Depletion of intracellular Ca2+ stores enhances flow-induced vascular dilatation in rat small mesenteric artery

Irisin Regulates Cardiac Responses to Exercise in Health and Diseases: a Narrative Review

Exercise has been recognized as an important non-pharmacological approach for the prevention, treatment, and rehabilitation of cardiovascular diseases, but the mechanisms of exercise in promoting cardiovascular health remain unclear. Exercise generates cardiac benefits via stimulating muscle to secret hundreds of myokines that directly enter circulation and target heart tissue. Therefore, inter-organ communication between skeletal muscle and heart may be one important regulating pattern, and such communication can occur through secretion of molecules, frequently known as myokines. Irisin, a newly identified myokine, is cleaved from fibronectin type III domain-containing protein 5 (FNDC5) and secreted by the stimulation of exercise. Recently, accumulating evidence focusing on the interaction between irisin and cardiac function has been reported. This review highlights the molecular signaling by which irisin regulates the benefits of exercise on cardiac function both in physiological and pathological process, and discusses the clinical potential of irisin in treating heart diseases. Exercise generates various cardiovascular benefits through stimulating skeletal muscle to secrete irisin. The exercise "hormone" irisin, both produced by exercise or recombinant form, exerts therapeutic effects in a group of cardiovascular disorders including heart failure, myocardial infarction, atherosclerosis and hypertension. However, the molecular mechanisms involved remain ambiguous.This review highlights the most up-to-date findings to bridge the gap between exercise, irisin and cardiovascular diseases, and discusses the potential clinical prospect of irisin.

High Salt Upregulates Ca2+-Sensing Receptor Expression and Ca2+-Induced Relaxation of Contracted Mesenteric Arteries from Dahl Salt-Sensitive Rats

High Ca2+ lowers blood pressure in hypertension, but the mechanism is not clear. The missing link may be the perivascular sensory nerve Ca2+-sensing receptor (CaSR) that mediates a vasodilator system after activation by interstitial Ca2+ Our results show that high salt increased CaSR expression in mesenteric arteries as well as Ca2+ relaxation of contracted mesenteric arteries from salt-sensitive (SS) rats. The CaSR was expressed as a doublet (≈120-150 kDa) in arteries from animals fed a high-salt diet for 1-4 weeks. The higher molecular weight glycosylated protein increased in arteries from SS animals; however, expression of the low molecular mass high-mannose protein decreased over 4 weeks of feeding the diet. In tissues from salt-resistant (SR) rats, the diet decreased CaSR expression after 4 weeks. Ca2+ relaxation of mesenteric arteries under phenylephrine tone increased in SS rats but decreased in arteries from SR rats fed the high-salt diet. Ca2+-activated K+ channels have a larger role in Ca2+ relaxation of arteries in SR than SS rats. The data suggest that high salt epigenetically regulates the receptor at the translational level in vivo and that the in vitro effect of Ca2+ is on receptor trafficking and signaling. In conclusion, upregulated expression of the CaSR in salt sensitivity increased receptor-mediated vascular relaxation. These findings show that CaSR signaling may compensate for changes in the vasculature in salt-sensitive hypertension. SIGNIFICANCE STATEMENT: The perivascular sensory nerve Ca2+-sensing receptor (CaSR) mediates Ca2+ relaxation of isolated mesenteric arteries under tension. This receptor may therefore play a significant role in relaxation of resistance arteries in vivo, thus explaining the blood pressure-lowering effect of dietary Ca2+. The present studies describe the effect of high salt-induced upregulation of the CaSR in salt-sensitive rats and the roles played by Ca2+-activated K+ channels and nitric oxide in Ca2+ responses.

Protein kinase N2 mediates flow-induced endothelial NOS activation and vascular tone regulation

Formation of NO by endothelial NOS (eNOS) is a central process in the homeostatic regulation of vascular functions including blood pressure regulation, and fluid shear stress exerted by the flowing blood is a main stimulus of eNOS activity. Previous work has identified several mechanosensing and -transducing processes in endothelial cells, which mediate this process and induce the stimulation of eNOS activity through phosphorylation of the enzyme via various kinases including AKT. How the initial mechanosensing and signaling processes are linked to eNOS phosphorylation is unclear. In human endothelial cells, we demonstrated that protein kinase N2 (PKN2), which is activated by flow through the mechanosensitive cation channel Piezo1 and Gq/G11-mediated signaling, as well as by Ca2+ and phosphoinositide-dependent protein kinase 1 (PDK1), plays a pivotal role in this process. Active PKN2 promoted the phosphorylation of human eNOS at serine 1177 and at a newly identified site, serine 1179. These phosphorylation events additively led to increased eNOS activity. PKN2-mediated eNOS phosphorylation at serine 1177 involved the phosphorylation of AKT synergistically with mTORC2-mediated AKT phosphorylation, whereas active PKN2 directly phosphorylated human eNOS at serine 1179. Mice with induced endothelium-specific deficiency of PKN2 showed strongly reduced flow-induced vasodilation and developed arterial hypertension accompanied by reduced eNOS activation. These results uncover a central mechanism that couples upstream mechanosignaling processes in endothelial cells to the regulation of eNOS-mediated NO formation, vascular tone, and blood pressure.

NADPH oxidase in the vasculature: Expression, regulation and signalling pathways; role in normal cardiovascular physiology and its dysregulation in hypertension

The last 20-25 years have seen an explosion of interest in the role of NADPH oxidase (NOX) in cardiovascular function and disease. In vascular smooth muscle and endothelium, NOX generates reactive oxygen species (ROS) that act as second messengers, contributing to the control of normal vascular function. NOX activity is altered in response to a variety of stimuli, including G-protein coupled receptor agonists, growth-factors, perfusion pressure, flow and hypoxia. NOX-derived ROS are involved in smooth muscle constriction, endothelium-dependent relaxation and smooth muscle growth, proliferation and migration, thus contributing to the fine-tuning of blood flow, arterial wall thickness and vascular resistance. Through reversible oxidative modification of target proteins, ROS regulate the activity of protein tyrosine phosphatases, kinases, G proteins, ion channels, cytoskeletal proteins and transcription factors. There is now considerable, but somewhat contradictory evidence that NOX contributes to the pathogenesis of hypertension through oxidative stress. Specific NOX isoforms have been implicated in endothelial dysfunction, hyper-contractility and vascular remodelling in various animal models of hypertension, pulmonary hypertension and pulmonary arterial hypertension, but also have potential protective effects, particularly NOX4. This review explores the multiplicity of NOX function in the healthy vasculature and the evidence for and against targeting NOX for antihypertensive therapy.

Royal jelly increases peripheral circulation by inducing vasorelaxation through nitric oxide production under healthy conditions

AIMS

Royal jelly (RJ) has a variety of reported biological activities, including vasorelaxation and blood pressure-lowering effects. Although functional foods are positively used for health, the effects of RJ on the cardiovascular system in healthy individuals have not been well studied. Therefore, we investigated the mechanisms underlying the vasorelaxation effects of RJ in healthy control rats to evaluate whether the peripheral circulation was increased.

MAIN METHODS

We used fresh RJ to examine the vasorelaxation effects and related mechanisms in Wistar rats using organ bath techniques. Furthermore, we measured changes in tail blood circulation, systolic blood pressure (sBP), and heart rate (HR) after the oral administration of RJ to control rats and nitro-l-arginine methyl ester (l-NAME)-treated rats (0.5 mg/ml dissolved in distilled drinking water for 1 week). Concentrations of acetylcholine (ACh) in the RJ were measured using a commercial kit.

KEY FINDINGS

RJ caused vasorelaxation of isolated rat aortas and superior mesenteric arteries, and this effect was inhibited by atropine (10^-5 M, 15 min) or L-NAME (10^-4 M, 20 min) and endothelium-denuded arterial ring preparations. Oral RJ increased tail blood flow and mass in control rats 1 h after treatment without affecting velocity, sBP, or HR. These effects were not observed in L-NAME-treated rats. RJ contained approximately 1000 μg/g of ACh.

SIGNIFICANCE

The present study demonstrated that RJ is composed of muscarinic receptor agonist(s), likely ACh, and induces vasorelaxation through nitric oxide (NO) production from the vascular endothelium of healthy rats, leading to increased tail blood circulation. Thus, fresh RJ may improve peripheral circulation in healthy individuals.

Acetylcholine released by endothelial cells facilitates flow-mediated dilatation

KEY POINTS

The endothelium plays a pivotal role in the vascular response to chemical and mechanical stimuli. The endothelium is exquisitely sensitive to ACh, although the physiological significance of ACh-induced activation of the endothelium is unknown. In the present study, we investigated the mechanisms of flow-mediated endothelial calcium signalling. Our data establish that flow-mediated endothelial calcium responses arise from the autocrine action of non-neuronal ACh released by the endothelium.

ABSTRACT

Circulating blood generates frictional forces (shear stress) on the walls of blood vessels. These frictional forces critically regulate vascular function. The endothelium senses these frictional forces and, in response, releases various vasodilators that relax smooth muscle cells in a process termed flow-mediated dilatation. Although some elements of the signalling mechanisms have been identified, precisely how flow is sensed and transduced to cause the release of relaxing factors is poorly understood. By imaging signalling in large areas of the endothelium of intact arteries, we show that the endothelium responds to flow by releasing ACh. Once liberated, ACh acts to trigger calcium release from the internal store in endothelial cells, nitric oxide production and artery relaxation. Flow-activated release of ACh from the endothelium is non-vesicular and occurs via organic cation transporters. ACh is generated following mitochondrial production of acetylCoA. Thus, we show ACh is an autocrine signalling molecule released from endothelial cells, and identify a new role for the classical neurotransmitter in endothelial mechanotransduction.

Endothelial cation channel PIEZO1 controls blood pressure by mediating flow-induced ATP release

Arterial blood pressure is controlled by vasodilatory factors such as nitric oxide (NO) that are released from the endothelium under the influence of fluid shear stress exerted by flowing blood. Flow-induced endothelial release of ATP and subsequent activation of Gq/G11-coupled purinergic P2Y2 receptors have been shown to mediate fluid shear stress-induced stimulation of NO formation. However, the mechanism by which fluid shear stress initiates these processes is unclear. Here, we have shown that the endothelial mechanosensitive cation channel PIEZO1 is required for flow-induced ATP release and subsequent P2Y2/Gq/G11-mediated activation of downstream signaling that results in phosphorylation and activation of AKT and endothelial NOS. We also demonstrated that PIEZO1-dependent ATP release is mediated in part by pannexin channels. The PIEZO1 activator Yoda1 mimicked the effect of fluid shear stress on endothelial cells and induced vasorelaxation in a PIEZO1-dependent manner. Furthermore, mice with induced endothelium-specific PIEZO1 deficiency lost the ability to induce NO formation and vasodilation in response to flow and consequently developed hypertension. Together, our data demonstrate that PIEZO1 is required for the regulation of NO formation, vascular tone, and blood pressure.

Essential Role of Smooth Muscle STIM1 in Hypertension and Cardiovascular Dysfunction

OBJECTIVES

Chronic hypertension is the most critical risk factor for cardiovascular disease, heart failure, and stroke.

APPROACH AND RESULTS

Here we show that wild-type mice infused with angiotensin II develop hypertension, cardiac hypertrophy, perivascular fibrosis, and endothelial dysfunction with enhanced stromal interaction molecule 1 (STIM1) expression in heart and vessels. All these pathologies were significantly blunted in mice lacking STIM1 specifically in smooth muscle (Stim1(SMC-/-)). Mechanistically, STIM1 upregulation during angiotensin II-induced hypertension was associated with enhanced endoplasmic reticulum stress, and smooth muscle STIM1 was required for endoplasmic reticulum stress-induced vascular dysfunction through transforming growth factor-β and nicotinamide adenine dinucleotide phosphate oxidase-dependent pathways. Accordingly, knockout mice for the endoplasmic reticulum stress proapoptotic transcriptional factor, CCAAT-enhancer-binding protein homologous protein (CHOP(-/-)), were resistant to hypertension-induced cardiovascular pathologies. Wild-type mice infused with angiotensin II, but not Stim1(SMC-/-) or CHOP(-/-) mice showed elevated vascular nicotinamide adenine dinucleotide phosphate oxidase activity and reduced phosphorylated endothelial nitric oxide synthase, cGMP, and nitrite levels.

CONCLUSIONS

Thus, smooth muscle STIM1 plays a crucial role in the development of hypertension and associated cardiovascular pathologies and represents a promising target for cardiovascular therapy.

Increasing TRPV4 expression restores flow-induced dilation impaired in mesenteric arteries with aging

The flow-stimulated intracellular Ca²⁺ concentration ([Ca²⁺]_i) rise in endothelial cells is an important early event leading to flow-induced blood vessel dilation. Transient receptor potential vanilloid subtype 4 (TRPV4), a Ca²⁺-permeable cation channel, facilitates the flow-stimulated [Ca²⁺]_i rise. To determine whether TRPV4 is involved in age-related flow-induced blood vessel dilation impairment, we measured blood vessel diameter and nitric oxide (NO) levels and performed Ca²⁺ imaging, immunoblotting, and immunostaining assays in rats. We found that the flow-induced and TRPV4 activator 4α-PDD-induced dilation of mesenteric arteries from aged rats were significantly decreased compared with those from young rats. The flow- or 4α-PDD-induced [Ca²⁺]_i rise was also markedly reduced in primary cultured mesenteric artery endothelial cells (MAECs) from aged rats. Immunoblotting and immunostaining results showed an age-related decrease of TRPV4 expression levels in MAECs. Additionally, the 4α-PDD-induced NO production was significantly reduced in aged MAECs. Compared with lentiviral GFP-treated aged rats, lentiviral vector delivery of TRPV4 increased TRPV4 expression level in aged MAECs and restored the flow- and 4α-PDD-induced vessel dilation in aged mesenteric arteries. We concluded that impaired TRPV4-mediated Ca²⁺ signaling causes endothelial dysfunction and that TRPV4 is a potential target for clinical treatment of age-related vascular system diseases.

P2Y₂ and Gq/G₁₁ control blood pressure by mediating endothelial mechanotransduction

Elevated blood pressure is a key risk factor for developing cardiovascular diseases. Blood pressure is largely determined by vasodilatory mediators, such as nitric oxide (NO), that are released from the endothelium in response to fluid shear stress exerted by the flowing blood. Previous work has identified several mechanotransduction signaling processes that are involved in fluid shear stress-induced endothelial effects, but how fluid shear stress initiates the response is poorly understood. Here, we evaluated human and bovine endothelial cells and found that the purinergic receptor P2Y2 and the G proteins Gq/G11 mediate fluid shear stress-induced endothelial responses, including [Ca2+]i transients, activation of the endothelial NO synthase (eNOS), phosphorylation of PECAM-1 and VEGFR-2, as well as activation of SRC and AKT. In response to fluid shear stress, endothelial cells released ATP, which activates the purinergic P2Y2 receptor. Mice with induced endothelium-specific P2Y2 or Gq/G11 deficiency lacked flow-induced vasodilation and developed hypertension that was accompanied by reduced eNOS activation. Together, our data identify P2Y2 and Gq/G11 as a critical endothelial mechanosignaling pathway that is upstream of previously described mechanotransduction processes and demonstrate that P2Y2 and Gq/G11 are required for basal endothelial NO formation, vascular tone, and blood pressure.

Vascular TRP channels: performing under pressure and going with the flow

Endothelial cells and smooth muscle cells of resistance arteries mediate opposing responses to mechanical forces acting on the vasculature, promoting dilation in response to flow and constriction in response to pressure, respectively. In this review, we explore the role of TRP channels, particularly endothelial TRPV4 and smooth muscle TRPC6 and TRPM4 channels, in vascular mechanosensing circuits, placing their putative mechanosensitivity in context with other proposed upstream and downstream signaling pathways.

Nicorandil directly and cyclic GMP-dependently opens K+ channels in human bypass grafts

As we previously demonstrated the role of different K(+) channels in the action of nicorandil on human saphenous vein (HSV) and human internal mammary artery (HIMA), this study aimed to analyse the contribution of the cGMP pathway in nicorandil-induced vasorelaxation and to determine the involvement of cGMP in the K(+) channel-activating effect of nicorandil. An inhibitor of soluble guanylate cyclase (GC), ODQ, significantly inhibited nicorandil-induced relaxation, while ODQ plus glibenclamide, a selective ATP-sensitive K(+) (KATP) channel inhibitor, produced a further inhibition of both vessels. In HSV, ODQ in combination with 4-aminopyridine, a blocker of voltage-gated K(+) (KV) channels, did not modify the concentration-response to nicorandil compared with ODQ, whereas in HIMA, ODQ plus iberiotoxin, a selective blocker of large-conductance Ca(2+)-activated K(+) (BKCa) channels, produced greater inhibition than ODQ alone. We showed that the cGMP pathway plays a significant role in the vasorelaxant effect of nicorandil on HSV and HIMA. It seems that nicorandil directly opens KATP channels in both vessels and BKCa channels in HIMA, although it is possible that stimulation of GC contributes to KATP channels activation in HIMA. Contrary, the activation of KV channels in HSV is probably due to GC activation and increased levels of cGMP.

Ageing alters perivascular nerve function of mouse mesenteric arteries in vivo

Abstract  Mesenteric arteries (MAs) are studied widely in vitro but little is known of their reactivity in vivo. Transgenic animals have enabled Ca(2+) signalling to be studied in isolated MAs but the reactivity of these vessels in vivo is undefined. We tested the hypothesis that ageing alters MA reactivity to perivascular nerve stimulation (PNS) and adrenoreceptor (AR) activation during blood flow control. First- (1A), second- (2A) and third-order (3A) MAs of pentobarbital-anaesthetized Young (3-6 months) and Old (24-26 months) male and female Cx40(BAC)-GCaMP2 transgenic mice (C57BL/6 background; positive or negative for the GCaMP2 transgene) were studied with intravital microscopy. A segment of jejunum was exteriorized and an MA network was superfused with physiological salt solution (pH 7.4, 37°C). Resting tone was 10% in MAs of Young and Old mice; diameters were ∼5% (1A), 20% (2A) and 40% (3A) smaller (P 0.05) in Old mice. Throughout MA networks, vasoconstriction increased with PNS frequency (1-16 Hz) but was ∼20% less in Young vs. Old mice (P 0.05) and was inhibited by tetrodotoxin (1 μm). Capsaicin (10 μm; to inhibit sensory nerves) enhanced MA constriction to PNS (P 0.05) by ∼20% in Young but not Old mice. Phenylephrine (an α1AR agonist) potency was greater in Young mice (P 0.05) with similar efficacy (∼60% constriction) across ages and MA branches. Constrictions to UK14304 (an α2AR agonist) were less (∼20%; P 0.05) and were unaffected by ageing. Irrespective of sex or transgene expression, ageing consistently reduced the sensitivity of MAs to α1AR vasoconstriction while blunting the attenuation of sympathetic vasoconstriction by sensory nerves. These findings imply substantive alterations in splanchnic blood flow control with ageing.

Apigenin, a plant-derived flavone, activates transient receptor potential vanilloid 4 cation channel

BACKGROUND AND PURPOSE

Transient receptor potential vanilloid 4 (TRPV4) is a Ca(2+) -permeable channel with multiple modes of activation. Apigenin is a plant-derived flavone, which has potential preventive effects on the development of cardiovascular disease. We set out to explore the effects of apigenin on TRPV4 channel activity and its role in vasodilatation.

EXPERIMENTAL APPROACH

The effects of apigenin (0.01-30 µM) on TPRV4 channels were investigated in HEK293 cells over-expressing TRPV4, rat primary cultured mesenteric artery endothelial cells (MAECs) and isolated small mesenteric arterial segments using whole-cell patch clamp, fluorescent Ca(2+) imaging, intracellular recording and pressure myography.

KEY RESULTS

Whole-cell patch clamp and fluorescent Ca(2+) imaging in HEK cells over-expressing TRPV4 showed that apigenin concentration-dependently stimulated the TRPV4-mediated cation current and Ca(2+) influx. In MAECs, apigenin stimulated Ca(2+) influx in a concentration-dependent manner. These increases in cation current and Ca(2+) influx were markedly inhibited by TRPV4-specific blockers and siRNAs. Furthermore, pressure myography and intracellular recording in small third-order mesenteric arteries showed that apigenin dose-dependently evoked smooth muscle cell membrane hyperpolarization and subsequent vascular dilatation, which were significantly inhibited by TRPV4-specific blockers. TRPV4 blocker or charybdotoxin (200 nM) plus apamin (100 nM) diminished the apigenin-induced dilatation.

CONCLUSION AND IMPLICATIONS

This is the first study to demonstrate the selective stimulation of TRPV4 by apigenin. Apigenin was found to activate TRPV4 channels in a dose-dependent manner in HEK cells over-expressing TRPV4 and in native endothelial cells. In rat small mesenteric arteries, apigenin acts on TRPV4 in endothelial cells to induce EDHF-mediated vascular dilatation.

The endothelium: influencing vascular smooth muscle in many ways

The endothelium, although only a single layer of cells lining the vascular and lymphatic systems, contributes in multiple ways to vascular homeostasis. Subsequent to the 1980 report by Robert Furchgott and John Zawadzki, there has been a phenomenal increase in our knowledge concerning the signalling molecules and pathways that regulate endothelial - vascular smooth muscle communication. It is now recognised that the endothelium is not only an important source of nitric oxide (NO), but also numerous other signalling molecules, including the putative endothelium-derived hyperpolarizing factor (EDHF), prostacyclin (PGI(2)), and hydrogen peroxide (H(2)O(2)), which have both vasodilator and vasoconstrictor properties. In addition, the endothelium, either via transferred chemical mediators, such as NO and PGI(2), and (or) low-resistance electrical coupling through myoendothelial gap junctions, modulates flow-mediated vasodilatation as well as influencing mitogenic activity, platelet aggregation, and neutrophil adhesion. Disruption of endothelial function is an early indicator of the development of vascular disease, and thus an important area for further research and identification of potentially new therapeutic targets. This review focuses on the signalling pathways that regulate endothelial - vascular smooth muscle communication and the mechanisms that initiate endothelial dysfunction, particularly with respect to diabetic vascular disease.

Calcium and endothelium-mediated vasodilator signaling

Vascular tone refers to the balance between arterial constrictor and dilator activity. The mechanisms that underlie tone are critical for the control of haemodynamics and matching circulatory needs with metabolism, and thus alterations in tone are a primary factor for vascular disease etiology. The dynamic spatiotemporal control of intracellular Ca(2+) levels in arterial endothelial and smooth muscle cells facilitates the modulation of multiple vascular signaling pathways. Thus, control of Ca(2+) levels in these cells is integral for the maintenance of tone and blood flow, and intimately associated with both physiological and pathophysiological states. Hence, understanding the mechanisms that underlie the modulation of vascular Ca(2+) activity is critical for both fundamental knowledge of artery function, and for the development of targeted therapies. This brief review highlights the role of Ca(2+) signaling in vascular endothelial function, with a focus on contact-mediated vasodilator mechanisms associated with endothelium-derived hyperpolarization and the longitudinal conduction of responses over distance.

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.

Depletion of intracellular Ca2+ stores stimulates the translocation of vanilloid transient receptor potential 4-c1 heteromeric channels to the plasma membrane

OBJECTIVE

To examine the effect of Ca(2+) store depletion on the translocation of vanilloid transient receptor potential (TRPV) 4-C1 heteromeric channels to the plasma membrane.

METHODS AND RESULTS

Vesicular trafficking is a key mechanism for controlling the surface expression of TRP channels in the plasma membrane, where they perform their function. TRP channels in vivo are often composed of heteromeric subunits. Experiments using total internal fluorescence reflection microscopy and biotin surface labeling show that Ca(2+) store depletion enhanced TRPV4-C1 translocation into the plasma membrane in human embryonic kidney 293 cells that were coexpressed with TRPV4 and canonical transient receptor potential 1 (TRPC1). Fluorescent Ca(2+) measurement and patch clamp studies demonstrated that Ca(2+) store depletion enhanced 4α-PDD-stimulated Ca(2+) influx and cation current. The translocation required stromal interacting molecule 1 (STIM1). TRPV4-C1 heteromeric channels were more favorably translocated to the plasma membrane than TRPC1 or TRPV4 homomeric channels. Similar results were obtained in native vascular endothelial cells.

CONCLUSIONS

Ca(2+) store depletion stimulates the insertion of TRPV4-C1 heteromeric channels into the plasma membrane, resulting in an augmented Ca(2+) influx in response to flow in the human embryonic kidney cell overexpression system and native endothelial cells.

Functional Role of Vanilloid Transient Receptor Potential 4-Canonical Transient Receptor Potential 1 Complex in Flow-Induced Ca 2+ Influx

Objective— The present study is aimed at investigating the interaction of TRPV4 with TRPC1 and the functional role of such an interaction in flow-induced Ca 2+ influx. Hemodynamic blood flow is an important physiological factor that modulates vascular tone. One critical early event in this process is a cytosolic Ca 2+ ([Ca 2+ ] i ) rise in endothelial cells in response to flow.

Methods and Results— With the use of fluorescence resonance energy transfer, coimmunoprecipitation, and subcellular colocalization methods, it was found that TRPC1 interacts physically with TRPV4 to form a complex. In functional studies, flow elicited a transient [Ca 2+ ] i increase in TRPV4-expressing human embryonic kidney (HEK) 293 cells. Coexpression of TRPC1 with TRPV4 markedly prolonged this [Ca 2+ ] i transient; it also enabled this [Ca 2+ ] i transient to be negatively modulated by protein kinase G. Furthermore, this flow-induced [Ca 2+ ] i increase was markedly inhibited by anti–TRPC1-blocking antibody T1E3 and a dominant-negative construct TRPC1Δ567-793 in TRPV4-C1–coexpressing HEK cells and human umbilical vein endothelial cells. T1E3 also inhibited flow-induced vascular dilation in isolated rat small mesenteric artery segments.

Conclusion— This study shows that TRPC1 interacts physically with TRPV4 to form a complex, and this TRPV4-C1 complex may mediate flow-induced Ca 2+ influx in vascular endothelial cells. The association of TRPC1 with TRPV4 prolongs the flow-induced [Ca 2+ ] i transient, and it also enables this [Ca 2+ ] i transient to be negatively modulated by protein kinase G. This TRPV4-C1 complex plays a key role in flow-induced endothelial Ca 2+ influx.

Blood ammonia levels in liver cirrhosis: a clue for the presence of portosystemic collateral veins

BACKGROUND

Portal hypertension leads to the formation of portosystemic collateral veins in liver cirrhosis. The resulting shunting is responsible for the development of portosystemic encephalopathy. Although ammonia plays a certain role in determining portosystemic encephalopathy, the venous ammonia level has not been found to correlate with the presence or severity of this entity. So, it has become partially obsolete. Realizing the need for non-invasive markers mirroring the presence of esophageal varices in order to reduce the number of endoscopy screening, we came back to determine whether there was a correlation between blood ammonia concentrations and the detection of portosystemic collateral veins, also evaluating splenomegaly, hypersplenism (thrombocytopenia) and the severity of liver cirrhosis.

METHODS

One hundred and fifty three consecutive patients with hepatic cirrhosis of various etiologies were recruited to participate in endoscopic and ultrasonography screening for the presence of portosystemic collaterals mostly esophageal varices, but also portal hypertensive gastropathy and large spontaneous shunts.

RESULTS

Based on Child-Pugh classification, the median level of blood ammonia was 45 mcM/L in 64 patients belonging to class A, 66 mcM/L in 66 patients of class B and 108 mcM/L in 23 patients of class C respectively (p < 0.001).The grade of esophageal varices was concordant with venous ammonia levels (rho 0.43, p < 0.001). The best area under the curve was given by ammonia concentrations, i, e., 0.78, when comparing areas of ammonia levels, platelet count and spleen longitudinal diameter at ultrasonography. Ammonia levels predicted hepatic decompensation and ascites presence (Odds Ratio 1.018, p < 0.001).

CONCLUSION

Identifying cirrhotic patients with high blood ammonia concentrations could be clinically useful, as high levels would lead to suspicion of being in presence of collaterals, in clinical practice of esophageal varices, and pinpoint those patients requiring closer follow-up and endoscopic screening.

TRPC1 Associates With BK Ca Channel to Form a Signal Complex in Vascular Smooth Muscle Cells

TRPC1 (transient receptor potential canonical 1) is a Ca 2+ -permeable cation channel involved in diverse physiological function. TRPC1 may associate with other proteins to form a signaling complex, which is crucial for channel function. In the present study, we investigated the interaction between TRPC1 and large conductance Ca 2+ -sensitive K + channel (BK Ca ). With the use of potentiometric fluorescence dye DiBAC 4 (3), we found that store-operated Ca 2+ influx resulted in membrane hyperpolarization of vascular smooth muscle cells (VSMCs). The hyperpolarization was inhibited by an anti-TRPC1 blocking antibody T1E3 and 2 BK Ca channel blockers, charybdotoxin and iberiotoxin. These data were confirmed by sharp microelectrode measurement of membrane potential in VSMCs of intact arteries. Furthermore, T1E3 treatment markedly enhanced the membrane depolarization and contraction of VSMCs in response to several contractile agonists including phenylephrine, endothelin-1, and U-46619. In coimmunoprecipitation experiments, an antibody against BK Ca α-subunit [BK Ca (α)] could pull down TRPC1, and moreover an anti-TRPC1 antibody could reciprocally pull down BK Ca (α). Double-labeling immunocytochemistry showed that TRPC1 and BK Ca were colocalized in the same subcellular regions, mainly on the plasma membrane, in VSMCs. These data suggest that, TRPC1 physically associates with BK Ca in VSMCs and that Ca 2+ influx through TRPC1 activates BK Ca to induce membrane hyperpolarization. The hyperpolarizing effect of TRPC1-BK Ca coupling could serve to reduce agonist-induced membrane depolarization, thereby preventing excessive contraction of VSMCs to contractile agonists.

Connexins in vascular physiology and pathology

Cellular interaction in blood vessels is maintained by multiple communication pathways, including gap junctions. They consist of intercellular channels ensuring direct interaction between endothelial and smooth muscle cells and the synchronization of their behavior along the vascular wall. Gap-junction channels arise from the docking of two hemichannels or connexons, formed by the assembly of six connexins, and achieve direct cellular communication by allowing the transport of small metabolites, second messengers, and ions between two adjacent cells. Physiologic variations in connexin expression are observed along the vascular tree, with most common connexins being Cx37, Cx40, and Cx43. Changes in the level of expression of connexins have been correlated to the development of vascular disease, such as hypertension, atherosclerosis, or restenosis. Recent studies on connexin-deficient mice highlighted key roles of these communication pathways in the development of these pathologies and confirmed the need for targeted pharmacologic approaches for their prevention and treatment. The aim of this issue is to review the current knowledge on the implication of gap junctions in vascular function and most common cardiovascular diseases.

17beta-estradiol inhibits calcium-dependent and -independent contractions in isolated human saphenous vein

Studies suggest that estrogen modulate vascular reactivity but at present its exact mechanism of action has yet to be clarified. The aim of this study was to evaluate the effect of 17beta-estradiol (E2) on calcium-dependent and -independent contractions induced in the human saphenous veins (HSVs). HSVs were obtained from patients undergoing coronary artery bypass graft surgery. The ability of E2 to modulate Ca(2+) entry was assessed by obtaining concentration-response curve to CaCl(2) in the absence or presence of E2. In other experiments intracellular Ca(2+) was depleted by repeated application of phenylephrine in the presence of cyclopiazonic acid (CPA). Then, at the plateau of PGF(2alpha) contraction, E2 or nifedipine (NIF) was added. Involvement of protein kinase C (PKC) in relaxant effect of E2 was evaluated by application of phorbol-12,13-dibutyrate (PDBu) in normal or Ca(2+)-free Krebs' solution. When the contraction was obtained, E2 or NIF was added. In Ca(2+)-free hyperpolarizing solution, pretreatment with E2, concentration dependently reduced contractions induced by cumulative addition of calcium chloride. Furthermore, E2 elicited relaxant effects on the PGF(2alpha)-induced contractions in Ca(2+)-free solution in the presence or absence of CPA. Both E2 and NIF produced significant relaxation in HSV rings contracted by direct activation of PKC in Krebs' solution. However, in Ca(2+)-free solution, NIF failed to induce relaxant effect but E2 kept its effect on the PDBu-induced contraction. These results suggest that the relaxant effect of E2 on HSV is elicited by calcium-dependent and -independent pathways. The calcium-independent pathway may involve PKC inhibition.

Flow-induced enhancement of vasoconstriction and blockade of endothelium-derived hyperpolarizing factor (EDHF) by ascorbate in the rat mesentery

BACKGROUND AND PURPOSE

We previously reported that ascorbate inhibits flow- and agonist-induced, EDHF-mediated vasodilatation in the bovine ciliary circulation. This study examined whether ascorbate had similar actions in the rat mesenteric vasculature.

EXPERIMENTAL APPROACH

The effects of ascorbate were examined both in rat second order mesenteric arterial rings suspended in a static wire myograph and the rat mesentery perfused at different rates of flow.

KEY RESULTS

Ascorbate (50 microM) had no effect on U46619-induced tone or acetylcholine-induced, EDHF-mediated vasodilatation in either rings of mesenteric artery or the perfused mesentery at rates of flow below 10 ml min(-1). At higher rates of flow, ascorbate produced two distinct effects in the rat mesentery: a rapid and maintained enhancement of vasoconstrictor tone and a slow (max at 3 h) inhibition of acetylcholine-induced, EDHF-mediated vasodilatation. The enhancement of vasoconstrictor tone appeared to be due to inhibition of flow-induced EDHF-like activity, since it was endothelium-dependent, but could be elicited during blockade of nitric oxide synthase and cyclooxygenase. Despite this, the classical inhibitors of EDHF, apamin and charybdotoxin, failed to affect the ascorbate-induced enhancement of tone, although they inhibited acetylcholine-induced vasodilatation.

CONCLUSIONS AND IMPLICATIONS

Ascorbate inhibits both flow- and agonist-induced EDHF in the rat mesentery. The strikingly different timecourses of these two effects, together with their differential sensitivity to apamin and charybdotoxin, suggest that the flow- and agonist-induced EDHFs in the rat mesenteric vasculature may either be different entities or operate by different mechanisms.

Spreading dilatation to luminal perfusion of ATP and UTP in rat isolated small mesenteric arteries

Levels of ATP achieved within the lumen of vessels suggest a key autacoid role. P2Y receptors on the endothelium may represent the target for ATP, leading to hyperpolarization and associated relaxation of vascular smooth muscle through the endothelium-dependent hyperpolarizing factor (EDHF) pathway. EDHF signals radially from the endothelium to cause dilatation, and appears mechanistically distinct from the axial spread of dilatation, which we showed occurs independently of a change in endothelial cell Ca2+ in rat mesenteric arteries. Here we have investigated the potential of P2Y receptor stimulation to evoke spreading dilatation in rat resistance small arteries under physiological pressure and flow. Triple cannulation of isolated arteries enables focal application of purine and pyrimidine nucleotides to the endothelium, avoiding potential complicating actions of these agents on the smooth muscle. Nucleotides were locally infused through one branch of a bifurcation, causing near maximal local dilatation attributable to EDHF. Dilatation then spread rapidly into the adjacent feed artery and upstream against the direction of luminal flow, sufficient to increase flow into the feed artery. The rate of decay of this spreading dilatation was identical between nucleotides, and matched that to ACh, which acts only on the endothelium. In contrast, focal abluminal application of either ATP or UTP at the downstream end of cannulated arteries evoked constriction, which only in the case of ATP was also associated with modest spread of dilatation. The non-hydrolysable ADP analogue, ADPbetaS, acting at P2Y1 receptors, caused robust local and spreading dilatation responses whether applied to the luminal or abluminal surface of pressurized arteries. Dilatation to nucleotides was sensitive to inhibition with apamin and TRAM-34, selective blockers of small- and intermediate-conductance Ca2+-activated K+ channels, respectively. These data demonstrate that direct luminal stimulation of P2Y receptor on the endothelium of rat mesenteric arteries leads to marked spreading dilatation and thus suggests that circulating purines and pyrimidines may act as important regulators of blood flow.

Novel nitric oxide synthase--dependent mechanism of vasorelaxation in small arteries from hypertensive rats

To determine the mechanism(s) involved in vasorelaxation of small arteries from hypertensive rats, normotensive (NORM), angiotensin II-infused (ANG), high-salt (HS), ANG high-salt (ANG/HS), placebo, and deoxycorticosterone acetate-salt rats were studied. Third-order mesenteric arteries from ANG or ANG/HS displayed decreased sensitivity to acetylcholine (ACh)-induced vasorelaxation compared with NORM or HS, respectively. Maximal relaxations were comparable between groups. Blockade of Ca(2+)-activated K(+) channels had no effect on ANG versus blunting relaxation in NORM (log EC(50): -6.8+/-0.1 versus -7.2+/-0.1 mol/L). NO synthase (NOS) inhibition abolished ACh-mediated relaxation in small arteries from ANG, ANG/HS, and deoxycorticosterone acetate-salt versus blunting relaxation in NORM, HS, and placebo (% maximal relaxation: ANG: 2.7+/-1.8; ANG/HS: 7.2+/-3.2; NORM: 91+/-3.1; HS: 82.1+/-13.3; deoxycorticosterone acetate-salt: 35.2+/-17.7; placebo: 79.3+/-10.3), indicating that NOS is the primary vasorelaxation pathway in these arteries from hypertensive rats. We hypothesized that NO/cGMP signaling and NOS-dependent H(2)O(2) maintains vasorelaxation in small arteries from ANG. ACh increased NOS-dependent cGMP production, indicating that NO/cGMP signaling is present in small arteries from ANG (55.7+/-6.9 versus 30.5+/-5.1 pmol/mg), and ACh stimulated NOS-dependent H(2)O(2) production (ACh: 2.8+/-0.2 micromol/mg; N(omega)-nitro-l-arginine methyl ester hydrochloride+ACh: 1.8+/-0.1 micromol/mg) in small arteries from ANG. H(2)O(2) induced vasorelaxation and catalase blunted ACh-mediated vasorelaxation. In conclusion, Ca(2+)-activated K(+) channel-mediated relaxation is dysfunctional in small mesenteric arteries from hypertensive rats, and the NOS pathway compensates to maintain vasorelaxation in these arteries through NOS-mediated cGMP and H(2)O(2) production.

Endothelium-dependent hyperpolarizations: past beliefs and present facts

Endothelium-dependent relaxations are attributed to the release of various factors, such as nitric oxide, carbon monoxide, reactive oxygen species, adenosine, peptides and arachidonic acid metabolites derived from the cyclooxygenases, lipoxygenases, and cytochrome P450 monooxygenases pathways. The hyperpolarization of the smooth muscle cell can contribute to or be an integral part of the mechanisms underlying the relaxations elicited by virtually all these endothelial mediators. These endothelium-derived factors can activate different families of K(+) channels of the vascular smooth muscle. Other events associated with the hyperpolarization of both the endothelial and the vascular smooth muscle cells (endothelium-derived hyperpolarizing factor (EDHF)-mediated responses) contribute also to endothelium-dependent relaxations. These responses involve an increase in the intracellular Ca(2+) concentration of the endothelial cells followed by the opening of Ca(2+)-activated K(+) channels of small and intermediate conductance and the subsequent hyperpolarization of these cells. Then, the endothelium-dependent hyperpolarization of the underlying smooth muscle cells can be evoked by direct electrical coupling through myoendothelial junctions and/or the accumulation of K(+) ions in the intercellular space between the two cell types. These various mechanisms are not necessarily mutually exclusive and, depending on the vascular bed and the experimental conditions, can occur simultaneously or sequentially, or also may act synergistically.

Elevated pressure selectively blunts flow-evoked vasodilatation in rat mesenteric small arteries

BACKGROUND AND PURPOSE

The present study investigated mechanisms underlying impaired endothelium-dependent vasodilatation elicited by elevating the intraluminal pressure in rat mesenteric small arteries.

EXPERIMENTAL APPROACH

Arterial segments (internal diameter 316+/-2 microm, n=86) were mounted in a pressure myograph. The effect of elevating pressure from 50 to 120 mmHg for 1 h before resetting it to 50 mmHg was studied on endothelium-dependent vasodilatation.

KEY RESULTS

In arteries constricted with U46619 in the presence of indomethacin, shear stress generated by flow, evoked vasodilatation that was abolished by an inhibitor of nitric oxide (NO) synthase, asymmetric dimethylarginine (1 mM), whereas acetylcholine-induced vasodilatation was unchanged. After elevation of intraluminal pressure for 1 h and then resetting it to 50 mmHg, vasodilatation induced by shear stress and the NO donor, S-nitrosopenicillamine was inhibited, while vasodilatation induced by a guanylyl cyclase activator, BAY 412272, and acetylcholine was unaltered. Superoxide levels sensitive to polyethylene glycol superoxide dismutase were increased in segments exposed to elevated pressure. A superoxide scavenger, tempol (300 microM), a general endothelin receptor antagonist, SB 217242 and the selective ET(A) receptor antagonist, BQ 123 preserved shear stress-evoked vasodilatation.

CONCLUSIONS AND IMPLICATIONS

The present study shows that transient exposure to an elevated intraluminal pressure selectively inhibits flow-evoked NO-mediated vasodilatation, probably through activation of endothelin receptors and increased formation of superoxide. In contrast, elevation of pressure did not affect the acetylcholine-evoked endothelium-derived hyperpolarizing factor type vasodilatation in mesenteric small arteries.