Evidence for the expression of multiple uracil nucleotide-stimulated P2 receptors coupled to smooth muscle contraction in porcine isolated arteries

Purinergic signalling in the cardiovascular system-a tribute to Geoffrey Burnstock

Geoffrey Burnstock made groundbreaking discoveries on the physiological roles of purinergic receptors and led on P2 purinergic receptor classification. His knowledge, vision and leadership inspired and influenced the international scientific community. I had the privilege of spending over 10 years (from 1985) with Geoff at the Department of Anatomy and Developmental Biology, initially as a PhD student and then as a postdoctoral research fellow. I regarded him with enormous admiration and affection. This review on purinergic signalling in the cardiovascular system is a tribute to Geoff. It includes some personal recollections of Geoff.

Targeting Purinergic Signaling and Cell Therapy in Cardiovascular and Neurodegenerative Diseases

Extracellular purines exert several functions in physiological and pathophysiological mechanisms. ATP acts through P2 receptors as a neurotransmitter and neuromodulator and modulates heart contractility, while adenosine participates in neurotransmission, blood pressure, and many other mechanisms. Because of their capability to differentiate into mature cell types, they provide a unique therapeutic strategy for regenerating damaged tissue, such as in cardiovascular and neurodegenerative diseases. Purinergic signaling is pivotal for controlling stem cell differentiation and phenotype determination. Proliferation, differentiation, and apoptosis of stem cells of various origins are regulated by purinergic receptors. In this chapter, we selected neurodegenerative and cardiovascular diseases with clinical trials using cell therapy and purinergic receptor targeting. We discuss these approaches as therapeutic alternatives to neurodegenerative and cardiovascular diseases. For instance, promising results were demonstrated in the utilization of mesenchymal stem cells and bone marrow mononuclear cells in vascular regeneration. Regarding neurodegenerative diseases, in general, P2X7 and A_2A receptors mostly worsen the degenerative state. Stem cell-based therapy, mainly through mesenchymal and hematopoietic stem cells, showed promising results in improving symptoms caused by neurodegeneration. We propose that purinergic receptor activity regulation combined with stem cells could enhance proliferative and differentiation rates as well as cell engraftment.

On inotropic effects of UTP in the human heart

Uridine 5'-triphosphate (UTP) exerts a positive inotropic effect (PIE) in isolated electrically driven isolated right atrial trabeculae carneae from patients undergoing heart surgery. This review discusses some aspects of the current knowledge on the putative receptor(s) involved and the potential biochemical transduction steps leading to the PIE.

Coronary artery hypoxic vasorelaxation is augmented by perivascular adipose tissue through a mechanism involving hydrogen sulphide and cystathionine-β-synthase

AIM

Hypoxia causes vasodilatation of coronary arteries which protects the heart from ischaemic damage through mechanisms including the generation of hydrogen sulphide (H₂ S), but the influence of the perivascular adipose tissue (PVAT) and myocardium is incompletely understood. This study aimed to determine whether PVAT and the myocardium modulate the coronary artery hypoxic response and whether this involves hydrogen sulphide.

METHODS

Porcine left circumflex coronary arteries were prepared as cleaned segments and with PVAT intact, myocardium intact or both PVAT and myocardium intact, and contractility investigated using isometric tension recording. Immunoblotting was used to measure levels of H₂ S-synthesizing enzymes: cystathionine-β-synthase (CBS), cystathionine γ-lyase (CSE) and 3-mercaptopyruvate sulphurtransferase (MPST).

RESULTS

All three H₂ S-synthesizing enzymes were detected in the artery and myocardium, but only CBS and MPST were detected in PVAT. Hypoxia elicited a biphasic response in cleaned artery segments consisting of transient contraction followed by prolonged relaxation. In arteries with PVAT intact, hypoxic contraction was attenuated and relaxation augmented. In arteries with myocardium intact, hypoxic contraction was attenuated, but relaxation was unaffected. In replacement experiments, replacement of dissected PVAT and myocardium attenuated artery contraction and augmented relaxation to hypoxia, mimicking the effect of in situ PVAT and indicating involvement of a diffusible factor(s). In arteries with intact PVAT, augmentation of hypoxic relaxation was reversed by amino-oxyacetate (CBS inhibitor), but not DL-propargylglycine (CSE inhibitor) or aspartate (inhibits MPST pathway).

CONCLUSION

PVAT augments hypoxic relaxation of coronary arteries through a mechanism involving H₂ S and CBS, pointing to an important role in regulation of coronary blood flow during hypoxia.

Mechanism underlying the contractile activity of UTP in the mammalian heart

We previously reported that uridine 5'-triphosphate (UTP), a pyrimidine nucleoside triphosphate produced a concentration- and time-dependent increase in the contraction force in isolated right atrial preparations from patients undergoing cardiac bypass surgery due to angina pectoris. The stimulation of the force of contraction was sustained rather than transient. In the present study, we tried to elucidate the underlying receptor and signal transduction for this effect of UTP. Therefore, we measured the effect of UTP on force of contraction, phosphorylation of p38 and ERK1/2, in human atrial preparations, atrial preparations from genetically modified mice, cardiomyocytes from adult mice and cardiomyocytes from neonatal rats. UTP exerted a positive inotropic effect in isolated electrically driven left atrial preparations from wild-type (WT) mice and P2Y₂-, P2Y₄- and P2Y₆-receptor knockout mice. Therefore, we concluded that these P2Y receptors did not mediate the inotropic effects of UTP in atrial preparations from mice. However, UTP (like ATP) increased the phosphorylation states of p38 and ERK1/2 in neonatal rat cardiomyocytes, adult mouse cardiomyocytes and human atrial tissue in vitro. U0126, a MEK 1/2- signal cascade inhibitor, attenuated this phosphorylation and the positive inotropic effects of UTP in murine and human atrial preparations. We suggest that presently unknown receptors mediate the positive inotropic effect of UTP in murine and human atria. We hypothesize that UTP stimulates inotropy via p38 or ERK1/2 phosphorylation. We speculate that UTP may be a valuable target in the development of new drugs aimed at treating human systolic heart failure.

Uridine Adenosine Tetraphosphate-Induced Coronary Relaxation Is Blunted in Swine With Pressure Overload: A Role for Vasoconstrictor Prostanoids

Plasma levels of the vasoactive substance uridine adenosine tetraphosphate (Up₄A) are elevated in hypertensive patients and Up₄A-induced vascular contraction is exacerbated in various arteries isolated from hypertensive animals, suggesting a potential role of Up₄A in development of hypertension. We previously demonstrated that Up₄A produced potent and partially endothelium-dependent relaxation in the porcine coronary microvasculature. Since pressure-overload is accompanied by structural abnormalities in the coronary microvasculature as well as by endothelial dysfunction, we hypothesized that pressure-overload blunts the coronary vasodilator response to Up₄A, and that the involvement of purinergic receptors and endothelium-derived factors is altered. The effects of Up₄A were investigated using wire-myography in isolated coronary small arteries from Sham-operated swine and swine with prolonged (8 weeks) pressure overload of the left ventricle induced by aortic banding (AoB). Expression of purinergic receptors and endothelium-derived factors was assessed in isolated coronary small arteries using real-time PCR. Up₄A (10^-9 to 10^-5 M) failed to produce contraction in isolated coronary small arteries from either Sham or AoB swine, but produced relaxation in preconstricted arteries, which was significantly blunted in AoB compared to Sham. Blockade of purinergic P1, and P2 receptors attenuated Up₄A-induced coronary relaxation more, while the effect of P2X₁-blockade was similar and the effects of A_2A- and P2Y₁-blockade were reduced in AoB as compared to Sham. mRNA expression of neither A1, A2, A3, nor P2X₁, P2X₇, P2Y₁, P2Y₂, nor P2Y₆-receptors was altered in AoB as compared to Sham, while P2Y₁₂ expression was higher in AoB. eNOS inhibition attenuated Up₄A-induced coronary relaxation in both Sham and AoB. Additional blockade of cyclooxygenase enhanced Up₄A-induced coronary relaxation in AoB but not Sham swine, suggesting the involvement of vasoconstrictor prostanoids. In endothelium-denuded coronary small arteries from normal swine, thromboxane synthase (TxS) inhibition enhanced relaxation to Up₄A compared to endothelium-intact arteries, to a similar extent as P2Y₁₂ inhibition, while the combination inhibition of P2Y₁₂ and TxS had no additional effect. In conclusion, Up₄A-induced coronary relaxation is blunted in swine with AoB, which appears to be due to the production of a vasoconstrictor prostanoid, likely thromboxane A₂.

UDP-sugars activate P2Y14 receptors to mediate vasoconstriction of the porcine coronary artery

Aims

UDP-sugars can act as extracellular signalling molecules, but relatively little is known about their cardiovascular actions. The P2Y₁₄ receptor is a G_i/o-coupled receptor which is activated by UDP-glucose and related sugar nucleotides. In this study we sought to investigate whether P2Y₁₄ receptors are functionally expressed in the porcine coronary artery using a selective P2Y₁₄ receptor agonist, MRS2690, and a novel selective P2Y₁₄ receptor antagonist, PPTN (4,7-disubstituted naphthoic acid derivative).

Methods and results

Isometric tension recordings were used to evaluate the effects of UDP-sugars in porcine isolated coronary artery segments. The effects of the P2 receptor antagonists suramin and PPADS, the P2Y₁₄ receptor antagonist PPTN, and the P2Y₆ receptor antagonist MRS2578, were investigated. Measurement of vasodilator-stimulated phosphoprotein (VASP) phosphorylation using flow cytometry was used to assess changes in cAMP levels. UDP-glucose, UDP-glucuronic acid UDP-N-acetylglucosamine (P2Y₁₄ receptor agonists), elicited concentration-dependent contractions of the porcine coronary artery. MRS2690 was a more potent vasoconstrictor than the UDP-sugars. Concentration dependent contractile responses to MRS2690 and UDP-sugars were enhanced in the presence of forskolin (activator of cAMP), where the level of basal tone was maintained by addition of U46619, a thromboxane A₂ mimetic. Contractile responses to MRS2690 were blocked by PPTN, but not by MRS2578. Contractile responses to UDP-glucose were also attenuated by PPTN and suramin, but not by MRS2578. Forskolin-induced VASP-phosphorylation was reduced in porcine coronary arteries exposed to UDP-glucose and MRS2690, consistent with P2Y₁₄ receptor coupling to G_i/o proteins and inhibition of adenylyl cyclase activity.

Conclusions

Our data support a role of UDP-sugars as extracellular signalling molecules and show for the first time that they mediate contraction of porcine coronary arteries via P2Y₁₄ receptors.

Altered expression of P2Y2 and P2X7 purinergic receptors in the isolated rat heart mediates ischemia-reperfusion injury

The aim of this study is to analyze the expression of purinergic receptors in the heart after ischemia-reperfusion, and their possible role in ischemia-reperfusion injury. Rat hearts were perfused according to the Langendorff technique and subjected to 30 min ischemia followed by 15 min reperfusion. Ischemia-reperfusion reduced the gene expression and protein content of purinergic receptors of the P2Y2 subtype, and increased the gene expression and protein content of the P2X7 subtype. Treatment with the agonist of the P2Y2 subtype 2-thio-UTP and with the antagonist of the P2X7 subtype Brilliant Blue improved myocardial function parameters, reduced cell death and increased the myocardial expression of antiapoptotic markers after ischemia-reperfusion. These results suggest that the myocardial expression of the protective P2Y2 subtype of purinergic receptors is reduced, whereas that of the harmful subtype P2X7 subtype is increased during coronary ischemia-reperfusion. This may contribute to myocardial injury in this condition.

Purinergic transmission in blood vessels

There are nineteen different receptor proteins for adenosine, adenine and uridine nucleotides, and nucleotide sugars, belonging to three families of G protein-coupled adenosine and P2Y receptors, and ionotropic P2X receptors. The majority are functionally expressed in blood vessels, as purinergic receptors in perivascular nerves, smooth muscle and endothelial cells, and roles in regulation of vascular contractility, immune function and growth have been identified. The endogenous ligands for purine receptors, ATP, ADP, UTP, UDP and adenosine, can be released from different cell types within the vasculature, as well as from circulating blood cells, including erythrocytes and platelets. Many purine receptors can be activated by two or more of the endogenous ligands. Further complexity arises because of interconversion between ligands, notably adenosine formation from the metabolism of ATP, leading to complex integrated responses through activation of different subtypes of purine receptors. The enzymes responsible for this conversion, ectonucleotidases, are present on the surface of smooth muscle and endothelial cells, and may be coreleased with neurotransmitters from nerves. What selectivity there is for the actions of purines/pyrimidines comes from differential expression of their receptors within the vasculature. P2X1 receptors mediate the vasocontractile actions of ATP released as a neurotransmitter with noradrenaline (NA) from sympathetic perivascular nerves, and are located on the vascular smooth muscle adjacent to the nerve varicosities, the sites of neurotransmitter release. The relative contribution of ATP and NA as functional cotransmitters varies with species, type and size of blood vessel, neuronal firing pattern, the tone/pressure of the blood vessel, and in ageing and disease. ATP is also a neurotransmitter in non-adrenergic non-cholinergic perivascular nerves and mediates vasorelaxation via smooth muscle P2Y-like receptors. ATP and adenosine can act as neuromodulators, with the most robust evidence being for prejunctional inhibition of neurotransmission via A1 adenosine receptors, but also prejunctional excitation and inhibition of neurotransmission via P2X and P2Y receptors, respectively. P2Y2, P2Y4 and P2Y6 receptors expressed on the vascular smooth muscle are coupled to vasocontraction, and may have a role in pathophysiological conditions, when purines are released from damaged cells, or when there is damage to the protective barrier that is the endothelium. Adenosine is released during hypoxia to increase blood flow via vasodilator A2A and A2B receptors expressed on the endothelium and smooth muscle. ATP is released from endothelial cells during hypoxia and shear stress and can act at P2Y and P2X4 receptors expressed on the endothelium to increase local blood flow. Activation of endothelial purine receptors leads to the release of nitric oxide, hyperpolarising factors and prostacyclin, which inhibits platelet aggregation and thus ensures patent blood flow. Vascular purine receptors also regulate endothelial and smooth muscle growth, and inflammation, and thus are involved in the underlying processes of a number of cardiovascular diseases.

Mechanisms underlying uridine adenosine tetraphosphate-induced vascular contraction in mouse aorta: Role of thromboxane and purinergic receptors

Uridine adenosine tetraphosphate (Up4A), a novel endothelium-derived vasoactive agent, is proposed to play a role in cardiovascular disorders and induces aortic contraction through activation of cyclooxygenases (COXs). We and others demonstrated that activation of A1 or A3 adenosine receptors (ARs) results in vascular contraction via thromboxane (TX) A2 production. However, the mechanisms of Up4A-induced vascular contraction in mouse aorta are not understood. We hypothesize that Up4A-induced aortic contraction is through COX-derived TXA2 production, which requires activation of A1 and/or A3AR. Concentration responses to Up4A were conducted in isolated aorta. The TXB2 production, a metabolite of TXA2, was also measured. Up4A (10(-9)-10(-5)M) produced a concentration-dependent contraction >70%, which was markedly attenuated by COX and COX1 but not by COX2 inhibition. Notably, Up4A-induced aortic contraction was blunted by both TX synthase inhibitor ozagrel and TXA2 receptor (TP) antagonist SQ29548. Surprisingly, A3AR deletion had no effect on Up4A-induced contraction. Moreover, A1AR deletion or antagonism as well as A1/A3AR deletion potentiated Up4A-induced aortic contraction, suggesting a vasodilator influence of A1AR. In contrast, non-selective purinergic P2 receptor antagonist PPADS significantly blunted Up4A-induced aortic contraction to a similar extent as selective P2X1R antagonist MRS2159, the latter of which was further reduced by addition of ozagrel. Endothelial denudation almost fully attenuated Up4A-induced contraction. Furthermore, Up4A (3μM) increased TXB2 formation, which was inhibited by either MRS2159 or ozagrel. In conclusion, Up4A-induced aortic contraction depends on activation of TX synthase and TP, which partially requires the activation of P2X1R but not A1 or A3AR through an endothelium-dependent mechanism.

P2Y₂ receptor activation decreases blood pressure via intermediate conductance potassium channels and connexin 37

AIMS

Nucleotides are important paracrine regulators of vascular tone. We previously demonstrated that activation of P2Y₂ receptors causes an acute, NO-independent decrease in blood pressure, indicating this signalling pathway requires an endothelial-derived hyperpolarization (EDH) response. To define the mechanisms by which activation of P2Y₂ receptors initiates EDH and vasodilation, we studied intermediate-conductance (KCa3.1, expressed in endothelial cells) and big-conductance potassium channels (KCa1.1, expressed in smooth muscle cells) as well as components of the myoendothelial gap junction, connexins 37 and 40 (Cx37, Cx40), all hypothesized to be part of the EDH response.

METHODS

We compared the effects of a P2Y₂/₄ receptor agonist in wild-type (WT) mice and in mice lacking KCa3.1, KCa1.1, Cx37 or Cx40 under anaesthesia, while monitoring intra-arterial blood pressure and heart rate.

RESULTS

Acute activation of P2Y₂/₄ receptors (0.01-3 mg kg(-1) body weight i.v.) caused a biphasic blood pressure response characterized by a dose-dependent and rapid decrease in blood pressure in WT (maximal response % of baseline at 3 mg kg(-1) : -38 ± 1%) followed by a consecutive increase in blood pressure (+44 ± 11%). The maximal responses in KCa3.1(-/-) and Cx37(-/-) were impaired (-13 ± 5, +17 ± 7 and -27 ± 1, +13 ± 3% respectively), whereas the maximal blood pressure decrease in response to acetylcholine at 3 μg kg(-1) was not significantly different (WT: -53 ± 3%; KCa3.1(-/-) : -52 ± 3; Cx37(-/-) : -53 ± 3%). KCa1.1(-/-) and Cx40(-/-) showed an identical biphasic response to P2Y2/4 receptor activation compared to WT.

CONCLUSIONS

The data suggest that the P2Y2/4 receptor activation elicits blood pressure responses via distinct mechanisms involving KCa3.1 and Cx37.

Cardiac purinergic signalling in health and disease

This review is a historical account about purinergic signalling in the heart, for readers to see how ideas and understanding have changed as new experimental results were published. Initially, the focus is on the nervous control of the heart by ATP as a cotransmitter in sympathetic, parasympathetic, and sensory nerves, as well as in intracardiac neurons. Control of the heart by centers in the brain and vagal cardiovascular reflexes involving purines are also discussed. The actions of adenine nucleotides and nucleosides on cardiomyocytes, atrioventricular and sinoatrial nodes, cardiac fibroblasts, and coronary blood vessels are described. Cardiac release and degradation of ATP are also described. Finally, the involvement of purinergic signalling and its therapeutic potential in cardiac pathophysiology is reviewed, including acute and chronic heart failure, ischemia, infarction, arrhythmias, cardiomyopathy, syncope, hypertrophy, coronary artery disease, angina, diabetic cardiomyopathy, as well as heart transplantation and coronary bypass grafts.

Effects of NAD at purine receptors in isolated blood vessels

Nicotinamide adenine dinucleotide (NAD) belongs to the family of naturally occurring adenine dinucleotides, best known for their various intracellular roles. However, there is evidence that they can also be released from cells to act as novel extracellular signalling molecules. Relatively little is known about the extracellular actions of NAD, especially in the cardiovascular system. The present study investigated the actions of NAD in the rat thoracic aorta, porcine coronary artery and porcine mesenteric arteries, mounted in organ baths for isometric tension recording. In the rat thoracic aorta and porcine coronary artery, NAD caused endothelium-independent concentration-dependent vasorelaxations which were unaffected by palmitoylCoA, a P2Y1 receptor antagonist, but which were blocked by CGS15943, a non-selective adenosine receptor antagonist. In the porcine coronary artery, NAD-evoked relaxations were abolished by SCH58261, a selective A2A receptor antagonist. In the rat thoracic aorta, NAD-evoked relaxations were attenuated by A2A receptor antagonism with SCH58261 but were unaffected by an A2B receptor antagonist, MRS1754. In contrast, in the porcine mesenteric artery, NAD-evoked endothelium-independent contractions, which were unaffected by a P2 receptor antagonist, suramin, or by NF449, a P2X1 receptor antagonist, but were attenuated following P2X receptor desensitisation with αβ-meATP. In conclusion, the present results show that NAD can alter vascular tone through actions at purine receptors in three different arteries from two species; its molecular targets differ according to the type of blood vessel.

Novel vasocontractile role of the P2Y₁₄ receptor: characterization of its signalling in porcine isolated pancreatic arteries

BACKGROUND AND PURPOSE

The P2Y₁₄ receptor is the newest member of the P2Y receptor family; it is G(i/o) protein-coupled and is activated by UDP and selectively by UDP-glucose and MRS2690 (2-thiouridine-5'-diphosphoglucose) (7-10-fold more potent than UDP-glucose). This study investigated whether P2Y₁₄ receptors were functionally expressed in porcine isolated pancreatic arteries.

EXPERIMENTAL APPROACH

Pancreatic arteries were prepared for isometric tension recording and UDP-glucose, UDP and MRS2690 were applied cumulatively after preconstriction with U46619, a TxA₂ mimetic. Levels of phosphorylated myosin light chain 2 (MLC2) were assessed with Western blotting. cAMP concentrations were assessed using a competitive enzyme immunoassay kit.

KEY RESULTS

Concentration-dependent contractions with a rank order of potency of MRS2690 (10-fold) > UDP-glucose ≥ UDP were recorded. These contractions were reduced by PPTN {4-[4-(piperidin-4-yl)phenyl]-7-[4-(trifluoromethyl)phenyl]-2-naphthoic acid}, a selective antagonist of P2Y₁₄ receptors, which did not affect responses to UTP. Contraction to UDP-glucose was not affected by MRS2578, a P2Y₆ receptor selective antagonist. Raising cAMP levels and forskolin, in the presence of U46619, enhanced contractions to UDP-glucose. In addition, UDP-glucose and MRS2690 inhibited forskolin-stimulated cAMP levels. Removal of the endothelium and inhibition of endothelium-derived contractile agents (TxA₂, PGF(2α) and endothelin-1) inhibited contractions to UDP glucose. Y-27632, nifedipine and thapsigargin also reduced contractions to the agonists. UDP-glucose and MRS2690 increased MLC2 phosphorylation, which was blocked by PPTN.

CONCLUSIONS AND IMPLICATIONS

P2Y₁₄ receptors play a novel vasocontractile role in porcine pancreatic arteries, mediating contraction via cAMP-dependent mechanisms, elevation of intracellular Ca²⁺ levels, activation of RhoA/ROCK signalling and MLC2, along with release of TxA₂, PGF(2α) and endothelin-1.

Purinergic signaling and blood vessels in health and disease

Purinergic signaling plays important roles in control of vascular tone and remodeling. There is dual control of vascular tone by ATP released as a cotransmitter with noradrenaline from perivascular sympathetic nerves to cause vasoconstriction via P2X1 receptors, whereas ATP released from endothelial cells in response to changes in blood flow (producing shear stress) or hypoxia acts on P2X and P2Y receptors on endothelial cells to produce nitric oxide and endothelium-derived hyperpolarizing factor, which dilates vessels. ATP is also released from sensory-motor nerves during antidromic reflex activity to produce relaxation of some blood vessels. In this review, we stress the differences in neural and endothelial factors in purinergic control of different blood vessels. The long-term (trophic) actions of purine and pyrimidine nucleosides and nucleotides in promoting migration and proliferation of both vascular smooth muscle and endothelial cells via P1 and P2Y receptors during angiogenesis and vessel remodeling during restenosis after angioplasty are described. The pathophysiology of blood vessels and therapeutic potential of purinergic agents in diseases, including hypertension, atherosclerosis, ischemia, thrombosis and stroke, diabetes, and migraine, is discussed.

Blunted coronary vasodilator response to uridine adenosine tetraphosphate in post-infarct remodeled myocardium is due to reduced P1 receptor activation

We previously demonstrated that uridine adenosine tetraphosphate (Up4A) exerts a potent vasodilator effect in the healthy porcine coronary vasculature. Since the coronary microvascular effects of Up4A after myocardial infarction (MI) are unknown, the present study investigated the response to Up4A in coronary microvessels from post-MI remodeled porcine myocardium, and the involvement of purinergic receptor subtypes. Coronary small arteries (diameter ∼150 μm) were dissected from the apex of Sham-operated swine and swine in which MI had been produced 5 weeks earlier by transient (2h) occlusion of the left circumflex coronary artery, and mounted on Mulvany wire myographs. Up4A (10(-9)-10(-5)M) produced coronary vasodilation that was reduced in MI as compared to Sham-operated swine. Up4A-induced vasodilation was reduced by P1 blockade with 8-phenyltheophylline in Sham-operated swine and to a lesser extent in MI, while the attenuation by the A2A receptor blocker SCH58261 was similar in Sham-operated and MI swine. Up4A-induced vasodilation remained unaffected by non-selective P2 receptor antagonist PPADS, but was attenuated by selective P2X1 and P2Y1 receptor antagonists MRS2159 and MRS2179, albeit to a similar extent in Sham-operated and MI swine. These responses were paralleled by similar mRNA expression levels of A2A, P2X1 and P2Y1 receptors in MI compared to slaughterhouse control swine. Finally, attenuation of Up4A-induced coronary vasodilation by nitric oxide synthase inhibition was not attenuated in MI as compared to Sham-operated swine. In conclusion, blunted coronary vasodilation in response to Up4A in MI swine is most likely due to reduced activation of P1, rather than P2, receptors and does not involve a loss of NO bioavailability.

Extracellular UDP enhances P2X-mediated bladder smooth muscle contractility via P2Y(6) activation of the phospholipase C/inositol trisphosphate pathway

Bladder dysfunction characterized by abnormal bladder smooth muscle (BSM) contractions is pivotal to the disease process in overactive bladder, urge incontinence, and spinal cord injury. Purinergic signaling comprises one key pathway in modulating BSM contractility, but molecular mechanisms remain unclear. Here we demonstrate, using myography, that activation of P2Y6 by either UDP or a specific agonist (MRS 2693) induced a sustained increase in BSM tone (up to 2 mN) in a concentration-dependent manner. Notably, activation of P2Y6 enhanced ATP-mediated BSM contractile force by up to 45%, indicating synergistic interactions between P2X and P2Y signaling. P2Y6-activated responses were abolished by phospholipase C (PLC) and inositol trisphosphate (IP3) receptor antagonists U73122 and xestospongin C, demonstrating involvement of the PLC/IP3 signal pathway. Mice null for Entpd1, an ectonucleotidase on BSM, demonstrated increased force generation on P2Y6 activation (150%). Thus, in vivo perturbations to purinergic signaling resulted in altered P2Y6 activity and bladder contractility. We conclude that UDP, acting on P2Y6, regulates BSM tone and in doing so selectively maximizes P2X1-mediated contraction forces. This novel neurotransmitter pathway may play an important role in urinary voiding disorders characterized by abnormal bladder motility.

Uridine adenosine tetraphosphate is a novel vasodilator in the coronary microcirculation which acts through purinergic P1 but not P2 receptors

Uridine adenosine tetraphosphate (Up4A) has been identified as an endothelium-derived contracting factor, which acts through purinergic P2X and P2Y receptors. Since the coronary vascular actions of Up4A are unknown, we investigated the vasoactive profile of Up4A in coronary microvessels, and studied the involvement of purinergic receptor subtypes. Studies were performed in isolated porcine coronary small arteries (diameter∼250 μm), with and without endothelial denudation, mounted on a Mulvany wire myograph. Purinergic receptor expression was assessed by real-time PCR. Up4A (10(-9)-10(-5) M) failed to induce contraction at basal tone, but produced concentration-dependent vasorelaxation in precontracted microvessels. Up4A was slightly less potent than adenosine, ATP, and ADP in producing vasorelaxation, but significantly more potent than UTP and UDP. mRNA expression of P2X(4), P2Y(1), P2Y(2), P2Y(4), P2Y(6) and A(2A), but not P2X(1), receptors was observed. Up4A-induced vasodilation was unaffected by non-selective P2 receptor antagonist PPADS, P2X(1) antagonist MRS2159, P2Y(1) antagonist MRS2179 and P2Y(6) antagonist MRS2578, but was markedly attenuated by non-selective P1 receptor antagonist 8PT and A(2A) antagonist SCH58261. Up4A-induced vasodilation was not affected by ectonucleotidase inhibitor ARL67156, suggesting that A(2A) stimulation was not the result of Up4A breakdown to adenosine. Up4A-induced vasodilation was blunted in denuded vessels; additional A(2A) receptor blockade further attenuated Up4A-induced vasodilation, suggesting that A(2A) receptor-mediated vasodilation is only partly endothelium-dependent. In conclusion, Up4A exerts a vasodilator rather than a vasoconstrictor influence in coronary microvessels, which is mediated via A(2A) receptors and is partly endothelium-dependent.

P2Y₂ receptor activation decreases blood pressure and increases renal Na⁺ excretion

ATP and UTP are endogenous agonists of P2Y(2/4) receptors. To define the in vivo effects of P2Y(2) receptor activation on blood pressure and urinary excretion, we compared the response to INS45973, a P2Y(2/4) receptor agonist and UTP analog, in wild-type (WT) and P2Y(2) receptor knockout (P2Y(2)-/-) mice. INS45973 was administered intravenously as a bolus injection or continuous infusion to determine effects on blood pressure and renal function, respectively. Within seconds, bolus application of INS45973 (0.1 to 3 mg/kg body wt) dose-dependently decreased blood pressure in WT (maximum response -35 ± 2 mmHg) and to a similar extent in endothelial nitric oxide synthase knockout mice. By contrast, blood pressure increased in P2Y(2)-/- (maximum response +18 ± 1 mmHg) but returned to basal levels within 60 s. Continuous infusion of INS45973 (25 to 750 μg·min(-1)·kg(-1) body wt) dose-dependently increased urinary excretion of Na(+) in WT (maximum response +46 ± 15%) but reduced Na(+) excretion in P2Y(2)-/- (maximum responses of -45 ± 15%) mice. In renal clearance experiments, INS45973 did not affect glomerular filtration rate but lowered blood pressure and increased fractional excretion of fluid, Na(+), and K(+) in WT relative to P2Y(2)-/- mice. The blood pressure responses to INS45973 are consistent with P2Y(2) receptor-mediated NO-independent vasodilation and implicate responses to endothelium-derived hyperpolarizing factor, and P2Y(2) receptor-independent vasoconstriction, probably via activation of P2Y(4) receptors on smooth muscle. Systemic activation of P2Y(2) receptors thus lowers blood pressure and inhibits renal Na(+) reabsorption, effects suggesting the potential utility of P2Y(2) agonism in the treatment of hypertension.

Purinergic receptor type 6 contributes to airway inflammation and remodeling in experimental allergic airway inflammation

RATIONALE

Extracellular nucleotides have recently been identified as proinflammatory mediators involved in asthma pathogenesis by signaling via purinergic receptors, but the role of the purinergic receptor type 6 (P2Y6R) has not been previously investigated.

OBJECTIVES

To investigate the role of P2Y6R in asthma pathogenesis.

METHODS

Acute and chronic OVA model and also HDM model of allergic inflammation in C57Bl/6 mice treated with specific P2Y6R antagonist and P2Y6R(-/-) mice were evaluated for classical features of asthmatic inflammation. In addition, primary epithelial cell culture from human and epithelial cell lines from mouse and human were stimulated with P2Y6R agonist and treated with P2Y6R antagonist and assessed for IL-6, IL-8/CXCL8 and KC levels. Experiments with P2Y6R(-/-) and P2Y6R(+/+) chimera were performed to discriminate the role of P2Y6R activation in structural lung cells and in cells from hematopoietic system.

MEASUREMENTS AND MAIN RESULTS

We observed that the intratracheal application of a P2Y6R antagonist (MRS2578) and P2Y6R deficiency inhibited cardinal features of asthma, such as bronchoalveolar lavage eosinophilia, airway remodeling, Th2 cytokine production, and bronchial hyperresponsiveness in the ovalbumin-alum model. MRS2578 was also effective in reducing airway inflammation in a model using house dust mite extracts to induce allergic lung inflammation. Experiments with bone marrow chimeras revealed the importance of the P2Y6R expression on lung structural cells in airway inflammation. In accordance with this finding, we found a strong up-regulation of P2Y6 expression on airway epithelial cells of animals with experimental asthma. Concerning the underlying mechanism, we observed that MRS2578 inhibited the release of IL-6 and IL-8/KC by lung epithelial cells in vivo, whereas intrapulmonary application of the P2Y6R agonist uridine-5'-diphosphate increased the bronchoalveolar levels of IL-6 and KC. In addition, selective activation of P2Y6 receptors induced the release of IL-6 and KC/IL-8 by murine and human lung epithelial cells in vitro.

CONCLUSIONS

P2Y6R expression on airway epithelial cells is up-regulated during acute and chronic allergic airway inflammation, and selective blocking of P2Y6R or P2Y6R deficiency on the structural cells reduces cardinal features of experimental asthma. Thus, blocking pulmonary P2Y6R might be a target for the treatment of allergic airway inflammation.

Differential effects of uridine adenosine tetraphosphate on purinoceptors in the rat isolated perfused kidney

BACKGROUND AND PURPOSE

Purinergic signalling plays an important role in vascular tone regulation in humans. We have identified uridine adenosine tetraphosphate (Up(4)A) as a novel and highly potent endothelial-derived contracting factor. Up(4)A induces strong vasoconstrictive effects in the renal vascular system mainly by P2X(1) receptor activation. However, other purinoceptors are also involved and were analysed here.

EXPERIMENTAL APPROACH

The rat isolated perfused kidney was used to characterize vasoactive actions of Up(4)A.

KEY RESULTS

After desensitization of the P2X(1) receptor by α,β-methylene ATP (α,β-meATP), Up(4)A showed dose-dependent P2Y(2)-mediated vasoconstriction. Continuous perfusion with Up(4)A evoked a biphasic vasoconstrictor effect: there was a strong and rapidly desensitizing vasoconstriction, inhibited by P2X(1) receptor desensitization. In addition, there is a long-lasting P2Y(2)-mediated vasoconstriction. This vasoconstriction could be blocked by suramin, but not by PPADS or reactive blue 2. In preparations of the rat isolated perfused kidney model with an elevated vascular tone, bolus application of Up(4)A showed a dose-dependent vasoconstriction that was followed by a dose-dependent vasodilation. The vasoconstriction was in part sensitive to P2X(1) receptor desensitization by α,β-meATP, and the remaining P2Y(2)-mediated vasoconstriction was only inhibited by suramin. The Up(4)A-induced vasodilation depended on activation of nitric oxide synthases, and was mediated by P2Y(1) and P2Y(2) receptor activation.

CONCLUSIONS AND IMPLICATIONS

Up(4)A activated P2X(1) and P2Y(2) receptors to act as a vasoconstrictor, whereas endothelium-dependent vasodilation was induced by P2Y(1/2) receptor activation. Up(4)A might be of relevance in the physiology and pathophysiology of vascular tone regulation.

Association of the purinergic receptor P2Y, G-protein coupled, 2 (P2RY2) gene with myocardial infarction in Japanese men

BACKGROUND

Atherosclerosis leads to myocardial infarction (MI) and P2RY2 plays an important role in this process. The aim of the present study was to investigate the association between human P2RY2 and MI via a haplotype-based case-control study that additionally analyzed the group by sex.

METHODS AND RESULTS

The 310 MI patients and 254 controls were genotyped for 5 single-nucleotide polymorphisms (SNPs) of the human P2RY2 gene (rs4944831, rs1783596, rs4944832, rs4382936, rs10898909). Data were separately analyzed for the total, male, and female subjects. For men, the GA+AA genotype of rs10898909 was significantly higher in MI patients as compared with controls (P=0.040). Logistic regression analysis found a significant difference for the genotype (P=0.016). As compared with controls, the frequencies of the C-A and T-C-A haplotypes were significantly higher (P=0.016, and P=0.045, respectively) in men, whereas the frequencies of the C-G and T-A-A haplotypes were significantly lower (P=0.023, and P=0.025, respectively) in MI patients.

CONCLUSIONS

The GA+AA genotype, as well as the C-A and T-C-A haplotypes, of human P2RY2 could be genetic markers for MI in Japanese men.

Myogenic tone in mouse mesenteric arteries: evidence for P2Y receptor-mediated, Na(+), K (+), 2Cl (-) cotransport-dependent signaling

This study examines the action of agonists and antagonists of P2 receptors on mouse mesenteric artery contractions and the possible involvement of these signaling pathways in myogenic tone (MT) evoked by elevated intraluminal pressure. Both ATP and its non-hydrolyzed analog alpha,beta-ATP triggered transient contractions that were sharply decreased in the presence of NF023, a potent antagonist of P2X(1) receptors. In contrast, UTP and UDP elicited sustained contractions which were suppressed by MRS2567, a selective antagonist of P2Y(6) receptors. Inhibition of Na(+), K(+), 2Cl(-) cotransport (NKCC) with bumetanide led to attenuation of contractions in UTP- but not ATP-treated arteries. Both UTP-induced contractions and MT were suppressed by MRS2567 and bumetanide but were insensitive to NF023. These data implicate a P2Y(6)-mediated, NKCC-dependent mechanism in MT of mesenteric arteries. The action of heightened intraluminal pressure on UTP release from mesenteric arteries and its role in the triggering of P2Y(6)-mediated signaling should be examined further.

ATP induces guinea pig gallbladder smooth muscle excitability via the P2Y4 receptor and COX-1 activity

The purpose of this study was to elucidate the mechanisms by which ATP increases guinea pig gallbladder smooth muscle (GBSM) excitability. We evaluated changes in membrane potential and action potential (AP) frequency in GBSM by use of intracellular recording. Application of ATP (100 microM) caused membrane depolarization and a significant increase in AP frequency that were not sensitive to block by tetrodotoxin (0.5 microM). The nonselective P2 antagonist, suramin (100 microM), blocked the excitatory response, resulting in decreased AP frequency in the presence of ATP. The excitatory response to ATP was not altered by pyridoxal-phosphate-6-azophenyl-2,4-disulfonic acid (30 microM), a nonselective P2X antagonist. UTP also caused membrane depolarization and increased AP frequency, with a similar dose-response relationship as ATP. RT-PCR demonstrated that the P2Y(4), but not P2Y(2), receptor subtype is expressed in guinea pig gallbladder muscularis. ATP induced excitation was blocked by indomethacin (10 microM) and the cyclooxygenase (COX)-1 inhibitor SC-560 (300 nM), but not the COX-2 inhibitor nimesulide (500 nM). These data suggest that ATP stimulates P2Y(4) receptors within the gallbladder muscularis and, in turn, stimulate prostanoid production via COX-1 leading to increased excitability of GBSM.

Intestinal inflammation increases the expression of the P2Y6 receptor on epithelial cells and the release of CXC chemokine ligand 8 by UDP

Epithelial cells participate in the immune response of the intestinal mucosa. Extracellular nucleotides have been recognized as inflammatory molecules. We investigated the role of extracellular nucleotides and their associated P2Y receptors in the secretion of cytokines by epithelial cells. The effect of intestinal inflammation on P2Y(6) receptor expression was determined by PCR in the mouse, rat, and human. Localization of the P2Y(6) receptor was determined by immunofluorescence microscopy in the colon of normal and dextran sulfate sodium-treated mice. The effect of P2Y(6) activation by UDP on cytokine expression and release by epithelial cells was determined using a combination of Western blots, luciferase assays, RT-PCR, cytokine Ab arrays, and ELISA. Inflammation up-regulates P2Y(2) as well as P2Y(6) receptor expression in the mucosa of the colon of colitic mice. In vitro, we demonstrated that UDP could be released by Caco-2/15 cells. We have confirmed the increased expression of P2Y(6) by challenging intestinal epithelial cell-6 and Caco-2/15 cells with TNF-alpha and IFN-gamma and showing that stimulation of epithelial cells by UDP results in an increased expression and release of CXCL8 by an ERK1/2-dependent mechanism. The increase in CXCL8 expression was associated with a transcriptional activation by the P2Y(6) receptor. This study is the first report demonstrating the implication of P2Y receptors in the inflammatory response of intestinal epithelial cells. We show for the first time that P2Y(6), as well as P2Y(2), expression is increased by the stress associated with intestinal inflammation. These results demonstrate the emergence of extracellular nucleotide signaling in the orchestration of intestinal inflammation.

P2 purinoceptor-mediated cardioprotection in ischemic-reperfused mouse heart

P2 purinoceptor modulation of injury during ischemia-reperfusion was studied in murine hearts. Effects of P2 agonism or antagonism, and interstitial accumulation of P2 agonists (UTP, ATP, and ADP), were assessed in Langendorff perfused hearts during 20 min of ischemia and 45 min of reperfusion. In control hearts, ventricular pressure development recovered to 68 +/- 4 mm Hg (63 +/- 3% baseline), diastolic pressure remained elevated (23 +/- 2 mm Hg), and 26 +/- 4 U/g lactate dehydrogenase (LDH) was released during reperfusion, evidencing necrosis. Treatment with 250 nM UTP improved pressure development (85 +/- 5 mm Hg, or 77 +/- 2%) and reduced diastolic contracture (by approximately 70%, to 7 +/- 1 mm Hg) and LDH loss (by approximately 60%, to 11 +/- 2 U/g). In contrast, P2Y1 agonism with 50 nM 2-methyl-thio-ATP (2-MeSATP) was ineffective. In the presence of the P2Y antagonist suramin (10 or 200 microM), UTP no longer improved postischemic outcomes. Ischemia also substantially elevated interstitial [UTP], [ATP], and [ADP], potentially activating P2 receptors. This was supported in part by effects of antagonists: 200 microM suramin worsened LDH efflux (53 +/- 9 IU/g) and contractile dysfunction (41 +/- 2 mm Hg diastolic pressure; 28 +/- 3 mm Hg developed pressure), as did P2Y antagonism with either 10 or 100 microM reactive blue 2. However, a 10 microM concentration of suramin failed to alter outcome. P2X antagonism with 10 microM pyridoxal phosphate-6-azo-(benzene-2,4-disulfonic acid and P2X1-selective pyridoxal-alpha5-phosphate-6-phenylazo-4'-carboxylic acid (MRS2159) (30 microM) was ineffective. Data collectively support cardioprotection with low concentrations of UTP, and they are consistent with P2Y2 involvement. Endogenous nucleotides may also play a protective role, as evidenced by effects of P2 antagonists, although this warrants further investigation.