The stable pyrimidines UDPbetaS and UTPgammaS discriminate between the P2 receptors that mediate vascular contraction and relaxation of the rat mesenteric artery

Current Pharmacology and Modulation of the Purinergic System in Takotsubo Syndrome Triggered by Cytokine Storm

Studies show that with the COVID-19 pandemic, the world's population went through multiple stress and anxiety factors, generating serious psychological problems, in addition, the virus also caused damage and physical stress to those contaminated. In this way, the intense emotional experiences and stressful effects on the body caused by SARS-CoV-2 are capable of triggering the excessive release of catecholamines in the body. Thus, the framework of Takotsubo Syndrome is characterized by myocardial dysfunction as a response of cardiac receptors to the spillage of such hormones in an unregulated way in the human body. The purinergic system plays a central role in this process, as it actively participates in actions responsible for the syndromic cascade, such as the stress generated by the cytokine storm triggered by the virus and the stimulation of deregulated catecholamine release. Therefore, further pharmacological studies on the role of purines in this pathology should be developed in order to avoid the evolution of the syndrome and to modulate its P1 and P2 receptors aiming at developing means of reversing or treating the Takotsubo Syndrome.

Purinergic receptors modulators: An emerging pharmacological tool for disease management

Purinergic signaling is mediated through extracellular nucleotides (adenosine 5'-triphosphate, uridine-5'-triphosphate, adenosine diphosphate, uridine-5'-diphosphate, and adenosine) that serve as signaling molecules. In the early 1990s, purines and pyrimidine receptors were cloned and characterized drawing the attention of scientists toward this aspect of cellular signaling. This signaling pathway is comprised of four subtypes of adenosine receptors (P1), eight subtypes of G-coupled protein receptors (P2YRs), and seven subtypes of ligand-gated ionotropic receptors (P2XRs). In current studies, the pathophysiology and therapeutic potentials of these receptors have been focused on. Various ligands, modulating the functions of purinergic receptors, are in current clinical practices for the treatment of various neurodegenerative disorders and cardiovascular diseases. Moreover, several purinergic receptors ligands are in advanced phases of clinical trials as a remedy for depression, epilepsy, autism, osteoporosis, atherosclerosis, myocardial infarction, diabetes, irritable bowel syndrome, and cancers. In the present study, agonists and antagonists of purinergic receptors have been summarized that may serve as pharmacological tools for drug design and development.

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.

Tools and drugs for uracil nucleotide-activated P2Y receptors

P2Y receptors (P2YRs) are a family of G protein-coupled receptors activated by extracellular nucleotides. Physiological P2YR agonists include purine and pyrimidine nucleoside di- and triphosphates, such as ATP, ADP, UTP, UDP, nucleotide sugars, and dinucleotides. Eight subtypes exist, P2Y₁, P2Y₂, P2Y₄, P2Y₆, P2Y₁₁, P2Y₁₂, P2Y₁₃, and P2Y₁₄, which represent current or potential future drug targets. Here we provide a comprehensive overview of ligands for the subgroup of the P2YR family that is activated by uracil nucleotides: P2Y₂ (UTP, also ATP and dinucleotides), P2Y₄ (UTP), P2Y₆ (UDP), and P2Y₁₄ (UDP, UDP-glucose, UDP-galactose). The physiological agonists are metabolically unstable due to their fast hydrolysis by ectonucleotidases. A number of agonists with increased potency, subtype-selectivity and/or enzymatic stability have been developed in recent years. Useful P2Y₂R agonists include MRS2698 (6-01, highly selective) and PSB-1114 (6-05, increased metabolic stability). A potent and selective P2Y₂R antagonist is AR-C118925 (10-01). For studies of the P2Y₄R, MRS4062 (3-15) may be used as a selective agonist, while PSB-16133 (10-06) is a selective antagonist. Several potent P2Y₆R agonists have been developed including 5-methoxyuridine 5'-O-((R_p)α-boranodiphosphate) (6-12), PSB-0474 (3-11), and MRS2693 (3-26). The isocyanate MRS2578 (10-08) is used as a selective P2Y₆R antagonist, although its reactivity and low water-solubility are limiting. With MRS2905 (6-08), a potent and metabolically stable P2Y₁₄R agonist is available, while PPTN (10-14) represents a potent and selective P2Y₁₄R antagonist. The radioligand [³H]UDP can be used to label P2Y₁₄Rs. In addition, several fluorescent probes have been developed. Uracil nucleotide-activated P2YRs show great potential as drug targets, especially in inflammation, cancer, cardiovascular and neurodegenerative diseases.

Current knowledge on the nucleotide agonists for the P2Y2 receptor

P2Y receptors are G-protein-coupled receptors (GPCRs) for extracellular nucleotides. There are eight mammalian P2Y receptor subtypes (P2Y1, P2Y2, P2Y4, P2Y6, P2Y11, P2Y12, P2Y13, and P2Y14). P2Y2 receptors are widely expressed and play important roles in multiple functionalities. Diquafosol tetrasodium, known as INS365, which was the first P2Y2 receptor agonists that had been approved in April 2010 and launched in Japan by Santen Pharmaceuticals. Besides, a series of similar agonists for the P2Y2 receptor are undergoing development to cure different diseases related to the P2Y2 receptor. This article illustrated the structure and functions of the P2Y2 receptor and focused on several kinds of agonists about their molecular structures, research progress and chemical synthesis methods. Last but not the least, we summarized the structures-activity relationship (SAR) of agonists for the P2Y2 receptor and expected more efficient agonists for the P2Y2 receptor.

TLR-Activated Gap Junction Channels Protect Mice against Bacterial Infection through Extracellular UDP Release

Extracellular UDP (eUDP), released as a danger signal by stressed or apoptotic cells, plays an important role in a series of physiological processes. Although the mechanism of eUDP release in apoptotic cells has been well defined, how the eUDP is released in innate immune responses remains unknown. In this study, we demonstrated that UDP was released in both Escherichia coli-infected mice and LPS- or Pam3CSK4-treated macrophages. Also, LPS-induced UDP release could be significantly blocked by selective TLR4 inhibitor Atractylenolide I and selective gap junction inhibitors carbenoxolone and flufenamic acid (FFA), suggesting the key role of TLR signaling and gap junction channels in this process. Meanwhile, eUDP protected mice from peritonitis by reducing invaded bacteria that could be rescued by MRS2578 (selective P2Y6 receptor inhibitor) and FFA. Then, connexin 43, as one of the gap junction proteins, was found to be clearly increased by LPS in a dose- and time-dependent manner. Furthermore, if we blocked LPS-induced ERK signaling by U0126, the expression of connexin 43 and UDP release was also inhibited dramatically. In addition, UDP-induced MCP-1 secretion was significantly reduced by MRS2578, FFA, and P2Y6 mutation. Accordingly, pretreating mice with U0126 and Gap26 increased invaded bacteria and aggravated mice death. Taken together, our study reveals an internal relationship between danger signals and TLR signaling in innate immune responses, which suggests a potential therapeutic significance of gap junction channel-mediated UDP release in infectious diseases.

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.

Expression and characterization of purinergic receptors in rat middle meningeal artery-potential role in migraine

The dura mater and its vasculature have for decades been central in the hypothesis of migraine and headache pathophysiology. Although recent studies have questioned the role of the vasculature as the primary cause, dural vessel physiology is still relevant in understanding the complex pathophysiology of migraine. The aim of the present study was to isolate the middle meningeal artery (MMA) from rodents and characterize their purinergic receptors using a sensitive wire myograph method and RT-PCR. The data presented herein suggest that blood flow through the MMA is, at least in part, regulated by purinergic receptors. P2X1 and P2Y6 receptors are the strongest contractile receptors and, surprisingly, ADPβS caused contraction most likely via P2Y1 or P2Y13 receptors, which is not observed in other arteries. Adenosine addition, however, caused relaxation of the MMA. The adenosine relaxation could be inhibited by SCH58261 (A2A receptor antagonist) and caffeine (adenosine receptor antagonist). This gives one putative molecular mechanism for the effect of caffeine, often used as an adjuvant remedy of cranial pain. Semi-quantitative RT-PCR expression data for the receptors correlate well with the functional findings. Together these observations could be used as targets for future understanding of the in vivo role of purinergic receptors in the MMA.

P2Y₁ and P2Y₁₂ receptors in hypoxia- and adenosine diphosphate-induced pulmonary vasoconstriction in vivo in the pig

PURPOSE

To investigate the role of P2Y₁ and P2Y₁₂ receptors in hypoxia- and adenosine diphosphate (ADP)-induced pulmonary vasoconstriction.

METHODS

19 anaesthetized, mechanically ventilated pigs (31.3 ± 0.7 kg) were evaluated in normoxia and hypoxia, without (n = 6) or with P2Y₁ receptor antagonist MRS2500 (n = 7) or P2Y₁₂ receptor antagonist cangrelor (n = 6) treatment. 12 pigs (29.3 ± 0.4 kg) were evaluated before and during ADP infusion, without and with MRS2500 (n = 6) or cangrelor (n = 6) pre-treatment.

RESULTS

Hypoxia increased (p < 0.05) mean pulmonary artery pressure (MPAP) by 14.2 ± 1.1 mmHg and pulmonary vascular resistance (PVR) by 2.7 ± 0.4 WU. Without treatment MPAP and PVR remained unaltered (p = ns) for 90 min hypoxia. During hypoxia MRS2500 decreased (p < 0.013) MPAP by 4.3 ± 1.2 mmHg within 15 min. Cangrelor decreased (p < 0.036) MPAP to be 3.3 ± 0.4 and 3.6 ± 0.6 mmHg lower than hypoxia baseline after 10 and 30 min. PVR was, however, unaltered (p = ns) by MRS2500 or cangrelor during hypoxia. ADP increased (p < 0.001) MPAP and PVR to stabilize 11.1 ± 1.3 mmHg and 2.7 ± 0.3 WU higher than baseline. MRS2500 or cangrelor pre-treatment totally abolished the sustained MPAP- and PVR-increases to ADP.

CONCLUSIONS

ADP elicits pulmonary vasoconstriction through P2Y₁ and P2Y₁₂ receptor activation. ADP is not a mandatory modulator, but may still contribute to pulmonary vascular tone during acute hypoxia. Further investigations into the mechanisms behind ADP-induced pulmonary vasoconstriction and the role of ADP as a modulator of pulmonary vascular tone during hypoxia are warranted.

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.

Purinergic receptors regulate myogenic tone in cerebral parenchymal arterioles

Myogenic tone is a fundamental aspect of vascular behavior in resistance arteries. This contractile response to changes in intravascular pressure is critically involved in blood flow autoregulation in tissues such as the brain, kidneys, and heart. Myogenic tone also helps regulate precapillary pressure and provides a level of background tone upon which vasodilator stimuli act to increase tissue perfusion when appropriate. Despite the importance of these processes in the brain, little is known about the mechanisms involved in control of myogenic tone in the cerebral microcirculation. Here, we report that pharmacological inhibition of P2Y4 and P2Y6 pyrimidine receptors nearly abolished myogenic tone in cerebral parenchymal arterioles (PAs). Molecular suppression of either P2Y4 or P2Y6 receptors using antisense oligodeoxynucleotides reduced myogenic tone by 44%±8% and 45%±7%, respectively. These results indicate that both receptor isoforms are activated by increased intravascular pressure, which enhances the activity of voltage-dependent calcium channels and increases myogenic tone in PAs. Enhancement or inhibition of ectonucleotidase activity had no effect on parenchymal arteriolar myogenic tone, indicating that this response is not mediated by local release of nucleotides, but rather may involve direct mechanical activation of P2Y receptors in the smooth muscle cells.

Pharmacological characterization of uracil nucleotide-preferring P2Y receptors modulating intestinal motility: a study on mouse ileum

We investigated the possible modulation of the intestinal contractility by uracil nucleotides (UTP and UDP), using as model the murine small intestine. Contractile activity of a mouse ileum longitudinal muscle was examined in vitro as changes in isometric tension. Transcripts encoding for uracil-sensitive receptors was investigated by RT-PCR. UDP induced muscular contractions, sensitive to PPADS, suramin, or MRS 2578, P2Y(6) receptor antagonist, and mimicked by PSB 0474, P2Y(6)-receptor agonist. UTP induced biphasic effects characterized by an early inhibition of the spontaneous contractile activity followed by muscular contraction. UTP excitatory effects were antagonized by PPADS, suramin, but not by MRS 2578, whilst the inhibitory effects were antagonized by PPADS but not by suramin or MRS 2578. UTPγS, P2Y(2)/(4) receptor agonist but not 2-thio-UTP, P2Y(2) receptor agonist, mimicked UTP effects. The inhibitory effects induced by UTP was abolished by ATP desensitization and increased by extracellular acidification. UDP or UTP responses were insensitive to TTX, atropine, or L-NAME antagonized by U-73122, inhibitor of phospholipase C (PLC) and preserved in the presence of nifedipine or low Ca(2+) solution. Transcripts encoding the uracil nucleotide-preferring receptors were expressed in mouse ileum. Functional postjunctional uracil-sensitive receptors are present in the longitudinal muscle of the mouse ileum. Activation of P2Y(6) receptors induces muscular contraction, whilst activation of P2Y(4) receptors leads to inhibition of the contractile activity. Indeed, the presence of atypical UTP-sensitive receptors leading to muscular contraction is suggested. All uracil-sensitive receptors are linked to the PLC pathway.

Alterations in vasoconstrictor responses to the endothelium-derived contracting factor uridine adenosine tetraphosphate are region specific in DOCA-salt hypertensive rats

Uridine adenosine tetraphosphate (Up(4)A) has been recently identified as a novel and potent endothelium-derived contracting factor and contains both purine and pyrimidine moieties, which activate purinergic P2X and P2Y receptors. The present study was designed to compare contractile responses to Up(4)A and other nucleotides such as ATP (P2X/P2Y agonist), UTP (P2Y(2)/P2Y(4) agonist), UDP (P2Y(6) agonist), and α,β-methylene ATP (P2X(1) agonist) in different vascular regions [thoracic aorta, basilar, small mesenteric, and femoral arteries] from deoxycorticosterone acetate-salt (DOCA-salt) and control rats. In DOCA-salt rats [vs. control uninephrectomized (Uni) rats]: (1) in thoracic aorta, Up(4)A-, ATP-, and UTP-induced contractions were unchanged; (2) in basilar artery, Up(4)A-, ATP-, UTP- and UDP-induced contractions were increased, and expression for P2X(1), but not P2Y(2) or P2Y(6) was decreased; (3) in small mesenteric artery, Up(4)A-induced contraction was decreased and UDP-induced contraction was increased; expression of P2Y(2) and P2X(1) was decreased whereas P2Y(6) expression was increased; (4) in femoral artery, Up(4)A-, UTP-, and UDP-induced contractions were increased, but expression of P2Y(2), P2Y(6) and P2X(1) was unchanged. The α,β-methylene ATP-induced contraction was bell-shaped and the maximal contraction was reached at a lower concentration in basilar and mesenteric arteries from Uni rats, compared to arteries from DOCA-salt rats. These results suggest that Up(4)A-induced contraction is heterogenously affected among various vascular beds in arterial hypertension. P2Y receptor activation may contribute to enhancement of Up(4)A-induced contraction in basilar and femoral arteries. These changes in vascular reactivity to Up(4)A may be adaptive to the vascular alterations produced by hypertension.

Dual signaling pathways of arterial constriction by extracellular uridine 5'-triphosphate in the rat

We investigated actions of uridine 5'-triphosphate (UTP) in rat aorta, cerebral and mesenteric arteries, and their single myocytes. UTP (≥10 µM) elicited an inward-rectifying current strongly reminiscent of activation of P2X(1) receptor, and a similar current was also induced by α,β-methylene adenosine 5'-triphosphate (ATP) (≥100 nM). UTP desensitized α,β-methylene ATP-evoked current, and vice versa. The UTP-activated current was insensitive to G-protein modulators, TRPC3 inhibitors, or TRPC3 antibody, but was sensitive to P2-receptor inhibitors or P2X(1)-receptor antibody. Both UTP (1 mM) and α,β-methylene ATP (10 µM) elicited similar conductance single channel activities. UTP (≥10 µM) provoked a dose-dependent contraction of de-endothelialized aortic ring preparation consisting of phasic and tonic components. Removal of extracellular Ca(2+) or bath-applied 2',3'-O-(2,4,6-trinitrophenyl)-ATP (TNP-ATP) (30 µM) or nifedipine (10 µM) completely inhibited the phasic contraction while only partially reducing the tonic one. The tonic contraction was almost completely abolished by additional application of thapsigargin (2 µM). Similar biphasic rises in [Ca(2+)](i) were also evoked by UTP in rat aortic myocytes. In contrast to the low expression of TRPC3, significant expression of P2X(1) receptor was detected in all arteries by RT-PCR and immunoblotting, and its localization was limited to plasma membrane of myocytes as indicated by immunohistochemistry. These results suggest that UTP dually activates P2X(1)-like and P2Y receptors, but not TRPC3.

Effects of a highly palatable diet on lipid and glucose parameters, nitric oxide, and ectonucleotidases activity

Obesity has reached epidemic proportions worldwide and is stimulated by the ready availability of food rich in fat and sugar (highly palatable diet). This type of diet increases the risks of obesity-associated pathologies, such as insulin resistance and cardiovascular disease. Nitric oxide, a potent endogenous vasodilator, is decreased in these pathologies, mostly as a result of insulin resistance. Ectonucleotidases are ecto and soluble enzymes that regulate the availability of the nucleotides ATP, ADP, and AMP and the nucleoside adenosine in the vascular system, thereby affecting vasoconstriction, vasodilatation, and platelet aggregation homeostasis. The aim of this study was to evaluate the effects of a highly palatable diet on serum lipid and glucose parameters, nitric oxide, and ectonucleotidase activity. Forty male Wistar rats were fed 1 of 2 diets for either 45 days or 4 months: standard chow (SC, n = 10) or a highly palatable diet enriched with sucrose (HP, n = 10). Body mass, visceral fat mass, glucose tolerance, cholesterol (total, high-density lipoprotein (HDL) and non-HDL), serum triacylglycerol, liver triacylglycerol, and free glycerol were increased in the HP group after 45 days and after 4 months, whereas insulin levels were not different between the groups at either time. Furthermore, levels of nitric oxide metabolites and ATP, ADP, and AMP hydrolysis were significantly lower in the HP group (p < 0.05) after 4 months. In conclusion, the consumption of the HP diet for 4 months induced overall corporal and metabolic changes, and decreased nitric oxide metabolites and ectonucleotidase activity, thereby promoting an appropriate environment for the development of cardiovascular diseases, without apparent changes in insulin levels.

G protein-coupled receptor kinase 2 and arrestin2 regulate arterial smooth muscle P2Y-purinoceptor signalling

AIMS

prolonged P2Y-receptor signalling can cause vasoconstriction leading to hypertension, vascular smooth muscle hypertrophy, and hyperplasia. G protein-coupled receptor signalling is negatively regulated by G protein-coupled receptor kinases (GRKs) and arrestin proteins, preventing prolonged or inappropriate signalling. This study investigates whether GRKs and arrestins regulate uridine 5'-triphosphate (UTP)-stimulated contractile signalling in adult Wistar rat mesenteric arterial smooth muscle cells (MSMCs).

METHODS AND RESULTS

mesenteric arteries contracted in response to UTP challenge: When an EC(50) UTP concentration (30 µM, 5 min) was added 5 min before (R(1)) and after (R(2)) the addition of a maximal UTP concentration (R(max): 100 µM, 5 min), R(2) responses were decreased relative to R(1), indicating desensitization. UTP-induced P2Y-receptor desensitization of phospholipase C signalling was studied in isolated MSMCs transfected with an inositol 1,4,5-trisphosphate biosensor and/or loaded with Ca(2+)-sensitive dyes. A similar protocol (R(1)/R(2) = 10 µM; R(max) = 100 µM, applied for 30 s) revealed markedly reduced R(2) when compared with R(1) responses. MSMCs were transfected with dominant-negative GRKs or siRNAs targeting specific GRK/arrestins to probe their respective roles in P2Y-receptor desensitization. GRK2 inhibition, but not GRK3, GRK5, or GRK6, attenuated P2Y-receptor desensitization. siRNA-mediated knockdown of arrestin2 attenuated UTP-stimulated P2Y-receptor desensitization, whereas arrestin3 depletion did not. Specific siRNA knockdown of the P2Y(2)-receptor almost completely abolished UTP-stimulated IP(3)/Ca(2+) signalling, strongly suggesting that our study is specifically characterizing this purinoceptor subtype.

CONCLUSION

these new data highlight roles of GRK2 and arrestin2 as important regulators of UTP-stimulated P2Y(2)-receptor responsiveness in resistance arteries, emphasizing their potential importance in regulating vasoconstrictor signalling pathways implicated in vascular disease.

Assessment and characterization of purinergic contractions and relaxations in the rat urinary bladder

The aim of the present study was to assess the purinoceptor functional responses of the urinary bladder by using isolated rat urinary bladder strip preparations. ATP elicited a transient bladder contraction followed by a sustained relaxation and ADP, UDP and UTP generated predominantly potent relaxations (relaxatory potencies: ADP = ATP > UDP = UTP). The ATP contractions were desensitized with the P2X(1/3) purinoceptor agonist/desensitizer alpha,beta-meATP and reduced by the P2 purinoceptor antagonist PPADS but unaffected by the P2 purinoceptor antagonist suramin. Electrical field stimulation (1-60 Hz) evoked frequency-dependent bladder contractions that were decreased by incubation with alpha,beta-meATP but not further decreased by PPADS. Suramin antagonized relaxations generated by UDP but not those by ADP, ATP or UTP. PPADS antagonized and tended to antagonize UTP and UDP relaxations, respectively, but did neither affect ADP nor ATP relaxations. ADP relaxations were insensitive to the P2Y(1) purinoceptor antagonist MRS 2179 and the ATP-sensitive potassium channel antagonist glibenclamide. The ATP relaxations were inhibited by the P1 purinoceptor antagonist 8-p-sulfophenyltheophylline but unaffected by the A2A adenosine receptor antagonist 8-(3-chlorostyryl)caffeine and glibenclamide. Adenosine evoked relaxations that were antagonized by the A2B adenosine receptor antagonist PSB 1115. Thus, in the rat urinary bladder purinergic contractions are elicited predominantly by stimulation of the P2X(1) purinoceptors, while UDP/UTP-sensitive P2Y purinoceptor(s) and P1 purinoceptors of the A2B adenosine receptor subtype are involved in bladder relaxation.

NTPDase1 (CD39) controls nucleotide-dependent vasoconstriction in mouse

AIMS

Extracellular nucleotides are vasoactive molecules. The concentrations of these molecules are regulated by ectonucleotidases. In this study, we investigated the role of the blood vessel ectonucleotidase NTPDase1, in the vasoconstrictor effect of nucleotides using Entpd1(-/-) mice.

METHODS AND RESULTS

Immunofluorescence, enzyme histochemistry, and HPLC analysis were used to evaluate both NTPDase expression and activity in arteries and isolated vascular smooth muscle cells (VSMCs). Vascular reactivity was evaluated in vitro and mean arterial blood pressure was recorded in anesthetized mice after nucleotide i.v. infusion. Expression of nucleotide receptors in VSMCs was determined by RT-PCR. Entpd1(-/-) mice displayed a dramatic deficit of nucleotidase activity in blood vessel wall in situ and in VSMCs in comparison to control mice. In aortic rings from Entpd1(-/-) mice, UDP and UTP induced a potent and long-lasting constriction contrasting with the weak response obtained in wild-type rings. This constriction occurred through activation of P2Y(6) receptor and was independent of other uracil nucleotide-responding receptors (P2Y(2) and P2Y(4)). UDP infusion in vivo increased blood pressure and this effect was potentiated in Entpd1(-/-) mice. In addition, pressurized mesenteric arteries from Entpd1(-/-) mice displayed an enhanced myogenic response, consistent with higher local concentrations of endogenously released nucleotides. This effect was inhibited by the P2 receptor antagonist RB-2.

CONCLUSION

NTPDase1 is the major enzyme regulating nucleotide metabolism at the surface of VSMCs and thus contributes to the local regulation of vascular tone by nucleotides.

Agonists and antagonists for P2 receptors

Recent work has identified nucleotide agonists selective for P2Y1, P2Y2 and P2Y6 receptors and nucleotide antagonists selective for P2Y1, P2Y12 and P2X1 receptors. Selective non-nucleotide antagonists have been reported for P2Y1, P2Y2, P2Y6, P2Y12, P2Y13, P2X(2/3)/P2X3 and P2X7 receptors. For example, the dinucleotide INS 37217 (Up4dC) potently activates the P2Y2 receptor, and the non-nucleotide antagonist A-317491 is selective for P2X(2/3)/P2X3 receptors. Nucleotide analogues in which the ribose moiety is substituted by a variety of novel ring systems, including conformationally locked moieties, have been synthesized as ligands for P2Y receptors. The focus on conformational factors of the ribose-like moiety allows the inclusion of general modifications that lead to enhanced potency and selectivity. At P2Y1,2,4,11 receptors, there is a preference for the North conformation as indicated with (N)-methanocarba analogues. The P2Y1 antagonist MRS2500 inhibited ADP-induced human platelet aggregation with an IC50 of 0.95 nM. MRS2365, an (N)-methanocarba analogue of 2-MeSADP, displayed potency (EC50) of 0.4nM at the P2Y1 receptor, with >10000-fold selectivity in comparison to P2Y12 and P2Y13 receptors. At P2Y6 receptors there is a dramatic preference for the South conformation. Three-dimensional structures of P2Y receptors have been deduced from structure activity relationships (SAR), mutagenesis and modelling studies. Detailed three-dimensional structures of P2X receptors have not yet been proposed.

Purinergic receptors in the splanchnic circulation

There is considerable evidence that purines are vasoactive molecules involved in the regulation of blood flow. Adenosine is a well known vasodilator that also acts as a modulator of the response to other vasoactive substances. Adenosine exerts its effects by interacting with adenosine receptors. These are metabotropic G-protein coupled receptors and include four subtypes, A(1), A(2A), A(2B) and A(3). Adenosine triphosphate (ATP) is a co-transmitter in vascular neuroeffector junctions and is known to activate two distinct types of P2 receptors, P2X (ionotropic) and P2Y (metabotropic). ATP can exert either vasoconstrictive or vasorelaxant effects, depending on the P2 receptor subtype involved. Splanchnic vascular beds are of particular interest, as they receive a large fraction of the cardiac output. This review focus on purinergic receptors role in the splanchnic vasomotor control. Here, we give an overview on the distribution and diversity of effects of purinergic receptors in splanchnic vessels. Pre- and post-junctional receptormediated responses are summarized. Attention is also given to the interactions between purinergic receptors and other receptors in the splanchnic circulation.

Uridine diphosphate (UDP) stimulates insulin secretion by activation of P2Y6 receptors

We examined the transcriptional expression and functional effects of receptors for the extracellular pyrimidines uridine triphosphate (UTP) and uridine diphosphate (UDP), on insulin and glucagon secretion in isolated mouse pancreatic islets and purified beta-cells. Using real-time PCR, the UDP receptor P2Y(6) was found to be highly expressed in both whole islets and beta-cells purified by repeated counter-flow elutriation, whereas no mRNA expression for UTP receptors P2Y(4) and P2Y(2) could be detected. Functional in vitro experiments revealed that the P2Y(6) agonist UDPbetaS dose-dependently enhanced insulin and glucagon release during short-term incubation (1h), while P2Y(6) activation during a longer period (24h), selectively increased insulin release, especially at high glucose levels. The corresponding EC(50) value for UDPbetaS ranged from 3.2 x 10(-8)M to 1.6 x 10(-8)M for both glucose concentrations. The P2Y(6) antagonist MRS2578 inhibited the effects of UDPbetaS, supporting a P2Y(6) specific effect. In addition to negative RT-PCR results, the lack of response to UTPgammaS a selective P2Y(2/4) agonist further rule out the involvement of P2Y(2/4) receptors in the islet hormone release. Our results suggest a modulatory role for UDP via a functional active P2Y(6) receptor in the regulation of islet hormone release.

P2 receptors in cardiovascular regulation and disease

The role of ATP as an extracellular signalling molecule is now well established and evidence is accumulating that ATP and other nucleotides (ADP, UTP and UDP) play important roles in cardiovascular physiology and pathophysiology, acting via P2X (ion channel) and P2Y (G protein-coupled) receptors. In this article we consider the dual role of ATP in regulation of vascular tone, released as a cotransmitter from sympathetic nerves or released in the vascular lumen in response to changes in blood flow and hypoxia. Further, purinergic long-term trophic and inflammatory signalling is described in cell proliferation, differentiation, migration and death in angiogenesis, vascular remodelling, restenosis and atherosclerosis. The effects on haemostasis and cardiac regulation is reviewed. The involvement of ATP in vascular diseases such as thrombosis, hypertension and diabetes will also be discussed, as well as various heart conditions. The purinergic system may be of similar importance as the sympathetic and renin-angiotensin-aldosterone systems in cardiovascular regulation and pathophysiology. The extracellular nucleotides and their cardiovascular P2 receptors are now entering the phase of clinical development.

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.

Molecular modeling of the human P2Y2 receptor and design of a selective agonist, 2'-amino-2'-deoxy-2-thiouridine 5'-triphosphate

A rhodopsin-based homology model of the nucleotide-activated human P2Y2 receptor, including loops, termini, and phospholipids, was optimized with the Monte Carlo multiple minimum conformational search routine. Docked uridine 5'-triphosphate (UTP) formed a nucleobase pi-pi complex with conserved Phe3.32. Selectivity-enhancing 2'-amino-2'-deoxy substitution interacted through pi-hydrogen-bonding with aromatic Phe6.51 and Tyr3.33. A "sequential ligand composition" approach for docking the flexible dinucleotide agonist Up4U demonstrated a shift of conserved cationic Arg3.29 from the UTP gamma position to the delta position of Up4U and Up4 ribose. Synthesized nucleotides were tested as agonists at human P2Y receptors expressed in 1321N1 astrocytoma cells. 2'-Amino and 2-thio modifications were synergized to enhance potency and selectivity; compound 8 (EC50 = 8 nM) was 300-fold P2Y2-selective versus P2Y4. 2'-Amine acetylation reduced potency, and trifluoroacetylation produced intermediate potency. 5-Amino nucleobase substitution did not enhance P2Y2 potency through a predicted hydrophilic interaction possibly because of destabilization of the receptor-favored Northern conformation of ribose. This detailed view of P2Y2 receptor recognition suggests mutations for model validation.

P2 receptors in atherosclerosis and postangioplasty restenosis

Atherosclerosis is an immunoinflammatory process that involves complex interactions between the vessel wall and blood components and is thought to be initiated by endothelial dysfunction [Ross (Nature 362:801–09, 1993); Fuster et al. (N Engl J Med 326:242–50, 1992); Davies and Woolf (Br Heart J 69:S3–S11, 1993)]. Extracellular nucleotides that are released from a variety of arterial and blood cells [Di Virgilio and Solini (Br J Pharmacol 135:831–42, 2002)] can bind to P2 receptors and modulate proliferation and migration of smooth muscle cells (SMC), which are known to be involved in intimal hyperplasia that accompanies atherosclerosis and postangioplasty restenosis [Lafont et al. (Circ Res 76:996–002, 1995)]. In addition, P2 receptors mediate many other functions including platelet aggregation, leukocyte adherence, and arterial vasomotricity. A direct pathological role of P2 receptors is reinforced by recent evidence showing that upregulation and activation of P2Y₂ receptors in rabbit arteries mediates intimal hyperplasia [Seye et al. (Circulation 106:2720–726, 2002)]. In addition, upregulation of functional P2Y receptors also has been demonstrated in the basilar artery of the rat double-hemorrhage model [Carpenter et al. (Stroke 32:516–22, 2001)] and in coronary artery of diabetic dyslipidemic pigs [Hill et al. (J Vasc Res 38:432–43, 2001)]. It has been proposed that upregulation of P2Y receptors may be a potential diagnostic indicator for the early stages of atherosclerosis [Elmaleh et al. (Proc Natl Acad Sci U S A 95:691–95, 1998)]. Therefore, particular effort must be made to understand the consequences of nucleotide release from cells in the cardiovascular system and the subsequent effects of P2 nucleotide receptor activation in blood vessels, which may reveal novel therapeutic strategies for atherosclerosis and restenosis after angioplasty.

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

BACKGROUND AND PURPOSE

The uracil nucleotides UDP and UTP have been reported to activate P2Y2, P2Y4 and P2Y6 receptors to cause vasoconstriction. We have performed a comparative analysis of these receptors in endothelium-denuded smooth muscle from porcine isolated coronary and ear arteries, using pharmacological and molecular tools.

EXPERIMENTAL APPROACH

Tissue segments were used to construct non-cumulative concentration response curves for UTP and UDP, in the absence and presence of the P2 receptor antagonists PPADS or suramin. RT-PCR and immunoblot analyses were employed to define gene expression and immunoreactivity for P2Y2, P2Y4 and P2Y6 receptors.

KEY RESULTS

In the coronary artery, UTP-evoked contractile responses were reduced in the presence of suramin, but not PPADS, while the smaller responses to UDP were unaffected by either antagonist. In the ear artery, contractile responses to UDP were much smaller than those to UTP; responses to UTP were inhibited by both PPADS and suramin. RT-PCR suggested predominant expression of P2Y2 receptors in the coronary artery, while P2Y4 and P2Y6 receptor gene expression appeared equivalent in both tissues. Immunoblot analyses provided evidence for P2Y6 receptors in both tissues, with equivocal evidence of P2Y2 and P2Y4 receptor immunoreactivities.

CONCLUSIONS AND IMPLICATIONS

We conclude that UTP-evoked contraction of porcine coronary artery smooth muscle appears to be predominantly P2Y2-mediated, while the ear artery appears to express a uracil nucleotide-sensitive P2 receptor(s) which fails to fit readily into the current classification.

International Union of Pharmacology LVIII: update on the P2Y G protein-coupled nucleotide receptors: from molecular mechanisms and pathophysiology to therapy

There have been many advances in our knowledge about different aspects of P2Y receptor signaling since the last review published by our International Union of Pharmacology subcommittee. More receptor subtypes have been cloned and characterized and most orphan receptors de-orphanized, so that it is now possible to provide a basis for a future subdivision of P2Y receptor subtypes. More is known about the functional elements of the P2Y receptor molecules and the signaling pathways involved, including interactions with ion channels. There have been substantial developments in the design of selective agonists and antagonists to some of the P2Y receptor subtypes. There are new findings about the mechanisms underlying nucleotide release and ectoenzymatic nucleotide breakdown. Interactions between P2Y receptors and receptors to other signaling molecules have been explored as well as P2Y-mediated control of gene transcription. The distribution and roles of P2Y receptor subtypes in many different cell types are better understood and P2Y receptor-related compounds are being explored for therapeutic purposes. These and other advances are discussed in the present review.

P2 receptors in atherosclerosis and postangioplasty restenosis

Atherosclerosis is an immunoinflammatory process that involves complex interactions between the vessel wall and blood components and is thought to be initiated by endothelial dysfunction [1-3]. Extracellular nucleotides that are released from a variety of arterial and blood cells [4] can bind to P2 receptors and modulate proliferation and migration of smooth muscle cells (SMC), which is known to be involved in intimal hyperplasia that accompanies atherosclerosis and postangioplasty restenosis [5]. In addition, P2 receptors mediate many other functions, including platelet aggregation, leukocyte adherence, and arterial vasomotoricity. A direct pathological role of P2 receptors is reinforced by recent evidence showing that up-regulation and activation of P2Y(2) receptors in rabbit arteries mediates intimal hyperplasia [6]. In addition, up-regulation of functional P2Y receptors also has been demonstrated in the basilar artery of the rat double-hemorrhage model [7] and in coronary arteries of diabetic dyslipidemic pigs [8]. It has been proposed that up-regulation of P2Y receptors may be a potential diagnostic indicator for the early stages of atherosclerosis [9]. Therefore, particular effort must be made to understand the consequences of nucleotide release from cells in the cardiovascular system and the subsequent effects of P2 nucleotide receptor activation in blood vessels, which may reveal novel therapeutic strategies for atherosclerosis and restenosis after angioplasty.

Positive inotropic effects by uridine triphosphate (UTP) and uridine diphosphate (UDP) via P2Y2 and P2Y6 receptors on cardiomyocytes and release of UTP in man during myocardial infarction

The aim of this study was to examine a possible role for extracellular pyrimidines as inotropic factors for the heart. First, nucleotide plasma levels were measured to evaluate whether UTP is released in patients with coronary heart disease. Then, inotropic effects of pyrimidines were examined in isolated mouse cardiomyocytes. Finally, expression of pyrimidine-selective receptors (a subgroup of the P2 receptors) was studied in human and mouse heart, using real time polymerase chain reaction, Western blot, and immunohistochemistry. Venous plasma levels of UTP were increased (57%) in patients with myocardial infarction. In electrically stimulated cardiomyocytes the stable P2Y(2/4) agonist UTPgammaS increased contraction by 52%, similar to beta1-adrenergic stimulation with isoproterenol (65%). The P2Y6-agonist UDPbetaS also increased cardiomyocyte contraction (35%), an effect abolished by the P2Y6-blocker MRS2578. The phospholipase C inhibitor U73122 inhibited both the UDPbetaS and the UTPgammaS-induced inotropic effect, indicating an IP3-mediated effect via P2Y6 receptors. The P2Y14 agonist UDP-glucose was without effect. Quantification of mRNA with real time polymerase chain reaction revealed P2Y2 as the most abundant pyrimidine receptor expressed in cardiomyocytes from man. Presence of P2Y6 receptor mRNA was detected in both species and confirmed at protein level with Western blot and immunohistochemistry in man. In conclusion, UTP levels are increased in humans during myocardial infarction, giving the first evidence for UTP release in man. UTP is a cardiac inotropic factor most likely by activation of P2Y2 receptors in man. For the first time we demonstrate inotropic effects of UDP, mediated by P2Y6 receptors via an IP3-dependent pathway. Thus, the extracellular pyrimidines (UTP and UDP) could be important inotropic factors involved in the development of cardiac disease.

Structure activity and molecular modeling analyses of ribose- and base-modified uridine 5'-triphosphate analogues at the human P2Y2 and P2Y4 receptors

With the long-term goal of developing receptor subtype-selective high affinity agonists for the uracil nucleotide-activated P2Y receptors we have carried out a series of structure activity and molecular modeling studies of the human P2Y2 and P2Y4 receptors. UTP analogues with substitutions in the 2'-position of the ribose moiety retained capacity to activate both P2Y2 and P2Y4 receptors. Certain of these analogues were equieffective for activation of both receptors whereas 2'-amino-2'-deoxy-UTP exhibited higher potency for the P2Y2 receptor and 2'-azido-UTP exhibited higher potency for the P2Y4 receptor. 4-Thio substitution of the uracil base resulted in a UTP analogue with increased potency relative to UTP for activation of both the P2Y2 and P2Y4 receptors. In contrast, 2-thio substitution and halo- or alkyl substitution in the 5-position of the uracil base resulted in molecules that were 3-30-fold more potent at the P2Y2 receptor than P2Y4 receptor. 6-Aza-UTP was a P2Y2 receptor agonist that exhibited no activity at the P2Y4 receptor. Stereoisomers of UTPalphaS and 2'-deoxy-UTPalphaS were more potent at the P2Y2 than P2Y4 receptor, and the R-configuration was favored at both receptors. Molecular docking studies revealed that the binding mode of UTP is similar for both the P2Y2 and P2Y4 receptor binding pockets with the most prominent dissimilarities of the two receptors located in the second transmembrane domain (V90 in the P2Y2 receptor and I92 in the P2Y4 receptor) and the second extracellular loop (T182 in the P2Y2 receptor and L184 in the P2Y4 receptor). In summary, this work reveals substitutions in UTP that differentially affect agonist activity at P2Y2 versus P2Y4 receptors and in combination with molecular modeling studies should lead to chemical synthesis of new receptor subtype-selective drugs.

Characterization of purine receptors in mouse thoracic aorta

The contracting and relaxing effects of purines and UTP were investigated on rings of mouse thoracic aorta in vitro. UTP, ATP gamma S, and alpha-beta-Methyleneadenosine 5'triphosphate contracted rings with and without endothelium. On the contrary, adenosine, AMP, ADP, ATP, and 2-(methylthio)adenosine 5'-diphosphate had no effect on relaxed rings. When rings were tonically contracted by U46619 a thromboxane A2 analogue, ATP, ADP, ATP gamma S, 2-(methylthio)adenosine 5'-diphosphate, and UTP caused endothelium-dependent but not independent relaxations.I conclude that ATP acts on P2Y2 and P2Y1 receptors on the endothelial cells to cause endothelium-dependent relaxation. In this tissue, the relaxing effect of ATP dominates by endothelium-dependent ways when aorta rings are contracted by a stable thromboxane A2 analog. However receptors mediating contraction in response to purines and pyrimidines are present on smooth muscle cells. Indeed, the stimulation of P2Y receptors by UTP as well as the activation of P2X family receptors by ATP gamma S causes a contraction. The potential contractile effect of ATP seems masked by its hydrolysis by ectonucleotidases.

Angiotensin II Receptor mRNA Expression and Vasoconstriction in Human Coronary Arteries: Effects of Heart Failure and Age

Angiotensin II is a potent vasoconstrictor that is implicated in the pathogenesis of hypertension, heart failure and atherosclerosis. In the present study, angiotensin II receptor mRNA expression levels were quantified by real-time polymerase chain reaction and the vasocontractile responses to angiotensin II were characterised by in vitro pharmacology in endothelium-denuded human coronary arteries. Angiotensin II type 1 (AT(1)) and type 2 (AT(2)) receptor mRNA expression levels were significantly down-regulated in arteries from patients with heart failure as compared to controls. The angiotensin II-induced vasoconstriction diminished with increasing age in patients with heart failure (r(2)=0.31, P<0.05). Also, the AT(1) receptor mRNA expression levels decreased with increasing age in patients with heart failure (r(2)=0.74, P<0.05), while no such correlation could be shown in the control group (r(2)=0.04, P=n.s.). The AT(2) receptor mRNA expression levels did not correlate with age in patients with heart failure or controls. In conclusion, the diminished angiotensin II vasoconstriction with age in heart failure patients is most likely due to a lower density of AT(1) receptors and may result from a longer period of exposure to heart failure in older patients.

alpha,beta-MeATP augments the UTP contraction of rabbit basilar artery

The mechanism underlying the interaction between alpha,beta-methyleneadenosine 5'-triphosphate (alpha,beta-MeATP) and uridine 5'-triphosphate (UTP) was investigated using the basilar artery of a rabbit. UTP induced a concentration-dependent contraction, whereas P2X receptor agonists, such as alpha,beta-MeATP and 2-methylthioadenosine 5'-triphosphate (2-MeSATP), did not induce any contraction up to 100 microM. alpha,beta-MeATP augmented the UTP contraction two-fold, immediately and reversibly. This effect was observed with ectonucleotidase inhibition with 1 mM Ni(2+), the removal of extracellular Ca(2+) or Evans blue. The contractile response to adenosine 5'-O-(3-triphosphate) (ATPgammaS), a selective agonist for P2Y(4), was augmented by pretreatment with alpha,beta-MeATP also. ATPgammaS had no additional effect on the UTP contraction fully activated with alpha,beta-MeATP. UTP (100 microM) did not induce an increase in cytosolic Ca(2+) in a rabbit basilar arterial strip; however, in the presence of 1 mM alpha,beta-MeATP, UTP induced a significant increase in cytosolic Ca(2+). These results suggest that alpha,beta-MeATP facilitates the activation by UTP of the P2Y receptor (P2Y(4)) of the rabbit basilar artery through mechanisms other than nucleotidase inhibition, and that it does not do so via a P2X receptor.

Cloning, Up-Regulation, and Mitogenic Role of Porcine P2Y2 Receptor in Coronary Artery Smooth Muscle Cells

Previous work has shown up-regulation of a UTP-sensitive P2Y receptor in porcine coronary smooth muscle cells (CSMC) of organ-cultured arteries. However, the molecular identity and functional role of this putative receptor remained undefined. Here we report the cloning of the cDNA for this receptor that encodes an open reading frame for a protein of 373 amino acids with the highest homology to the human P2Y(2) receptor (84%). Heterologous expression of this receptor in 1321N1 cells revealed a novel pharmacology in that UTP and ITP were full agonists and UTP was more potent and efficacious than ATP for increasing intracellular [Ca(2+)] and extracellular signal-regulated kinase phosphorylation. Stimulation of subcultured CSMC with UTP, ITP, or ATP induced a concentration-dependent increase in cellular DNA content, protein synthesis, cell number, and proliferating cell nuclear antigen expression, indicating a mitogenic role for P2Y(2) receptors. This was supported by the finding that the treatment of CSMC with antisense oligonucleotides to the cloned cDNA sequence significantly inhibited UTP- and ATP-induced DNA and protein synthesis. In addition, reverse transcription-polymerase chain reaction analysis showed that P2Y(2) receptor mRNA was dramatically increased in cells of organ-cultured arteries compared with freshly harvested arteries, whereas the P2Y(6) receptor mRNA level was unchanged, and the P2Y(4) receptor mRNA was undetectable. This P2Y(2) subtype-specific up-regulation was confirmed in cells of coronary arteries stented in vivo. In conclusion, we have cloned the porcine P2Y(2) receptor with novel pharmacology and demonstrated that this receptor is up-regulated in CSMC of in vitro organ cultures or in vivo stented coronary arteries to mediate the mitogenic effects of nucleotides.

Effects of a topical enamel matrix derivative on skin wound healing

Enamel matrix derivative, obtained from developing porcine teeth, is composed mainly of amelogenin proteins and used topically in periodontal surgery for advanced periodontitis to regenerate lost connective tissues. The primary objective of this study was to investigate the effects of enamel matrix derivative on skin wound healing. Secondly, in vitro effects of enamel matrix derivative on dermal fibroblasts and microvascular endothelial cells were examined. Full-thickness, circular 2-cm skin wounds in white 16-week-old rabbits were treated thrice weekly with enamel matrix derivative (30 mg/ml) in the vehicle propylene glycol alginate or with vehicle alone. Enamel matrix derivative treatment increased the amount of granulation tissue and accelerated time to complete epithelialization by 3 days (p < 0.001) compared to vehicle treatment. In cultured fibroblasts, vascular endothelial growth factor levels in conditioned media were increased more than fivefold (p < 0.001) with enamel matrix derivative treatment (0.1mg/ml) over control, measured by specific enzyme-linked immunosorbent assay. Enamel matrix derivative also increased release of matrix metalloproteinase-2 more than threefold from fibroblasts (p < 0.001) and from endothelial cells (p < 0.001). Thus, enamel matrix derivative significantly accelerated wound closure in rabbits, possibly by increasing levels of growth factors and proteinases important for granulation tissue formation and remodeling.

Cellular Distribution and Functions of P2 Receptor Subtypes in Different Systems

This review is aimed at providing readers with a comprehensive reference article about the distribution and function of P2 receptors in all the organs, tissues, and cells in the body. Each section provides an account of the early history of purinergic signaling in the organ?cell up to 1994, then summarizes subsequent evidence for the presence of P2X and P2Y receptor subtype mRNA and proteins as well as functional data, all fully referenced. A section is included describing the plasticity of expression of P2 receptors during development and aging as well as in various pathophysiological conditions. Finally, there is some discussion of possible future developments in the purinergic signaling field.

Molecular recognition at purine and pyrimidine nucleotide (P2) receptors

In comparison to other classes of cell surface receptors, the medicinal chemistry at P2X (ligand-gated ion channels) and P2Y (G protein-coupled) nucleotide receptors has been relatively slow to develop. Recent effort to design selective agonists and antagonists based on a combination of library screening, empirical modification of known ligands, and rational design have led to the introduction of potent antagonists of the P2X(1) (derivatives of pyridoxal phosphates and suramin), P2X(3)(A-317491), P2X(7) (derivatives of the isoquinoline KN-62), P2Y(1)(nucleotide analogues MRS 2179 and MRS 2279), P2Y(2)(thiouracil derivatives such as AR-C126313), and P2Y(12)(nucleotide/nucleoside analogues AR-C69931X and AZD6140) receptors. A variety of native agonist ligands (ATP, ADP, UTP, UDP, and UDP-glucose) are currently the subject of structural modification efforts to improve selectivity. MRS2365 is a selective agonist for P2Y(1)receptors. The dinucleotide INS 37217 potently activates the P2Y(2)receptor. UTP-gamma-S and UDP-beta-S are selective agonists for P2Y(2)/P2Y(4)and P2Y(6)receptors, respectively. The current knowledge of the structures of P2X and P2Y receptors, is derived mainly from mutagenesis studies. Site-directed mutagenesis has shown that ligand recognition in the human P2Y(1)receptor involves individual residues of both the TMs (3, 5, 6, and 7), as well as EL 2 and 3. The binding of the negatively-charged phosphate moiety is dependent on positively charged lysine and arginine residues near the exofacial side of TMs 3 and 7.

Ischemic heart disease induce upregulation of endothelin receptor mRNA in human coronary arteries

Endothelin has been implicated in the pathogenesis of ischemic heart disease and congestive heart failure. The aims were to quantify endothelin type A (ETA) and type B (ETB) receptor mRNA levels in human coronary arteries from patients with ischemic heart disease, congestive heart failure and controls using real-time polymerase chain reaction (real-time PCR). In addition, the suitability of organ culture as a model mimicking endothelin receptor changes in cardiovascular disease was evaluated by in vitro pharmacology and real-time PCR. Endothelin ETA and ETB receptor mRNA levels were significantly higher in arteries from patients with ischemic heart disease (0.23+/-0.04 and 0.35+/-0.06) as compared to congestive heart failure (0.09+/-0.02 and 0.07+/-0.01) and controls (0.08+/-0.02 and 0.08+/-0.01). After organ culture, the endothelin ETB receptor mRNA levels were elevated, and the sarafotoxin 6c-induced vasoconstriction was more efficacious. Increased endothelin receptor activity may contribute to the increased vascular tone and development of atherosclerotic disease in ischemic heart disease in man.

ATP and UTP responses of cultured rat aortic smooth muscle cells revisited: dominance of P2Y2 receptors

1. It has previously been shown that ATP and UTP stimulate P2Y receptors in vascular smooth muscle cells (VSMCs), but the nature of these receptors, in particular the contribution of P2Y2 and P2Y4 subtypes, has not been firmly established. Here we undertake a further pharmacological analysis of [3H]inositol polyphosphate responses to nucleotides in cultured rat VSMCs. 2. ATP generated a response that was partial compared to UTP, as reported earlier. 3. In the presence of a creatine phosphokinase (CPK) system for regenerating nucleoside triphosphates, the response to ATP was increased, the response to UTP was unchanged, and the difference between UTP and ATP concentration-response curves disappeared. Chromatographic analysis showed that ATP was degraded slightly faster than UTP. 4. The response to UDP was always smaller than that to UTP, but with a shallow slope and a high potency component. In the presence of hexokinase (which prevents the accumulation of ATP/UTP from ADP/UDP), the maximum response to UDP was reduced and the high-potency component of the curve was retained. By contrast, the response to ADP was weaker throughout in the presence of hexokinase. 5. ATP gamma S was an effective agonist with a similar EC50 to UTP, but with a lower maximum. ITP was a weak agonist compared with UTP. 6. Suramin was an effective antagonist of the response to UTP (pA2=4.48), but not when ATP was the agonist. However, suramin was an effective antagonist (pA2=4.45) when stimulation with ATP was in the presence of the CPK regenerating system. 7. Taken together with the results of others, these findings indicate that the response of cultured rat VSMCs to UTP and to ATP is predominantly at the P2Y2 receptor, and that there is also a response to UDP at the P2Y6 receptor.

Contractions in human coronary bypass vessels stimulated by extracellular nucleotides

BACKGROUND

The present study was designed to evaluate the relative contribution of different contractile P2 receptors in human saphenous vein compared with internal mammary artery obtained during coronary artery surgery.

METHODS

The isometric tension in endothelium-denuded isolated vessel segments was recorded in vitro. The P2 receptor mRNA expression was quantified by real-time polymerase chain reaction.

RESULTS

The P2X(1) receptor agonist, alphabeta-MeATP (alphabeta-methylene-adenosine triphosphate), was the most potent vasoconstrictor, with more efficacious contractions in the saphenous vein than in the internal mammary artery. The selective P2Y(6) receptor agonist, UDPbetaS (uridine 5'-O-thiodiphosphate), stimulated more potent contractions in saphenous vein compared with internal mammary artery. Furthermore, UDPbetaS induced long-lasting contractions for more than 2 hours, explained by the low desensitization rate of the P2Y(6) receptor. The ATP-induced vasoconstriction could not be abolished by desensitization of P2X(1) receptors with alphabeta-MeATP, or P2Y(2/4) receptors with UTPgammaS (uridine 5'-O-3-thiotriphosphate), indicating the presence of yet another contractile ATP receptor. Based on quantification with real-time polymerase chain reaction, the P2Y(11) receptor could be responsible for this ATP contraction.

CONCLUSIONS

The P2X(1) and P2Y(6) receptors elicit more prominent contractions in the saphenous vein as compared with the internal mammary artery. These results may present one explanation for the differences in the two conduits. It is possible that selective antagonists of P2X(1) and P2Y(6) receptors could be used to prevent vasospasm and restenosis in the saphenous vein during and after revascularization surgery.

Endothelium-dependent relaxation and endothelial hyperpolarization by P2Y receptor agonists in rat-isolated mesenteric artery

(1) Vasorelaxation and hyperpolarization of endothelial cells by adenosine 5'-[beta-thio]diphosphate (ADPbetaS) and adenosine 5'-[gamma-thio]triphosphate (ATPgammaS) were studied in rat-isolated mesenteric artery. Effects from stimulation of P2X receptors were avoided by desensitization with alpha,beta-methylene adenosine triphosphate. (2) ADPbetaS caused concentration- and endothelium-dependent relaxations of methoxamine-precontracted small (third generation) and main mesenteric artery. These were inhibited by N(omega)-nitro-L-arginine methyl ester (L-NAME) or a combination of apamin plus charybdotoxin (inhibitors of Ca(2+)-activated K(+) channels); L-NAME, apamin and charybdotoxin applied together abolished the response. (3) ATPgammaS induced limited relaxation (35% of methoxamine-induced tone at 10 micro M) of small mesenteric artery, which was sensitive to L-NAME or endothelium denudation. However, it almost completely relaxed the main mesenteric artery over an extended concentration range (>6 orders of magnitude) in an endothelium-dependent manner. This relaxation was inhibited by either L-NAME or a combination of apamin with charybdotoxin, and abolished by a combination of all the three inhibitors. (4) The P2Y(1) receptor antagonist MRS 2179 (2'-deoxy-N(6)-methyladenosine 3',5'-bisphosphate; 0.3-3 micro M) caused parallel rightward shifts of the concentration/relaxation curve to ADPbetaS (pA(2)=7.1). However, MRS 2179 did not inhibit, but potentiated, relaxant responses to ATPgammaS. MRS 2179 did not affect the contractile responses ATPgammaS in small mesenteric artery; ATPgammaS did not contract the main mesenteric artery. (5) ADPbetaS hyperpolarized the endothelium of the main mesenteric artery in a concentration-dependent manner. This was unaffected by L-NAME but antagonized by MRS 2179. ATPgammaS also hyperpolarized the mesenteric artery endothelium in a concentration-dependent manner but, when ATPgammaS was applied at 10 micro M, its effect was potentiated by MRS 2179 (3 micro M). (6) It is concluded that both relaxation and hyperpolarization to ADPbetaS are mediated by P2Y(1) receptors and that the endothelial hyperpolarization is related to the L-NAME-resistant relaxation. Relaxation to the P2Y(2) agonist ATPgammaS shows regional variation along the mesenteric vasculature. The mechanisms for potentiation of relaxation and hyperpolarization by ATPgammaS are unknown, but may indicate interactions between P2Y receptor subtypes.

P2Y6 nucleotide receptor activates PKC to protect 1321N1 astrocytoma cells against tumor necrosis factor-induced apoptosis

1. We recently reported that the activation by UDP of rat P2Y6 nucleotide receptors expressed in 1321N1 astrocytoma cells protected them from TNFalpha-induced apoptosis by suppressing activation of caspase 3 and 8. This study aims to characterize the involvement of intracellular signaling pathways, including kinases involved in the antiapoptotic effect of UDP. 2. Cell death was induced in 1321N1 astrocytoma cells permanently expressing the rat P2Y6 receptor by exposure to TNFalpha in the presence of cycloheximide. The apoptotic fraction was analyzed using flow cytometry. 3. The activation of P2Y6 receptors by UDP both protected the astrocytes from TNF-alpha induced apoptosis and activated protein kinase C (PKC) isotypes. The phorbol ester PMA also activated PKC and protected the cells from TNFalpha-induced cell death. The alpha- and epsilon-isotypes of PKC were both activated in a persistent fashion upon 5-min exposure to either UDP (10 microM) or the phorbol ester PMA (100 nM). The PKCzeta isotype was markedly activated upon UDP treatment. 4. The addition of PKC inhibitors, GF109203X or Gö6976, partially antagonized the protective effect of UDP and reduced the UDP-induced phosphorylation of extracellular signal-regulated protein kinases (Erk). The inhibitors of Erk, PD98,059 or U0126, antagonized UDP-induced protection. 5. The antiapoptotic protein, Akt, was not affected by P2Y6 receptor activation. Incubation of the astrocytes with calcium modifiers BAPTA-AM or dantrolene, did not affect the UDP-induced protection from apoptosis. 6. The addition of phospholipase C (PLC) inhibitors, D609 or U73122, partially antagonized both UDP-induced protection and PKC activation.

Potent P2Y6 receptor mediated contractions in human cerebral arteries

BACKGROUND

Extracellular nucleotides play an important role in the regulation of vascular tone and may be involved in cerebral vasospasm after subarachnoidal haemorrhage. This study was designed to characterise the contractile P2 receptors in endothelium-denuded human cerebral and omental arteries. The isometric tension of isolated vessel segments was recorded in vitro. P2 receptor mRNA expression was examined by RT-PCR.

RESULTS

In human cerebral arteries, the selective P2Y6 receptor agonist, UDPbetaS was the most potent of all the agonists tested (pEC50 = 6.8 PlusMinus; 0.7). The agonist potency; UDPbetaS > alphabeta-MeATP > UTPgammaS > ATPgammaS > ADPbetaS = 0, indicated the presence of contractile P2X1 P2Y2, P2Y4 and P2Y6, but not P2Y1 receptors, in human cerebral arteries. In human omental arteries, UDPbetaS was inactive. The agonist potency; alphabeta-MeATP > ATPgammaS = UTPgammaS > ADPbetaS = UDPbetaS = 0, indicated the presence of contractile P2X1, and P2Y2 receptors, but not P2Y1 or P2Y6 receptors, in human omental arteries. RT-PCR analysis of endothelium-denuded human cerebral and omental arteries demonstrated P2X1, P2Y1, P2Y2 and P2Y6 receptor mRNA expression. There were no bands for the P2Y4 receptor mRNA in the omental arteries, while barely detectable in the cerebral arteries.

CONCLUSIONS

P2Y6 receptors play a prominent role in mediating contraction of human cerebral arteries. Conversely, no such effect can be observed in human omental arteries and previous results confirm the absence of P2Y6 receptors in human coronary arteries. The P2Y6 receptor might be a suitable target for the treatment of cerebral vasospasm.

Extracellular nucleotides induce vasodilatation in human arteries via prostaglandins, nitric oxide and endothelium-derived hyperpolarising factor

1. The present study was aimed at examining P2 receptor-mediated vasodilatation in human vessels. The isometric tension was recorded in isolated segments of the human left internal mammary artery branches precontracted with 1 microM noradrenaline. 2. Endothelial denudation abolished the dilator responses. 3. The selective P2Y(1) agonist, 2-MeSADP, induced a potent vasodilatation (pEC(50)=6.9+/-0.1). The P2Y(1) antagonist of 10 microM, MRS 2216, shifted the 2-MeSADP concentration-response curve 1.1 log units to the right. The combined P2Y(1) and P2X agonist, 2-MeSATP, stimulated a dilatation with a potency similar to that of 2-MeSADP. Furthermore, MRS 2216 had a similar antagonistic effect on both 2-MeSATP and 2-MeSADP indicating that P2X receptors do not mediate vasodilatation. 4. Both the P2Y(2/4) agonist, UTPgammaS and the P2Y(6) agonist, UDPbetaS, stimulated potent dilatations (pEC(50)=7.8+/-0.4 for UTPgammaS and 8.4+/-0.2 for UDPbetaS). 5. The 2-MeSADP-induced nitric oxide (NO)-mediated dilatation was studied in the presence of 10 micro M indomethacin, 50 nM charybdotoxin and 1 microM apamin. The involvement of the endothelium-derived hyperpolarising factor (EDHF) was investigated in the presence of 0.1 mM L-NOARG and indomethacin. The involvement of prostaglandins was investigated in the presence of L-NOARG, charybdotoxin and apamin. Both NO, EDHF and prostaglandins mediated 2-MeSADP dilatation with similar efficacy (E(max)=25+/-5% for NO, 25+/-6% for EDHF and 27+/-5% for prostaglandins). 6. In conclusion, extracellular nucleotides induce endothelium-derived vasodilatation in human vessels by stimulating P2Y(1), P2Y(2/4) and P2Y(6) receptors, while P2X receptors are not involved. Endothelial P2Y receptors mediate dilatation by release of EDHF, NO and prostaglandins.

Endothelin receptors in endothelium-denuded human coronary artery bypass grafts and coronary arteries

BACKGROUND

Coronary artery bypass graft (CABG) surgery is hampered by deleterious vasospasm in the vessel wall, especially in vein grafts. Endothelin (ET) is a strong vasoconstrictor that can be observed in increasing concentrations during CABG surgery.

METHODS

Endothelin-induced vasoconstriction was evaluated in isolated, endothelium-denuded vessel segments of the human saphenous vein (SV), left internal mammary artery (LIMA), and coronary arteries. The ET(A) and ET(B) receptor mRNA levels were quantified by real-time polymerase chain reaction (PCR) analysis.

RESULTS

The ET(A) and ET(B) receptor mRNA levels were significantly higher in the SV than in the LIMA and the coronary arteries. ET-1 induced a more efficacious contraction in the SV and LIMA as compared with in the coronary arteries. The ET(B) receptor agonist, Sarafotoxin 6c (S6c) stimulated constriction of the LIMA and SV, while inactive in the coronary arteries. The concentration-response curve for S6c was biphasic, suggesting activation of ET(A) receptors at high concentrations as this response could be inhibited by FR139317 (10 micromol/L), and ET(B) at low concentrations as this response could be inhibited by BQ788 (0.1 micromol/L).

CONCLUSIONS

Endothelin-induced vasoconstriction is mediated by ET(A) receptors alone in coronary arteries, while a combination of ET(A) and ET(B) receptors are of importance in SV and LIMA. Expression of contractile ET(B) receptors may be a pharmacologic disadvantage that contributes to the vasospasm during CABG surgery. The lower levels of ET(A) and ET(B) receptor mRNA in the LIMA and coronary arteries as compared with in the SV may provide one explanation for the better long- and short-term patency of LIMA as compared with SV grafts.

The stable pyrimidines UDPbetaS and UTPgammaS discriminate between contractile cerebrovascular P2 receptors

Extracellular nucleotides were used to characterise the contractile P2 receptors in the rat basilar artery. The isometric tension was recorded in vitro and receptor mRNA expression was examined by reverse transcriptase polymerase chain reaction (RT-PCR) after endothelium-denudation. Transient vasoconstriction was evoked by alphabeta-methylene-adenosine triphosphate (alphabeta-MeATP), indicating the presence of P2X(1) receptors. The P2Y receptors were analysed after P2X receptor desensitisation with 10 microM alphabeta-MeATP. Uridine diphosphate (UDP) and uridine triphosphate (UTP) induced sustained contractions of similar magnitude. The stable nucleotide analogue, uridine 5'-O-thiodiphosphate (UDPbetaS), was clearly more potent than uridine 5'-O-3-thiotriphosphate (UTPgammaS), suggesting prominent contractile effects of P2Y(6) receptors. P2Y(2) and P2Y(4) receptors might also be involved in nucleotide responses, since UTPgammaS and adenosine 5'-O-3-thiotriphosphate (ATPgammaS) were of similar potency. The P2Y(1) selective agonists, adenosine 5'-O-thiodiphosphate (ADPbetaS) and 2-methylthioadenosine diphosphate (2-MeSADP) did not induce contractions. RT-PCR analysis demonstrated P2X(1), P2Y(1), P2Y(2) and P2Y(6) receptor mRNA expression, while the P2Y(4) band was weak. In conclusion, extracellular nucleotides induce contractions of cerebral arteries primarily by activation of P2Y(6) receptors on smooth muscle cells, with a lesser contribution of P2Y(2) and P2X(1) receptors. Although mRNA for the P2Y(1) receptor was detected by RT-PCR, it does not mediate contraction.

P2 receptor expression profiles in human vascular smooth muscle and endothelial cells

P2 receptors mediate the actions of the extracellular nucleotides ATP, ADP, UTP, and UDP, regulating several physiologic responses including cardiac function, vascular tone, smooth muscle cell (SMC) proliferation, platelet aggregation, and the release of endothelial factors. P2 receptor characterization has been hampered by the lack of selective antagonists. The aim of the current study was to investigate the mRNA and protein expression of P2X and P2Y receptors in human SMC and in endothelial cells (EC). Smooth muscle cells were obtained from human mammary artery and EC from human umbilical vein. Using real-time PCR, the authors established quantitative mRNA assays. Protein expression was studied using Western blotting with recently developed antibodies. The P2X1 receptor was highly specific for human SMC, while the P2X4 was the highest expressed receptor in EC. The P2Y2 receptor was present in both SMC and EC. UTP-mediated effects in these cells are likely to be mediated by P2Y2 and not P2Y4 receptors since the latter had considerably lower expression. The P2Y6 receptor was expressed in both SMC and EC. The P2Y1 and surprisingly the P2Y11 receptors were the most abundantly expressed P2Y receptors in the endothelium. Overall, Western blotting confirmed the mRNA findings in most aspects, and most interestingly, indicated oligomerization of the P2Y1 receptor that may be important for its function. In conclusion, P2X1, P2Y2, and P2Y6 are the most expressed P2 receptors in SMC and are thus probably mediating the contractile and mitogenic actions of extracellular nucleotides. The P2X4, P2Y11, P2Y1, and P2Y2 are the most expressed P2 receptors in EC, and are most likely mediating release of nitric oxide, endothelium-dependent hyperpolarizing factor (EDHF), and t-PA induced by extracellular nucleotides. These findings will help to direct future cardiovascular drug development against the large P2 receptor family.