hypoxia, myocytes are damaged, while fibroblasts are activated. However, it is unknown what changes are induced by hypoxia in cardiac fibroblasts. In this study, using the whole cell patch-clamp technique, we investigated the effect of hypoxia on membrane currents in fibroblasts primarily cultured from adult rat hearts. Cardiac fibroblasts were incubated for 24 h under normoxic or hypoxic conditions using Anaeropack. Hypoxia increased a current which reversed at around -20 mV in the cardiac fibroblasts. This current was inhibited by clotrimazole, which is an inhibitor of transient receptor potential melastatin 2 (TRPM2) channel and intermediate-conductance Ca(2+)-activated K(+) channel (KCa3.1). ADP ribose in the pipette solution enhanced this current. Quantitative RT-PCR revealed that mRNA of TRPM2, but not that of KCa3.1, was increased by hypoxia. RNA interference of TRPM2 prevented the development of the hypoxia-induced current. H(2)O(2), an activator of TRPM2 channel, induced a higher [Ca(2+)](i) elevation in hypoxia-exposed cardiac fibroblasts than that in normoxia-exposed cells. We conclude that hypoxia induces TRPM2 channel expression in adult rat cardiac fibroblasts.

Canonical transient receptor potential channels in diabetes

Canonical transient receptor potential (TRPC) channel proteins have been identified as downstream molecules in a G protein-coupled receptor signaling pathway and are involved in a variety of cell functions due to their ability to regulate intracellular calcium signaling. TRPC channel physiology has been an increasingly interesting and relevant topic over the last decade, and the outcomes from various studies have advanced our understanding of TRPC function in the normal state. Recently, attention has turned to whether or not TRPC proteins are implicated in diseases. Emerging evidence suggests a significant contribution of several isoforms of TRPC proteins to cardiovascular as well as renal diseases. This review focuses on the implication of TRPC proteins as they pertain to diabetes. We summarize the recent findings by other investigators as well as ourselves and additionally discuss the important role of TRPC proteins in the development of various diabetic complications, such as diabetic nephropathy and diabetic vasculopathy. The underlying mechanisms which contribute to these complications are also outlined. Lastly, we elaborate on the role of TRPC proteins as a potential therapeutic target for treating diabetes-associated diseases.

Transient receptor potential canonical channels in angiogenesis and axon guidance

Wiring of vascular and neural networks requires precise guidance of growing blood vessels and axons, respectively, to reach their targets during development. Both of the processes share common molecular signaling pathways. Transient receptor potential canonical (TRPC) channels are calcium-permeable cation channels and gated via receptor- or store-operated mechanisms. Recent studies have revealed the requirement of TRPC channels in mediating guidance cue-induced calcium influx and their essential roles in regulating axon navigation and angiogenesis. Dissecting TRPC functions in these physiological processes may provide therapeutic implications for suppressing pathological angiogenesis and improving nerve regeneration.

Thrombospondin-1 triggers cell migration and development of advanced prostate tumors

The antitumor effects of pharmacologic inhibitors of angiogenesis are hampered in patients by the rapid development of tumor resistance, notably through increased invasiveness and accelerated metastasis. Here, we reevaluated the role of the endogenous antiangiogenic thrombospondin 1 (TSP1) in prostate carcinomas in which angiogenesis is an active process. In xenografted tumors, we observed that TSP1 altogether inhibited angiogenesis and fostered tumor development. Our results show that TSP1 is a potent stimulator of prostate tumor cell migration. This effect required CD36, which also mediates TSP1 antiangiogenic activity, and was mimicked by an antiangiogenic TSP1-derived peptide. As suspected for pharmacologic inhibitors of angiogenesis, the TSP1 capacities to increase hypoxia and to trigger cell migration are thus inherently linked. Importantly, although antiangiogenic TSP1 increases hypoxia in vivo, our data show that, in turn, hypoxia induced TSP1, thus generating a vicious circle in prostate tumors. In radical prostatectomy specimens, we found TSP1 expression significantly associated with invasive tumors and with tumors which eventually recurred. TSP1 may thus help select patients at risk of prostate-specific antigen relapse. Together, the data suggest that intratumor disruption of the hypoxic cycle through TSP1 silencing will limit tumor invasion.

Calcium and electrical signalling along endothelium of the resistance vasculature

This MiniReview is focused on the nature of intercellular signalling along the endothelium that helps to co-ordinate blood flow control in vascular resistance networks. Vasodilation initiated by contracting skeletal muscle ascends from arterioles within the tissue to encompass resistance arteries upstream and thereby increase blood flow during exercise. In resistance vessels, acetylcholine microiontophoresis or intracellular current injection initiates hyperpolarization that conducts through gap junction channels (GJCs) along the vessel wall resulting in conducted vasodilation (CVD). Both ascending vasodilation and CVD are eliminated with endothelial cell (EC) disruption, pointing to common signalling events and mutual dependence upon EC integrity. As demonstrated by electrical coupling and dye transfer during intracellular recording, their longitudinal orientation and robust expression of GJCs enable ECs to play a predominant role in CVD. Once conduction is initiated, a major interest centres on whether CVD is purely passive or involves additional 'active' signalling events. Here, we discuss components for Ca²⁺ and electrical signalling with an emphasis on intercellular coupling through endothelial GJCs. We stress the importance of understanding relationships between intracellular Ca²⁺ dynamics, EC hyperpolarization and CVD while integrating findings from isolated ECs into more complex interactions in vivo. Whereas endothelial dysfunction accompanies cardiovascular disease and the components of intra- and inter-cellular signalling are increasingly well defined, little is known of how Ca²⁺ signalling and electrical conduction along microvascular endothelium are altered in diseased states. Thus, greater insight into how these relationships are governed and interact is a key goal for continued research efforts.

TRP-channel-specific cutaneous eicosanoid release patterns

Analyzing mechanisms and key players in peripheral nociception nonneuronal skin cells are getting more and more into focus. Herein we investigated the functional expression of TRPV1 and TRPA1 in human keratinocytes and fibroblasts and assessed proinflammatory lipid mediator release upon their stimulation as well as sensory effects after topical application, combining in vitro and in vivo approaches. In vitro, the expression of functional TRPV1 and TRPA1 channels on fibroblasts and keratinocytes was confirmed via immunofluorescence, qualitative real time (RT) polymerase chain reaction, and cellular Ca(2+) influx measurements. Additionally, the agonists allyl isothiocyanate (TRPA1) and capsaicin (TRPV1) induce a differential secretion pattern of the eicosanoids PGE(2) and LTB(4) in human dermal fibroblasts and keratinocytes, which was also detectable invivo, analyzing suction blister fluid at various times after short-term topical application. Capsaicin provoked the release of LTB(4) at 2 and 24 hours. In contrast, PGE(2) levels were reduced upon stimulation. Allyl isothiocyanate, however, increased PGE(2) levels only at 24 hours, but did not alter LTB(4) levels. In parallel, heat pain thresholds were reduced by both agents after short-term topical application, but only AITC provoked a long-lasting local erythema. In conclusion, the agonist-induced activation of nociceptors by TRPA1 and TRPV1 elicits painful sensations, whereas nonneuronal tissue cells respond with differential release of inflammatory mediators, thus influencing local vasodilatation and neuronal sensitization. These results have implications for the application of transient receptor potential antagonists to improve inflammatory skin conditions and pain management.

Endothelin-mediated in vivo pressor responses following TRPV1 activation

Transient receptor potential vanilliod 1 (TRPV1) channels have recently been postulated to play a role in the vascular complications/consequences associated with diabetes despite the fact that the mechanisms through which TRPV1 regulates vascular function are not fully known. Accordingly, our goal was to define the mechanisms by which TRPV1 channels modulate vascular function and contribute to vascular dysfunction in diabetes. We subjected mice lacking TRPV1 [TRPV1(−/−)], db/ db, and control C57BLKS/J mice to in vivo infusion of the TRPV1 agonist capsaicin or the α-adrenergic agonist phenylephrine (PE) to examine the integrated circulatory actions of TRPV1. Capsaicin (1, 10, 20, and 100 μg/kg) dose dependently increased MAP in control mice (5.7 ± 1.6, 11.7 ± 2.1, 25.4 ± 3.4, and 51.6 ± 3.9%), which was attenuated in db/db mice (3.4 ± 2.1, 3.9 ± 2.1, 7.0 ± 3.3, and 17.9 ± 6.2%). TRPV1(−/−) mice exhibited no changes in MAP in response to capsaicin, suggesting the actions of this agonist are specific to TRPV1 activation. Immunoblot analysis revealed decreased aortic TRPV1 protein expression in db/db compared with control mice. Capsaicin-induced responses were recorded following inhibition of endothelin A and B receptors (ETA /ETB). Inhibition of ETA receptors abolished the capsaicin-mediated increases in MAP. Combined antagonism of ETA and ETB receptors did not further inhibit the capsaicin response. Cultured endothelial cell exposure to capsaicin increased endothelin production as shown by an endothelin ELISA assay, which was attenuated by inhibition of TRPV1 or endothelin-converting enzyme. TRPV1 channels contribute to the regulation of vascular reactivity and MAP via production of endothelin and subsequent activation of vascular ETA receptors. Impairment of TRPV1 channel function may contribute to vascular dysfunction in diabetes.

Ion channels and transporters in cancer. 6. Vascularizing the tumor: TRP channels as molecular targets

Tumor vascularization is a critical process that determines tumor growth and metastasis. In the last decade new experimental evidence obtained from in vitro and in vivo studies have challenged the classical angiogenesis model forcing us to consider new scenarios for tumor neovascularization. In particular, the genetic stability of tumor-derived endothelial cells (TECs) has been recently questioned in several studies, which show that TECs, as well as pericytes, differ significantly from their normal counterparts at genetic and functional levels. In addition to such an epigenetic action of tumor microenvironment on endothelial cells (ECs) commitment, the distinct characteristics of TECs could be due to differences in their origin compared with preexisting differentiated ECs. Intracellular Ca(2+) signals are involved at different critical phases in the regulation of the complex process of angiogenesis and tumor progression. These signals are generated by a wide variety of intrinsic and extrinsic factors. Several key components of Ca(2+) signaling including Ca(2+) channels in the plasma membrane, endoplasmic reticulum, calcium pumps, and mitochondria contribute to the generation, amplitude, and frequency of these Ca(2+) change. In particular, several members of the transient receptor potential (TRP) family of calcium-permeable channels have profound effects on the function of ECs. Because of its multifaceted role in the control of cell function, proliferation, and motility, TRP channels have been suggested as a potential molecular target for control of tumor neovascularization. Since plasma membrane Ca(2+) channels are easily and directly accessible via the bloodstream, they are potential targets for a number of pharmacological and antibody-targeted therapeutic strategies, with specificity being the main limitation. In this review we discuss recent advances in understanding the role of Ca(2+) channels, with specific reference to TRP channels, in tumor vascularization process.

Caveolae create local signalling domains through their distinct protein content, lipid profile and morphology

Compartmentation of signalling allows multiple stimuli to achieve diverse cellular responses with only a limited pool of second messengers. This spatial control of signalling is achieved, in part, by cellular structures which bring together elements of a particular cascade. One such structure is the caveola, a flask-shaped lipid raft. Caveolae are well-recognised as signalosomes, platforms for assembly of signalling complexes of receptors, effectors and their targets, which can facilitate efficient and specific cellular responses. Here we extend this simple model and present evidence to show how the protein and lipid profiles of caveolae, as well as their characteristic morphology, define their roles in creating local signalling domains in the cardiac myocyte. This article is part of a Special Issue entitled "Local Signaling in Myocytes."

Thermosensitive transient receptor potential channels in human corneal epithelial cells

Thermosensitive transient receptor potential (TRP) proteins such as TRPV1-TRPV4 are all heat-activated non-selective cation channels that are modestly permeable to Ca(2+). TRPV1, TRPV3, and TRPV4 functional expression were previously identified in human corneal epithelial cells (HCEC). However, the membrane currents were not described underlying their activation by either selective agonists or thermal variation. This study characterized the membrane currents and [Ca(2+)](i) transients induced by thermal and agonist TRPV1 and 4 stimulation. TRPV1 and 4 expressions were confirmed by RT-PCR and TRPV2 transcripts were also detected. In fura2-loaded HCEC, a TRPV1-3 selective agonist, 100 µM 2-aminoethoxydiphenyl borate (2-APB), induced intracellular Ca(2+) transients and an increase in non-selective cation outward currents that were suppressed by ruthenium-red (RuR) (10-20 µM), a non-selective TRPV channel blocker. These changes were also elicited by rises in ambient temperature from 25 to over 40 °C. RuR (5 µM) and a selective TRPV1 channel blocker capsazepine CPZ (10 µM) or another related blocker, lanthanum chloride (La(3+)) (100 µM) suppressed these temperature-induced Ca(2+) increases. Planar patch-clamp technique was used to characterize the currents underlying Ca(2+) transients. Increasing the temperature to over 40 °C induced reversible rises in non-selective cation currents. Moreover, a hypotonic challenge (25%) increased non-selective cation currents confirming TRPV4 activity. We conclude that HCEC possess in addition to thermosensitive TRPV3 activity TRPV1, TRPV2, and TRPV4 activity. Their activation confers temperature sensitivity at the ocular surface, which may protect the cornea against such stress.

Transient receptor potential vanilloid type-1 (TRPV-1) channels contribute to cutaneous thermal hyperaemia in humans

The initial, rapid increase in skin blood flow in response to direct application of heat is thought to be mediated by an axon reflex, which is dependent on intact cutaneous sensory nerves. We tested the hypothesis that inhibition of transient receptor potential vanilloid type 1 (TRPV-1) channels, which are putative channels located on sensory nerves, would attenuate the skin blood flow response to local heating in humans. Ten subjects were equipped with four microdialysis fibres which were randomly assigned one of four treatments: (1) vehicle control (90% propylene glycol + 10% lactated Ringer solution); (2) 20 mm capsazepine to inhibit TRPV-1 channels; (3) 10 mm l-NAME to inhibit NO synthase; and (4) combined 20 mm capsazepine + 10 mm l-NAME. Following baseline measurements, the temperature of skin heaters was increased from 33°C to 42°C at a rate of 1.0°C every 10 s and local temperature was held at 42°C for 20-30 min until a stable plateau in skin blood flow was achieved. An index of skin blood flow was measured directly over each microdialysis site via laser-Doppler flowmetry (LDF). Beat-by-beat blood pressure was measured via photoplethysmography and verified via automated brachial auscultation. At the end of the local heating protocol, temperature of the heaters was increased to 43°C and 28 mm nitroprusside was infused to achieve maximal vasodilatation. Cutaneous vascular conductance (CVC) was calculated as LDF/mean arterial pressure and normalized to maximal values (%CVCmax). Initial peak in capsazepine (44 ± 4%CVCmax), l-NAME (56 ± 4%CVCmax) and capsazepine + l-NAME (32 ± 6%CVCmax) sites was significantly attenuated compared to control (87 ± 5%CVCmax; P < 0.001 for all conditions). The plateau phase of thermal hyperaemia was significantly attenuated in capsazepine (73 ± 6%CVCmax), l-NAME (47 ± 5%CVCmax) and capsazepine + l-NAME (31 ± 7%CVCmax) sites compared to control (92 ± 5%CVCmax; P < 0.001 for all conditions). These data suggest TRPV-1 channels contribute substantially to the initial peak and modestly to the plateau phases of thermal hyperaemia. These data further suggest a portion of the NO component of thermal hyperaemia may be due to activation of TRPV-1 channels.

Cerebral arteriogenesis is enhanced by pharmacological as well as fluid-shear-stress activation of the Trpv4 calcium channel

OBJECTIVES

This study aimed to determine the importance of the shear-stress-sensitive calcium channels Trpc1, Trpm7, Trpp2, Trpv2 (transient receptor potential cation channel, subfamily V, member 2) and Trpv4 for cerebral arteriogenesis. The expression profiles were analysed, comparing the stimulation of collateral growth by target-specific drugs to that achieved by maximum increased fluid shear stress (FSS).

DESIGN

A prospective, controlled study wherein rats were subjected to bilateral carotid artery ligature (BCL), or BCL + arteriovenous fistula, or BCL + drug application.

METHODS

Messenger RNA (mRNA) abundance and protein expression were determined in FSS-stimulated cerebral collaterals by quantitative real-time polymerase chain reaction (qRT-PCR) and immunohistochemistry. Drugs were applied via osmotic mini pumps and arteriogenesis was evaluated by post-mortem angiograms and Ki67 immunostaining.

RESULTS

Trpv4 was the only mechanosensitive Trp channel showing significantly increased mRNA abundance and protein expression after FSS stimulation. Activation of Trpv4 by 4α-phorbol-12,13-didecanoate caused significantly enhanced collateral growth (length: 4.43 ± 0.20 mm and diameter: 282.6 ± 8.1 μm) compared with control (length: 3.80 ± 0.06 mm and diameter: 237.3 ± 5.3 μm). Drug application stimulated arteriogenesis to almost the same extent as did maximum FSS stimulation (length: 4.61 ± 0.07 mm and diameter: 327.4 ± 12.6 μm).

CONCLUSIONS

Trpv4 showed significantly increased expression in FSS-stimulated cerebral collaterals. Pharmacological Trpv4 activation enhanced cerebral arteriogenesis, pinpointing Trpv4 as a possible candidate for the development of new therapeutic concepts.

TRP channels in vascular endothelial cells

Endothelial cells regulate multiple vascular functions, such as vascular tone, permeability, remodeling, and angiogenesis. It is known for long that cytosolic Ca(2+) level ([Ca(2+)](i)) and membrane potential of endothelial cells are crucial factors to initiate the signal transduction cascades, leading to diverse vascular functions. Among the various kinds of endothelial ion channels that regulate ion homeostasis, transient receptor potential (TRP) channels emerge as the prime mediators for a diverse range of vascular signaling. The characteristics of TRP channels, including subunit heteromultimerization, diverse ion selectivity, and multiple modes of activation, permit their versatile functional roles in vasculatures. Substantial amount of evidence demonstrates that many TRP channels in endothelial cells participate in physiological and pathophysiological processes of vascular system. In this article, we summarize the recent findings of TRP research in endothelial cells, aiming at providing up-to-date information to the researchers in this rapidly growing field.

TRPM channels in the vasculature

Recent studies show that mammalian melastatin TRPM nonselective cation channels (TRPM1-8), members of the largest and most diverse TRP subfamily, are widely expressed in the endothelium and vascular smooth muscles. When activated, these channels similarly to other TRPs permit the entry of sodium, calcium and magnesium, thus causing membrane depolarisation. Although membrane depolarisation reduces the driving force for calcium entry via TRPMs as well as other pathways for calcium entry, in smooth muscle myocytes expressing voltage-gated Ca(2+) channels the predominant functional effect is an increase in intracellular Ca(2+) concentration and myocyte contraction. This review focuses on several best documented aspects of vascular functions of TRPMs, including the role of TRPM2 in oxidant stress, regulation of endothelial permeability and cell death, the connection between TRPM4 and myogenic response, significance of TRPM7 for magnesium homeostasis, vessel injury and hypertension, and emerging evidence that the cold and menthol receptor TRPM8 is involved in the regulation of vascular tone.

The mechanism of agonist induced Ca2+ signalling in intact endothelial cells studied confocally in in situ arteries

In endothelial cells there remain uncertainties in the details of how Ca²⁺ signals are generated and maintained, especially in intact preparations. In particular the role of the sarco-endoplasmic reticulum Ca²⁺-ATPase (SERCA), in contributing to the components of agonist-induced signals is unclear.

The aim of this work was to increase understanding of the detailed mechanism of Ca²⁺ signalling in endothelial cells using real time confocal imaging of Fluo-4 loaded intact rat tail arteries in response to muscarinic stimulation. In particular we have focused on the role of SERCA, and its interplay with capacitative Ca²⁺ entry (CCE) and ER Ca²⁺ release and uptake. We have determined its contribution to the Ca²⁺ signal and how it varies with different physiological stimuli, including single and repeated carbachol applications and brief and prolonged exposures.

In agreement with previous work, carbachol stimulated a rise in intracellular Ca²⁺ in the endothelial cells, consisting of a rapid initial phase, then a plateau upon which oscillations of Ca²⁺ were superimposed, followed by a decline to basal Ca²⁺ levels upon carbachol removal. Our data support the following conclusions: (i) the size (amplitude and duration) of the Ca²⁺ spike and early oscillations are limited by SERCA activity, thus both are increased if SERCA is inhibited. (ii) SERCA activity is such that brief applications of carbachol do not trigger CCE, presumably because the fall in luminal Ca²⁺ is not sufficient to trigger it. However, longer applications sufficient to deplete the ER or even partial SERCA inhibition stimulate CCE. (iii) Ca²⁺ entry occurs via STIM-mediated CCE and SERCA contributes to the cessation of CCE. In conclusion our data show how SERCA function is crucial to shaping endothelial cell Ca signals and its dynamic interplay with both CCE and ER Ca releases.

TRP channels and their implications in metabolic diseases

The transient receptor potential (TRP) channel superfamily is composed of 28 nonselective cation channels that are ubiquitously expressed in many cell types and have considerable functional diversity. Although changes in TRP channel expression and function have been reported in cardiovascular disease and renal disorders, the pathogenic roles of TRP channels in metabolic diseases have not been systemically reviewed. In this review, we summarised the distribution of TRP channels in several metabolic tissues and discussed their roles in mediating and regulating various physiological and pathophysiological metabolic processes and diseases including diabetes, obesity, dyslipidaemia, metabolic syndrome, atherosclerosis, metabolic bone diseases and electrolyte disturbances. This review provides new insight into the involvement of TRP channels in the pathogenesis of metabolic disorders and implicates these channels as potential therapeutic targets for the management of metabolic diseases.

Klotho is associated with VEGF receptor-2 and the transient receptor potential canonical-1 Ca2+ channel to maintain endothelial integrity

Klotho is a circulating protein, and Klotho deficiency disturbs endothelial integrity, but the molecular mechanism is not fully clarified. We report that vascular endothelium in Klotho-deficient mice showed hyperpermeability with increased apoptosis and down-regulation of vascular endothelial (VE)-cadherin because of an increase in VEGF-mediated internal calcium concentration ([Ca(2+)]i) influx and hyperactivation of Ca(2+)-dependent proteases. Immunohistochemical analysis, the pull-down assay using Klotho-fixed agarose, and FRET confocal imaging confirmed that Klotho protein binds directly to VEGF receptor 2 (VEGFR-2) and endothelial, transient-receptor potential canonical Ca(2+) channel 1 (TRPC-1) and strengthens the association to promote their cointernalization. An in vitro mutagenesis study revealed that the second hydrolase domain of Klotho interacts with sixth and seventh Ig domains of VEGFR-2 and the third extracellular loop of TRPC-1. In Klotho-deficient endothelial cells, VEGF-mediated internalization of the VEGFR-2/TRPC-1 complex was impaired, and surface TRPC-1 expression increased 2.2-fold; these effects were reversed by supplementation of Klotho protein. VEGF-mediated elevation of [Ca(2+)]i was sustained at higher levels in an extracellular Ca(2+)-dependent manner, and normalization of TRCP-1 expression restored the abnormal [Ca(2+)]i handling. These findings provide evidence that Klotho protein is associated with VEGFR-2/TRPC-1 in causing cointernalization, thus regulating TRPC-1-mediated Ca(2+) entry to maintain endothelial integrity.

Multiple roles of protein kinase a in arachidonic acid-mediated Ca2+ entry and tumor-derived human endothelial cell migration

We recently showed that arachidonic acid (AA) triggers calcium signals in endothelial cells derived from human breast carcinoma (B-TEC). In particular, AA-dependent Ca(2+) entry is involved in the early steps of tumor angiogenesis in vitro. Here, we investigated the multiple roles of the nitric oxide (NO) and cyclic AMP/protein kinase A (PKA) pathways in AA-mediated Ca(2+) signaling in the same cells. B-TEC stimulation with 5 μmol/L AA resulted in endothelial NO synthase (NOS) phosphorylation at Ser(1177), and NO release was measured with the fluorescent NO-sensitive probe DAR4M-AM. PKA inhibition by the use of the membrane-permeable PKA inhibitory peptide myristoylated PKI(14-22) completely prevented both AA- and NO-induced calcium entry and abolished B-TEC migration promoted by AA. AA-dependent calcium entry and cell migration were significantly affected by both the NOS inhibitor N(G)-nitro-l-arginine methyl ester and the NO scavenger 2-phenyl-4,4,5,5-tetramethylimidazoline-1-oxyl 3-oxide, suggesting that NO release is functionally involved in the signaling dependent on AA. Moreover, pretreatment with carboxyamidotriazole, an antiangiogenic compound that interferes with agonist-activated calcium entry, prevented AA-dependent B-TEC motility. Interestingly, even in the absence of AA, enhancement of the cyclic AMP/PKA pathway with the adenylyl cyclase activator forskolin evoked a calcium entry dependent on NOS recruitment and NO release. The functional relevance of AA-induced calcium entry could be restricted to tumor-derived endothelial cells (EC) because AA evoked a smaller calcium entry in normal human microvascular ECs compared with B-TECs, and even more importantly, it was unable to promote cell motility in wound healing assay. This evidence opens an intriguing opportunity for differential pharmacologic treatment between normal and tumor-derived human ECs.

Activation of TRPV1 by dietary capsaicin improves endothelium-dependent vasorelaxation and prevents hypertension

Some plant-based diets lower the cardiometabolic risks and prevalence of hypertension. New evidence implies a role for the transient receptor potential vanilloid 1 (TRPV1) cation channel in the pathogenesis of cardiometabolic diseases. Little is known about impact of chronic TRPV1 activation on the regulation of vascular function and blood pressure. Here we report that chronic TRPV1 activation by dietary capsaicin increases the phosphorylation of protein kinase A (PKA) and eNOS and thus production of nitric oxide (NO) in endothelial cells, which is calcium dependent. TRPV1 activation by capsaicin enhances endothelium-dependent relaxation in wild-type mice, an effect absent in TRPV1-deficient mice. Long-term stimulation of TRPV1 can activate PKA, which contributes to increased eNOS phosphorylation, improves vasorelaxation, and lowers blood pressure in genetically hypertensive rats. We conclude that TRPV1 activation by dietary capsaicin improves endothelial function. TRPV1-mediated increase in NO production may represent a promising target for therapeutic intervention of hypertension.

Functional distinctions in cytosolic calcium regulation between cells of the glomerular filtration barrier

The importance of intracellular calcium ([Ca(2+)]i) regulation in the glomerular filtration barrier (GFB) has recently been highlighted by mutations in the cation channel TRPC6, resulting in a renal-specific phenotype. We examined the effects of FFA, a tool that can activate TRPC6, on [Ca(2+)]i in human conditionally immortalised glomerular endothelial cells (ciGEnC) and human podocytes (ciPod) that form the GFB. Changes in [Ca(2+)]i stimulated by FFA were measured in Fura 2-AM loaded cells. In GEnC, cell activation by FFA was dependent on external Ca(2+), yet in ciPod it was not. Depletion of internal Ca(2+) stores with thapsigargin did not affect cell activation by FFA in ciGEnC, but inhibited it in ciPod in a nephrin-dependent manner, demonstrated using nephrin deficient (ND) ciPod in conjunction with nephrin rescue experiments. FFA induced [Ca(2+)]i store release in ciPod, but not in ciGEnC or ND ciPod. In parallel, there were differences in the localisation of overexpressed TRPC6 between ciGEnC and ciPod. Furthermore, co-transfection of nephrin with TRPC6 in HEK293 cells reduced the FFA-induced increase in [Ca(2+)]i and nephrin clustering altered TRPC6 distribution. In conclusion, cell activation by FFA in podocytes stimulates the opening of a Ca(2+) channel, probably TRPC6, in a nephrin-dependent manner with a different activation profile to GEnC.

Polyunsaturated docosahexaenoic acid suppresses oxidative stress induced endothelial cell calcium influx by altering lipid composition in membrane caveolar rafts

OBJECTIVE

To determine whether DHA suppresses oxidative stress induced endothelial cell calcium influx by altering lipid composition and TRPC1 distribution in membrane rafts.

METHODS

Endothelial cells (EC) were pretreated with DHA or stearic acid, then incubated for another 3h with media containing H(2)O(2). Membrane lipid rafts were isolated using the discontinuous sucrose density gradient ultracentrifugation method. Intracellular calcium was detected with laser scanning confocal microscope. TRPC1 protein in membrane fractions was detected by immunoblotting. Membrane fatty acids compositions were analyzed by gas chromatography; raft cholesterol level was assayed by an Amplex Red Cholesterol Assay kit, and DAG concentration was quantified by a DAG kinase assay.

RESULTS

DHA significantly reduced oxidative stress induced calcium influx; pretreated with DHA the n-3 PUFAs were significantly increased in raft fractions, as well as saturated myristic acid, palmitic acid content of membrane rafts in EC; while the stearic acid, monounsaturated oleic acid and cis-oleic acid were decreased. Incubation with DHA also significantly reduced the amount of SM and cholesterol levels in the raft. Interestingly, we fractioned plasma membrane subcellular compartments and discovered that certain amounts of TRPC1 existed in detergent-resistant plasma membrane fractions of EC. After DHA treatment, TRPC1 was partly displaced from lipid raft to detergent-soluble membrane fractions.

CONCLUSIONS

DHA significantly reduces oxidative stress induced endothelial calcium influx, this effect might be associated with, at least in part, altered raft lipid environment, and suppresses TRPC1-mediated calcium signaling pathway by partially displacing TRPC1 from membrane caveolar lipid rafts.

Cyclic nucleotide-gated channels: a familiar channel family with a new function?

The cyclic nucleotide-gated (CNG) channel is a family of nonselective cation channels that open in response to an elevated cyclic nucleotide level. Cyclic nucleotides, particularly cAMP and cGMP, govern a great diversity of cellular functions. While the pivotal roles of CNG channels in the visual and olfactory systems have been well established in the past decade, relatively few studies were performed regarding the functional roles of CNG channels in non-neuronal systems. Cyclic nucleotides and Ca2+ are key signaling molecules in cardiovascular systems. Given that CNG channels are expressed in vascular tissues, several recent studies have explored the possible functional role of CNG channels in cardiovascular systems. This article intends to summarize some recent developments regarding the expression and functional role of CNG channels in the cardiovascular system.

Temperature sensitivity of suicidal erythrocyte death

BACKGROUND

Fever and hyperthermia are frequently associated with anaemia. Under most clinical conditions, they are considered to be two mutually independent clinical consequences of a common cause. The present study explored the possibility that anaemia results from temperature-sensitive suicidal erythrocyte death or eryptosis. Eryptosis is characterised by cell shrinkage and cell membrane scrambling with phosphatidylserine (PS) exposure at the erythrocyte surface. It is triggered by increase in the cytosolic Ca(2+) activity on the one hand and by ceramide formation on the other.

MATERIAL AND METHODS

Annexin V-binding was utilised to disclose PS exposure, forward scatter to analyse cell volume, Fluo 3 fluorescence to estimate cytosolic Ca(2+) activity, binding of fluorescent antibodies to determine ceramide abundance and a luciferin/luciferase-based assay to measure the cytosolic ATP concentration.

RESULTS

Graded increases in temperature from 37 to 41 degrees C decreased the forward scatter and stimulated annexin V-binding of human erythrocytes. The effect was accompanied by increased cytosolic Ca(2+) activity, decrease of the cellular ATP content and a moderate rise in ceramide formation. The effect of hyperthermia on annexin V-binding was significantly blunted by the leukotriene receptor CysLT1 antagonist cinalukast (1 microM).

CONCLUSIONS

Hyperthermia stimulates Ca(2+) entry into erythrocytes leading to cell shrinkage and PS exposure. As PS-exposing erythrocytes are rapidly cleared from circulating blood, the eryptosis during hyperthermia may cause anaemia.

The Constitutive Function of Native TRPC3 Channels Modulates Vascular Cell Adhesion Molecule-1 Expression in Coronary Endothelial Cells Through Nuclear Factor κB Signaling

Rationale : Upregulation of endothelial vascular cell adhesion molecule (VCAM)-1 and the subsequent increase in monocyte recruitment constitute critical events in atherogenesis. We have recently shown that in human coronary artery endothelial cells (HCAECs) regulated expression of VCAM-1 depends, to a significant extent, on expression and function of the Ca 2+ -permeable channel transient receptor potential canonical (TRPC)3, regardless of the ability of the stimulatory signal to induce regulated Ca 2+ influx, leading to the hypothesis that TRPC3 constitutive, rather than regulated function, contributes to the underlying signaling mechanism.

Objective : The present studies addressed this important question and gathered mechanistic insight on the signaling coupling constitutive TRPC3 function to VCAM-1 expression.

Methods and Results : In HCAECs, maneuvers that prevent Ca 2+ influx or knockdown of TRPC3 markedly reduced tumor necrosis factor (TNF)α-induced VCAM-1 and monocyte adhesion. TNFα also induced TRPC3 expression and TRPC3-mediated constitutive cation influx and currents. Stable (HEK293 cells) or transient (HCAECs) overexpression of TRPC3 enhanced TNFα-induced VCAM-1 compared to wild-type cells. IκBα phosphorylation/degradation was reduced by TRPC3 knockdown and increased by channel overexpression. Inhibition of calmodulin completely prevented nuclear factor κB activation, whereas blocking calmodulin-dependent kinases or NADPH oxidases rendered partial inhibition.

Conclusions : Our findings indicate that in HCAECs expression of VCAM-1 and monocyte adhesion depend, to a significant extent, on TRPC3 constitutive function through a signaling mechanism that requires constitutive TRPC3-mediated Ca 2+ influx for proper activation of nuclear factor κB, presumably through Ca 2+ -dependent activation of the calmodulin/calmodulin-dependent kinase axis.

Electrophysiological characterization of store-operated and agonist-induced Ca2+ entry pathways in endothelial cells

In endothelial cells, agonist-induced Ca(2+) entry takes place via the store-operated Ca(2+) entry pathway and/or via channel(s) gated by second messengers. As cell stimulation leads to both a partial Ca(2+) store depletion as well as the production of second messengers, these two pathways are problematic to distinguish. We showed that passive endoplasmic reticulum (ER) depletion by thapsigargin or cell stimulation by histamine activated a similar Ca(2+)-release-activated Ca(2+) current (CRAC)-like current when 10 mM Ba(2+)/2 mM Ca(2+) was present in the extracellular solution. Importantly, during voltage clamp recordings, histamine stimulation largely depleted the ER Ca(2+) store, explaining the activation of a CRAC-like current (due to store depletion) upon histamine in Ba(2+) medium. On the contrary, in the presence of 10 mM Ca(2+), the ER Ca(2+) content remained elevated, and histamine induced an outward rectifying current that was inhibited by Ni(2+) and KB-R7943, two blockers of the Na(+)/Ca(2+) exchanger (NCX). Both blockers also reduced histamine-induced cytosolic Ca(2+) elevation. In addition, removing extracellular Na(+) increased the current amplitude which is in line with a current supported by the NCX. These data are consistent with the involvement of the NCX working in reverse mode (Na(+) out/Ca(2+) in) during agonist-induced Ca(2+) entry in endothelial cells.

Endothelium-derived hyperpolarising factors and associated pathways: a synopsis

The term endothelium-derived hyperpolarising factor (EDHF) was introduced in 1987 to describe the hypothetical factor responsible for myocyte hyperpolarisations not associated with nitric oxide (EDRF) or prostacyclin. Two broad categories of EDHF response exist. The classical EDHF pathway is blocked by apamin plus TRAM-34 but not by apamin plus iberiotoxin and is associated with endothelial cell hyperpolarisation. This follows an increase in intracellular [Ca(2+)] and the opening of endothelial SK(Ca) and IK(Ca) channels preferentially located in caveolae and in endothelial cell projections through the internal elastic lamina, respectively. In some vessels, endothelial hyperpolarisations are transmitted to myocytes through myoendothelial gap junctions without involving any EDHF. In others, the K(+) that effluxes through SK(Ca) activates myocytic and endothelial Ba(2+)-sensitive K(IR) channels leading to myocyte hyperpolarisation. K(+) effluxing through IK(Ca) activates ouabain-sensitive Na(+)/K(+)-ATPases generating further myocyte hyperpolarisation. For the classical pathway, the hyperpolarising "factor" involved is the K(+) that effluxes through endothelial K(Ca) channels. During vessel contraction, K(+) efflux through activated myocyte BK(Ca) channels generates intravascular K(+) clouds. These compromise activation of Na(+)/K(+)-ATPases and K(IR) channels by endothelium-derived K(+) and increase the importance of gap junctional electrical coupling in myocyte hyperpolarisations. The second category of EDHF pathway does not require endothelial hyperpolarisation. It involves the endothelial release of factors that include NO, HNO, H(2)O(2) and vasoactive peptides as well as prostacyclin and epoxyeicosatrienoic acids. These hyperpolarise myocytes by opening various populations of myocyte potassium channels, but predominantly BK(Ca) and/or K(ATP), which are sensitive to blockade by iberiotoxin or glibenclamide, respectively.

Oxidant sensing by protein kinases a and g enables integration of cell redox state with phosphoregulation

The control of vascular smooth muscle contractility enables regulation of blood pressure, which is paramount in physiological adaptation to environmental challenges. Maintenance of stable blood pressure is crucial for health as deregulation (caused by high or low blood pressure) leads to disease progression. Vasotone is principally controlled by the cyclic nucleotide dependent protein kinases A and G, which regulate intracellular calcium and contractile protein calcium sensitivity. The classical pathways for activation of these two kinases are well established and involve the formation and activation by specific cyclic nucleotide second messengers. Recently we reported that both PKA and PKG can be regulated independently of their respective cyclic nucleotides via a mechanism whereby the kinases sense cellular oxidant production using redox active thiols. This novel redox regulation of these kinases is potentially of physiological importance, and may synergise with the classical regulatory mechanisms.

Epoxyeicosatrienoic acids and endothelium-dependent responses

Epoxyeicosatrienoic acids (EETs) are cytochrome P450 metabolites of arachidonic acid that are produced by the vascular endothelium in response to agonists such as bradykinin and acetylcholine or physical stimuli such as shear stress or cyclic stretch. In the vasculature, the EETs have biological actions that are involved in the regulation of vascular tone, hemostasis, and inflammation. In preconstricted arteries in vitro, EETs activate calcium-activated potassium channels on vascular smooth muscle and the endothelium causing membrane hyperpolarization and relaxation. These effects are observed in a variety of arteries from experimental animals and humans; however, this is not a universal finding in all arteries. The mechanism of EET action may vary. In some arteries, EETs are released from the endothelium and are transferred to the smooth muscle where they cause potassium channel activation, hyperpolarization, and relaxation through a guanine nucleotide binding protein-coupled mechanism or transient receptor potential (TRP) channel activation. In other arteries, EETs activate TRP channels on the endothelium to cause endothelial hyperpolarization that is transferred to the smooth muscle by gap junctions or potassium ion. Some arteries use a combination of mechanisms. Acetylcholine and bradykinin increase blood flow in dogs and humans that is inhibited by potassium channel blockers and cytochrome P450 inhibitors. Thus, the EETs are endothelium-derived hyperpolarizing factors mediating a portion of the relaxations to acetylcholine, bradykinin, shear stress, and cyclic stretch and regulate vascular tone in vitro and in vivo.

Pharmacology of transient receptor potential melastatin channels in the vasculature

Mammalian transient receptor potential melastatin (TRPM) non-selective cation channels, the largest TRP subfamily, are widely expressed in excitable and non-excitable cells where they perform diverse functions ranging from detection of cold, taste, osmolarity, redox state and pH to control of Mg(2+) homeostasis and cell proliferation or death. Recently, TRPM gene expression has been identified in vascular smooth muscles with dominance of the TRPM8 channel. There has been in parallel considerable progress in decoding the functional roles of several TRPMs in the vasculature. This research on native cells is aided by the knowledge of the activation mechanisms and pharmacological properties of heterologously expressed TRPM subtypes. This paper summarizes the present state of knowledge of vascular TRPM channels and outlines several anticipated directions of future research in this area.

Genistein potentiates activity of the cation channel TRPC5 independently of tyrosine kinases

BACKGROUND AND PURPOSE

TRPC5 is a Ca(2+)-permeable channel with multiple modes of activation. We have explored the effects of genistein, a plant-derived isoflavone, on TRPC5 activity, and the mechanism(s) involved.

EXPERIMENTAL APPROACH

Effects of genistein on TRPC5 channels were investigated in TRPC5-over-expressing human embryonic kidney 293 (HEK) cells and bovine aortic endothelial cells (BAECs) using fluorescent Ca(2+) imaging and electrophysiological techniques.

KEY RESULTS

In TRPC5-over-expressing HEK cells, genistein stimulated TRPC5-mediated Ca(2+) influx, concentration dependently (EC(50)= 93 microM). Genistein and lanthanum activated TRPC5 channels synergistically. Effects of genistein on TRPC5 channels were mimicked by daidzein (100 microM), a genistein analogue inactive as a tyrosine kinase inhibitor, but not by known tyrosine kinase inhibitors herbimycin (2 microM), PP2 (20 microM) and lavendustin A (10 microM). Action of genistein on TRPC5 channels was not affected by an oestrogen receptor inhibitor ICI-182780 (50 microM) or a phospholipase C inhibitor U73122 (10 microM), suggesting genistein did not act through oestrogen receptors or phospholipase C. In BAECs, genistein (100 microM) stimulated TRPC5-mediated Ca(2+) influx. In patch clamp studies, both genistein (50 microM) and daidzein (50 microM) augmented TRPC5-mediated whole-cell cation current in TRPC5 over-expressing HEK cells. Genistein stimulated TRPC5 channel activity in excised inside-out membrane patch, suggesting that its action was relatively direct and did not require cytosolic factors.

CONCLUSIONS AND IMPLICATIONS

The present study is the first to demonstrate stimulation of a TRP channel by isoflavones. Genistein is a lipophilic compound able to stimulate TRPC5 activity in TRPC5-over-expressing HEK cells and in native vascular endothelial cells.

TRPC1 is essential for in vivo angiogenesis in zebrafish

RATIONALE

Wiring vascular and neural networks are known to share common molecular signaling pathways. Activation of transient receptor potential type C channels (TRPCs) has recently been shown to underlie chemotropic guidance of neural axons. It is thus of interest to examine whether TRPCs are also involved in vascular development.

OBJECTIVE

To determine the role of TRPC1 in angiogenesis in vivo during zebrafish development.

METHODS AND RESULTS

Knockdown of zebrafish trpc1 by antisense morpholino oligonucleotides severely disrupted angiogenic sprouting of intersegmental vessels (ISVs) in zebrafish larvae. This angiogenic defect was prevented by overexpression of a morpholino oligonucleotide-resistant form of zebrafish trpc1 mRNA. Cell transplantation analysis showed that this requirement of Trpc1 for ISV growth was endothelial cell-autonomous. In vivo time-lapse imaging further revealed that the angiogenic defect was attributable to impairment of filopodia extension, migration, and proliferation of ISV tip cells. Furthermore, Trpc1 acted synergistically with vascular endothelial growth factor A (Vegf-a) in controlling ISV growth, and appeared to be downstream to Vegf-a in controlling angiogenesis, as evidence by the findings that Trpc1 was required for Vegf-a-induced ectopic angiogenesis of subintestinal veins and phosphorylation of extracellular signal-regulated kinase.

CONCLUSIONS

These results provide the first in vivo evidence that TRPC1 is essential for angiogenesis, reminiscent of the role of TRPCs in axon guidance. It implicates that TRPC1 may represent a potential target for treating pathological angiogenesis.

Phosphorylation of TRPC6 channels at Thr69 is required for anti-hypertrophic effects of phosphodiesterase 5 inhibition

Activation of Ca(2+) signaling induced by receptor stimulation and mechanical stress plays a critical role in the development of cardiac hypertrophy. A canonical transient receptor potential protein subfamily member, TRPC6, which is activated by diacylglycerol and mechanical stretch, works as an upstream regulator of the Ca(2+) signaling pathway. Although activation of protein kinase G (PKG) inhibits TRPC6 channel activity and cardiac hypertrophy, respectively, it is unclear whether PKG suppresses cardiac hypertrophy through inhibition of TRPC6. Here, we show that inhibition of cGMP-selective PDE5 (phosphodiesterase 5) suppresses endothelin-1-, diacylglycerol analog-, and mechanical stretch-induced hypertrophy through inhibition of Ca(2+) influx in rat neonatal cardiomyocytes. Inhibition of PDE5 suppressed the increase in frequency of Ca(2+) spikes induced by agonists or mechanical stretch. However, PDE5 inhibition did not suppress the hypertrophic responses induced by high KCl or the activation of protein kinase C, suggesting that PDE5 inhibition suppresses Ca(2+) influx itself or molecule(s) upstream of Ca(2+) influx. PKG activated by PDE5 inhibition phosphorylated TRPC6 proteins at Thr(69) and prevented TRPC6-mediated Ca(2+) influx. Substitution of Ala for Thr(69) in TRPC6 abolished the anti-hypertrophic effects of PDE5 inhibition. In addition, chronic PDE5 inhibition by oral sildenafil treatment actually induced TRPC6 phosphorylation in mouse hearts. Knockdown of RGS2 (regulator of G protein signaling 2) and RGS4, both of which are activated by PKG to reduce G alpha(q)-mediated signaling, did not affect the suppression of receptor-activated Ca(2+) influx by PDE5 inhibition. These results suggest that phosphorylation and functional suppression of TRPC6 underlie prevention of pathological hypertrophy by PDE5 inhibition.

Transient receptor potential channelopathies

In the past years, several hereditary diseases caused by defects in transient receptor potential channels (TRP) genes have been described. This review summarizes our current knowledge about TRP channelopathies and their possible pathomechanisms. Based on available genetic indications, we will also describe several putative pathological conditions in which (mal)function of TRP channels could be anticipated.