Phenotype changes of the vascular smooth muscle cell regulate P2 receptor expression as measured by quantitative RT-PCR

Alterations of the Ca2+ clearing mechanisms by type 2 diabetes in aortic smooth muscle cells of Zucker diabetic fatty rat

Type 2 Diabetes Mellitus (T2DM) is a rapidly rising disease with cardiovascular complications constituting the most common cause of death among diabetic patients. Chronic hyperglycemia can induce vascular dysfunction through damage of the components of the vascular wall, such as vascular smooth muscle cells (VSMCs), which regulate vascular tone and contribute to vascular repair and remodeling. These functions are dependent on intracellular Ca²⁺ changes. The mechanisms by which T2DM affects Ca²⁺ handling in VSMCs still remain poorly understood. Therefore, the objective of this study was to determine whether and how T2DM affects Ca²⁺ homeostasis in VSMCs. We evaluated intracellular Ca²⁺ signaling in VSMCs from Zucker Diabetic Fatty rats using Ca²⁺ imaging with Fura-2/AM. Our results indicate that T2DM decreases Ca²⁺ release from the sarcoplasmic reticulum (SR) and increases the activity of store-operated channels (SOCs). Moreover, we were able to identify an enhancement of the activity of the main Ca²⁺ extrusion mechanisms (SERCA, PMCA and NCX) during the early stage of the decay of the ATP-induced Ca²⁺ transient. In addition, we found an increase in Ca²⁺ entry through the reverse mode of NCX and a decrease in SERCA and PMCA activity during the late stage of the signal decay. These effects were appreciated as a shortening of ATP-induced Ca²⁺ transient during the early stage of the decay, as well as an increase in the amplitude of the following plateau. Enhanced cytosolic Ca²⁺ activity in VSMCs could contribute to vascular dysfunction associated with T2DM.

The Pleiotropic Role of Extracellular ATP in Myocardial Remodelling

Myocardial remodelling is a molecular, cellular, and interstitial adaptation of the heart in response to altered environmental demands. The heart undergoes reversible physiological remodelling in response to changes in mechanical loading or irreversible pathological remodelling induced by neurohumoral factors and chronic stress, leading to heart failure. Adenosine triphosphate (ATP) is one of the potent mediators in cardiovascular signalling that act on the ligand-gated (P2X) and G-protein-coupled (P2Y) purinoceptors via the autocrine or paracrine manners. These activations mediate numerous intracellular communications by modulating the production of other messengers, including calcium, growth factors, cytokines, and nitric oxide. ATP is known to play a pleiotropic role in cardiovascular pathophysiology, making it a reliable biomarker for cardiac protection. This review outlines the sources of ATP released under physiological and pathological stress and its cell-specific mechanism of action. We further highlight a series of cardiovascular cell-to-cell communications of extracellular ATP signalling cascades in cardiac remodelling, which can be seen in hypertension, ischemia/reperfusion injury, fibrosis, hypertrophy, and atrophy. Finally, we summarize current pharmacological intervention using the ATP network as a target for cardiac protection. A better understanding of ATP communication in myocardial remodelling could be worthwhile for future drug development and repurposing and the management of cardiovascular diseases.

Vascular Smooth Muscle Remodeling in Conductive and Resistance Arteries in Hypertension

Cardiovascular disease is a leading cause of death worldwide and accounts for >17.3 million deaths per year, with an estimated increase in incidence to 23.6 million by 2030. ¹ Cardiovascular death represents 31% of all global deaths ² -with stroke, heart attack, and ruptured aneurysms predominantly contributing to these high mortality rates. A key risk factor for cardiovascular disease is hypertension. Although treatment or reduction in hypertension can prevent the onset of cardiovascular events, existing therapies are only partially effective. A key pathological hallmark of hypertension is increased peripheral vascular resistance because of structural and functional changes in large (conductive) and small (resistance) arteries. In this review, we discuss the clinical implications of vascular remodeling, compare the differences between vascular smooth muscle cell remodeling in conductive and resistance arteries, discuss the genetic factors associated with vascular smooth muscle cell function in hypertensive patients, and provide a prospective assessment of current and future research and pharmacological targets for the treatment of hypertension.

Involvement of P2Y12 receptor in vascular smooth muscle inflammatory changes via MCP-1 upregulation and monocyte adhesion

Antiplatelet drugs, frequently used for cardiovascular events with thrombotic involvement, are also regarded as possible promising agents for cardiovascular primary prevention. The roles of P2Y12, an ADP receptor and the target of thienopyridine antiplatelet drugs, are not satisfactorily known in the vascular wall. We investigated the hypothesis that vascular smooth muscle cell (VSMC) P2Y12 is involved in vascular wall inflammatory changes by upregulating monocyte chemoattractant protein-1 (MCP-1) and promoting monocyte adhesion. ADP at 10(-5) M induced a 3.6 ± 0.3-fold upregulation of MCP-1 mRNA in cultured rat VSMCs, which was significantly inhibited by R-138727, the active metabolite of P2Y12 inhibitor prasugrel and siRNAs against P2Y12. ADP also induced MCP-1 protein upregulation, which was diminished by R-138727 and P2Y12 siRNAs. JNK (c-Jun NH2-terminal kinase) inhibition attenuated ADP-induced MCP-1 mRNA and protein upregulation. R-138727 and P2Y12 siRNAs inhibited ADP-induced JNK activation. The reactive oxygen species (ROS) inhibitors N-acetylcysteine (NAC), diphenyleneiodonium (DPI), and Tempol also diminished MCP-1 upregulation and JNK activation induced by ADP. ADP induced MCP-1 promoter activation, which was inhibited by R-138727 and P2Y12 siRNAs. Nuclear factor-κB (NF-κB) consensus sites in the MCP-1 promoter region were involved in this activation. ADP-induced NF-κB pathway activation, examined by a plasmid containing multiple NF-κB sites, was diminished by P2Y12 inhibition. For cellular function analysis, stimulation of VSMC with ADP increased subsequent THP-1 monocyte adhesion. P2Y12 siRNAs and CCR2 antagonism diminished this ADP-induced monocyte adhesion. These data suggested that ADP, via the VSMC P2Y12 receptor, induces vascular inflammatory changes by upregulating MCP-1 and promoting monocyte adhesion.

Nucleoside triphosphate diphosphohydrolase-1 ectonucleotidase is required for normal vas deferens contraction and male fertility through maintaining P2X1 receptor function

In this work, we report that Entpd1(-/-) mice, deficient for the ectonucleotidase nucleoside triphosphate diphosphohydrolase-1 (NTPDase1), produce smaller litters (27% reduction) compared with wild-type C57BL6 animals. This deficit is linked to reduced in vivo oocyte fertilization by Entpd1(-/-) males (61 ± 11% versus 88 ± 7% for Entpd1(+/+)). Normal epididymal sperm count, spermatozoa morphology, capacitation, and motility and reduced ejaculated sperm number (2.4 ± 0.5 versus 3.7 ± 0.4 million for Entpd1(+/+)) pointed to vas deferens dysfunction. NTPDase1 was localized by immunofluorescence in the tunica muscularis of the vas deferens. Its absence resulted in a major ATP hydrolysis deficiency, as observed in situ by histochemistry and in primary smooth muscle cell cultures. In vitro, Entpd1(-/-) vas deferens displayed an exacerbated contraction to ATP, a diminished response to its non-hydrolysable analog αβMeATP, and a reduced contraction to electrical field stimulation, suggesting altered P2X1 receptor function with a propensity to desensitize. This functional alteration was accompanied by a 3-fold decrease in P2X1 protein expression in Entpd1(-/-) vas deferens with no variation in mRNA levels. Accordingly, exogenous nucleotidase activity was required to fully preserve P2X1 receptor activation by ATP in vitro. Our study demonstrates that NTPDase1 is required to maintain normal P2X1 receptor functionality in the vas deferens and that its absence leads to impaired peristalsis, reduced spermatozoa concentration in the semen, and, eventually, reduced fertility. This suggests that alteration of NTPDase1 activity affects ejaculation efficacy and male fertility. This work may contribute to unveil a cause of infertility and open new therapeutic potentials.

FAM3A promotes vascular smooth muscle cell proliferation and migration and exacerbates neointima formation in rat artery after balloon injury

The biological function of FAM3A, the first member of family with sequence similarity 3 (FAM3) gene family, remains largely unknown. This study aimed to determine its role in the proliferation and migration of vascular smooth muscle cells (VSMCs). Immunohistochemical staining revealed that FAM3A protein is expressed in the tunica media of rodent arteries, and its expression is reduced with an increase in prostaglandin E receptor 2 (EP2) expression after injury. In vitro, FAM3A overexpression promotes proliferation and migration of VSMCs, whereas FAM3A silencing inhibits these processes. In vivo, FAM3A overexpression results in exaggerated neointima formation of rat carotid artery after balloon injury. FAM3A activates Akt in a PI3K-dependent manner. In contrast, FAM3A induces ERK1/2 activation independent of PI3K. FAM3A protein is subcellularly located in mitochondria, where it affects ATP production and release. Activation of EP2 represses FAM3A expression, leading to impaired ATP production and release in VSMCs. FAM3A-induced activation of Akt and ERK1/2 pathways, proliferation and migration of VSMCs are inhibited by P2 receptor antagonist suramin. Furthermore, inhibition or knockdown of P2Y1 receptor inihibits FAM3A-induced proliferation and migration of VSMCs. In conclusion, FAM3A promotes proliferation and migration of VSMCs via P2Y1 receptor-mediated activation of Akt and ERK1/2 pathways. In injured vessels, FAM3A was repressed by upregulated EP2 expression, leading to the attenuation of ATP-P2Y1 receptor signaling, which is beneficial for preventing excessive proliferation and migration of VSMCs.

Vasotrophic regulation of age-dependent hypoxic cerebrovascular remodeling

Hypoxia can induce functional and structural vascular remodeling by changing the expression of trophic factors to promote homeostasis. While most experimental approaches have been focused on functional remodeling, structural remodeling can reflect changes in the abundance and organization of vascular proteins that determine functional remodeling. Better understanding of age-dependent hypoxic macrovascular remodeling processes of the cerebral vasculature and its clinical implications require knowledge of the vasotrophic factors that influence arterial structure and function. Hypoxia can affect the expression of transcription factors, classical receptor tyrosine kinase factors, non-classical G-protein coupled factors, catecholamines, and purines. Hypoxia's remodeling effects can be mediated by Hypoxia Inducible Factor (HIF) upregulation in most vascular beds, but alterations in the expression of growth factors can also be independent of HIF. PPARγ is another transcription factor involved in hypoxic remodeling. Expression of classical receptor tyrosine kinase ligands, including vascular endothelial growth factor, platelet derived growth factor, fibroblast growth factor and angiopoietins, can be altered by hypoxia which can act simultaneously to affect remodeling. Tyrosine kinase-independent factors, such as transforming growth factor, nitric oxide, endothelin, angiotensin II, catecholamines, and purines also participate in the remodeling process. This adaptation to hypoxic stress can fundamentally change with age, resulting in different responses between fetuses and adults. Overall, these mechanisms integrate to assure that blood flow and metabolic demand are closely matched in all vascular beds and emphasize the view that the vascular wall is a highly dynamic and heterogeneous tissue with multiple cell types undergoing regular phenotypic transformation.

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.

P2X1 receptor-mediated inhibition of the proliferation of human coronary smooth muscle cells involving the transcription factor NR4A1

Adenine nucleotides acting at P2X1 receptors are potent vasoconstrictors. Recently, we demonstrated that activation of adenosine A2B receptors on human coronary smooth muscle cells inhibits cell proliferation by the induction of the nuclear receptor subfamily 4, group A, member 1 (NR4A1; alternative notation Nur77). In the present study, we searched for long-term effects mediated by P2X1 receptors by analyzing receptor-mediated changes in cell proliferation and in the expression of NR4A1. Cultured human coronary smooth muscle cells were treated with selective receptor ligands. Effects on proliferation were determined by counting cells and measuring changes in impedance. The induction of transcription factors was assessed by qPCR. The P2X receptor agonist α,β-methylene-ATP and its analog β,γ-methylene-ATP inhibited cell proliferation by about 50 % after 5 days in culture with half-maximal concentrations of 0.3 and 0.08 μM, respectively. The effects were abolished or markedly attenuated by the P2X1 receptor antagonist NF449 (carbonylbis-imino-benzene-triylbis-(carbonylimino)tetrakis-benzene-1,3-disulfonic acid; 100 nM and 1 μM). α,β-methylene-ATP and β,γ-methylene-ATP applied for 30 min to 4 h increased the expression of NR4A1; NF449 blocked or attenuated this effect. Small interfering RNA directed against NR4A1 diminished the antiproliferative effects of α,β-methylene-ATP and β,γ-methylene-ATP. α,β-methylene-ATP (0.1 to 30 μM) decreased migration of cultured human coronary smooth muscle cells in a chamber measuring changes in impedance; NF449 blocked the effect. In conclusion, our results demonstrate for the first time that adenine nucleotides acting at P2X1 receptors inhibit the proliferation of human coronary smooth muscle cells via the induction of the early gene NR4A1.

Perivascular innervation: a multiplicity of roles in vasomotor control and myoendothelial signaling

The control of vascular resistance and tissue perfusion reflect coordinated changes in the diameter of feed arteries and the arteriolar networks they supply. Against a background of myogenic tone and metabolic demand, vasoactive signals originating from perivascular sympathetic and sensory nerves are integrated with endothelium-derived signals to produce vasodilation or vasoconstriction. PVNs release adrenergic, cholinergic, peptidergic, purinergic, and nitrergic neurotransmitters that lead to SMC contraction or relaxation via their actions on SMCs, ECs, or other PVNs. ECs release autacoids that can have opposing actions on SMCs. Respective cell layers are connected directly to each other through GJs at discrete sites via MEJs projecting through holes in the IEL. Whereas studies of intercellular communication in the vascular wall have centered on endothelium-derived signals that govern SMC relaxation, attention has increasingly focused on signaling from SMCs to ECs. Thus, via MEJs, neurotransmission from PVNs can evoke distinct responses from ECs subsequent to acting on SMCs. To integrate this emerging area of investigation in light of vasomotor control, the present review synthesizes current understanding of signaling events that originate within SMCs in response to perivascular neurotransmission in light of EC feedback. Although often ignored in studies of the resistance vasculature, PVNs are integral to blood flow control and can provide a physiological stimulus for myoendothelial communication. Greater understanding of these underlying signaling events and how they may be affected by aging and disease will provide new approaches for selective therapeutic interventions.

ATP and arterial calcification

BACKGROUND

Arterial calcification (AC) is a major health problem associated with extreme morbidity and a shortened survival. It is currently without any effective treatment. ATP and the purinergic system in general are now emerging as being important in the pathogenesis of AC and potentially provide a new focus for novel therapies.

METHODS

This review systematically analyses and discusses the current literature examining the relevance of the purinergic system to AC. Particular emphasis is given to the enzymes associated with ATP metabolism and their role in maintaining a balance between promotion and inhibition of arterial mineralization. Points of controversy are highlighted, and areas for future research are suggested.

CONCLUSION

The potential roles of ATP and the purinergic system in AC are beginning to be elucidated. While further work is necessary, current knowledge suggests that several components of the purinergic system could be targeted to develop new treatments for AC.

P2Y receptor subtypes evoke different Ca2+ signals in cultured aortic smooth muscle cells

Adenine and uridine nucleotides evoke Ca(2+) signals via four subtypes of P2Y receptor in cultured aortic smooth muscle cells, but the mechanisms underlying the different patterns of these Ca(2+) signals are unresolved. Cytosolic Ca(2+) signals were recorded from single cells and populations of cultured rat aortic smooth muscle cells, loaded with a fluorescent Ca(2+) indicator and stimulated with agonists that allow subtype-selective activation of P2Y1, P2Y2, P2Y4, or P2Y6 receptors. Activation of P2Y1, P2Y2, and P2Y6 receptors caused homologous desensitisation, while activation of P2Y2 receptors also caused heterologous desensitisation of the other subtypes. The Ca(2+) signals evoked by each P2Y receptor subtype required activation of phospholipase C and release of Ca(2+) from intracellular stores via inositol 1,4,5-trisphosphate (IP(3)) receptors, but they were unaffected by inhibition of ryanodine or nicotinic acid adenine dinucleotide phosphate (NAADP) receptors. Sustained Ca(2+) signals were independent of the Na(+)/Ca(2+) exchanger and were probably mediated by store-operated Ca(2+) entry. Analyses of single cells established that most cells express P2Y2 receptors and at least two other P2Y receptor subtypes. We conclude that four P2Y receptor subtypes evoke Ca(2+) signals in cultured aortic smooth muscle cells using the same intracellular (IP(3) receptors) and Ca(2+) entry pathways (store-operated Ca(2+) entry). Different rates of homologous desensitisation and different levels of receptor expression account for the different patterns of Ca(2+) signal evoked by each P2Y receptor subtype.

Signaling mechanisms mediating uridine adenosine tetraphosphate-induced proliferation of human vascular smooth muscle cells

Proliferation of vascular smooth muscle cells (SMCs) plays an important role in the development of atherosclerosis and restenosis. Extracellular mononucleotides, such as adenosine triphosphate and uridine-5'-triphosphate stimulate SMC proliferation. However, the effects of dinucleotides on SMC proliferation and their underlying signaling mechanisms are less well defined. Recently, increasing evidence suggests that the dinucleotide, uridine adenosine tetraphosphate (Up4A) plays a role in the regulation of cardiovascular function. We have previously demonstrated that Up4A stimulates DNA synthesis and proliferation of human SMCs. This study investigated the signaling mechanisms underlying the proliferative effect of Up4A. Up4A-induced increase in bromodeoxyuridine incorporation was blocked by the mammalian target of rapamycin inhibitor, rapamycin, and the MEK inhibitor, PD98059. Up4A-stimulated phosphorylation and kinase activity of S6 kinase (S6K) and Erk1/2 were inhibited by PD98059, whereas phosphorylation and kinase activity of S6K, but not Erk1/2, were inhibited by rapamycin. Up4A also increased the phosphorylation of Akt, which was blocked by the PI3-kinase inhibitor, LY294002. Up4A-stimulated activation of S6K, but not Erk1/2, was also prevented by LY294002. Furthermore, Up4A-stimulated phosphorylation and kinase activity of S6K and Erk1/2 were inhibited by the P2 receptor antagonist, suramin, but not by the P2X receptor antagonist, Ip5I. Up4A also stimulated an increase in the protein expression of cycle-dependent kinase 2, which was prevented by rapamycin, PD98059, and suramin. These results suggest that the signaling mechanisms underlying the Up4A-stimulated proliferation of SMCs are mediated by P2Y receptors and involve the PI3-K/Akt and mitogen-activated protein kinase pathways, leading to the independent activation of S6K and an increase in cycle-dependent kinase 2 expression. This work stresses the concept that dinucleotides, like mononucleotides, play potentially important roles in the regulation of vascular function.

P2Y2 receptor-mediated lymphotoxin-α secretion regulates intercellular cell adhesion molecule-1 expression in vascular smooth muscle cells

The proinflammatory cytokine lymphotoxin-α (LTA) is thought to contribute to the pathogenesis of atherosclerosis. However, the mechanisms that regulate its expression in vascular smooth muscle cells (VSMC) are poorly understood. The ability of exogenous nucleotides to stimulate LTA production was evaluated in VSMC by ELISA. The P2Y(2) nucleotide receptor (P2Y(2)R) agonist UTP stimulates a strong and sustained release of LTA from WT but not P2Y(2)R(-/-) SMC. Assessment of LTA gene transcription by LTA promoter-luciferase construct indicated that LTA levels are controlled at the level of transcription. We show using RNAi techniques that knockdown of the actin-binding protein filamin-A (FLNa) severely impaired nucleotide-induced Rho activation and consequent Rho-mediated LTA secretion. Reintroduction of FLNa in FLNa RNAi SMC rescued UTP-induced LTA expression. In addition, we found that UTP-stimulated LTA secretion is not sensitive to brefeldin A, which blocks the formation of vesicles involved in protein transport from the endoplasmic reticulum to the Golgi apparatus, suggesting that P2Y(2)R/filamin-mediated secretion of LTA is independent of the endoplasmic reticulum/Golgi secretory vesicle route. Furthermore, UTP selectively induces ICAM-1 expression in WT but not SMC expressing a truncated P2Y(2)R deficient in LTA secretion. These data suggest that P2Y(2)R recruits FLNa to provide a cytoskeletal scaffold necessary for Rho signaling pathway upstream of LTA release and subsequent stimulation of ICAM-1 expression on vascular smooth muscle cells.

Remodeling of purinergic receptor-mediated Ca2+ signaling as a consequence of EGF-induced epithelial-mesenchymal transition in breast cancer cells

Background

The microenvironment plays a pivotal role in tumor cell proliferation, survival and migration. Invasive cancer cells face a new set of environmental challenges as they breach the basement membrane and colonize distant organs during the process of metastasis. Phenotypic switching, such as that which occurs during epithelial-mesenchymal transition (EMT), may be associated with a remodeling of cell surface receptors and thus altered responses to signals from the tumor microenvironment.

Methodology/Principal Findings

We assessed changes in intracellular Ca²⁺ in cells loaded with Fluo-4 AM using a fluorometric imaging plate reader (FLIPR^TETRA) and observed significant changes in the potency of ATP (EC₅₀ 0.175 µM (−EGF) versus 1.731 µM (+EGF), P<0.05), and the nature of the ATP-induced Ca²⁺ transient, corresponding with a 10-fold increase in the mesenchymal marker vimentin (P<0.05). We observed no change in the sensitivity to PAR2-mediated Ca²⁺ signaling, indicating that these alterations are not simply a consequence of changes in global Ca²⁺ homeostasis. To determine whether changes in ATP-mediated Ca²⁺ signaling are preceded by alterations in the transcriptional profile of purinergic receptors, we analyzed the expression of a panel of P2X ionotropic and P2Y metabotropic purinergic receptors using real-time RT-PCR and found significant and specific alterations in the suite of ATP-activated purinergic receptors during EGF-induced EMT in breast cancer cells. Our studies are the first to show that P2X₅ ionotropic receptors are enriched in the mesenchymal phenotype and that silencing of P2X₅ leads to a significant reduction (25%, P<0.05) in EGF-induced vimentin protein expression.

Conclusions

The acquisition of a new suite of cell surface purinergic receptors is a feature of EGF-mediated EMT in MDA-MB-468 breast cancer cells. Such changes may impart advantageous phenotypic traits and represent a novel mechanism for the targeting of cancer metastasis.

Uridine adenosine tetraphosphate-induced contraction is increased in renal but not pulmonary arteries from DOCA-salt hypertensive rats

Uridine adenosine tetraphosphate (Up(4)A) was reported as a novel endothelium-derived contracting factor. Up(4)A contains both purine and pyrimidine moieties, which activate purinergic (P2)X and P2Y receptors. However, alterations in the vasoconstrictor responses to Up(4)A in hypertensive states remain unclear. The present study examined the effects of Up(4)A on contraction of isolated renal arteries (RA) and pulmonary arteries (PA) from DOCA-salt rats using isometric tension recording. RA from DOCA-salt rats exhibited increased contraction to Up(4)A versus arteries from control uninephrectomized rats in the absence and presence of N(G)-nitro-l-arginine (nitric oxide synthase inhibitor). On the other hand, the Up(4)A-induced contraction in PA was similar between the two groups. Up(4)A-induced contraction was inhibited by suramin (nonselective P2 antagonist) but not by diinosine pentaphosphate pentasodium salt hydrate (Ip(5)I; P2X(1) antagonist) in RA from both groups. Furthermore, 2-thiouridine 5'-triphosphate tetrasodium salt (2-ThioUTP; P2Y(2) agonist)-, uridine-5'-(γ-thio)-triphosphate trisodium salt (UTPγS; P2Y(2)/P2Y(4) agonist)-, and 5-iodouridine-5'-O-diphosphate trisodium salt (MRS 2693; P2Y(6) agonist)-induced contractions were all increased in RA from DOCA-salt rats. Protein expression of P2Y(2)-, P2Y(4)-, and P2Y(6) receptors in RA was similar between the two groups. In DOCA-salt RA, the enhanced Up(4)A-induced contraction was reduced by PD98059, an ERK pathway inhibitor, and Up(4)A-stimulated ERK activation was increased. These data are the first to indicate that Up(4)A-induced contraction is enhanced in RA from DOCA-salt rats. Enhanced P2Y receptor signaling and activation of the ERK pathway together represent a likely mechanism mediating the enhanced Up(4)A-induced contraction. Up(4)A might be of relevance in the pathophysiology of vascular tone regulation and renal dysfunction in arterial hypertension.

Ca(2+) signalling by P2Y receptors in cultured rat aortic smooth muscle cells

Background and purpose:

P2Y receptors evoke Ca²⁺ signals in vascular smooth muscle cells and regulate contraction and proliferation, but the roles of the different P2Y receptor subtypes are incompletely resolved.

Experimental approach:

Quantitative PCR was used to define expression of mRNA encoding P2Y receptor subtypes in freshly isolated and cultured rat aortic smooth muscle cells (ASMC). Fluorescent indicators in combination with selective ligands were used to measure the changes in cytosolic free [Ca²⁺] in cultured ASMC evoked by each P2Y receptor subtype.

Key results:

The mRNA for all rat P2Y receptor subtypes are expressed at various levels in cultured ASMC. Four P2Y receptor subtypes (P2Y1, P2Y2, P2Y4 and P2Y6) evoke Ca²⁺ signals that require activation of phospholipase C and comprise both release of Ca²⁺ from stores and Ca²⁺ entry across the plasma membrane.

Conclusions and implications:

Combining analysis of P2Y receptor expression with functional analyses using selective agonists and antagonists, we isolated the Ca²⁺ signals evoked in ASMC by activation of P2Y1, P2Y2, P2Y4 and P2Y6 receptors.

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.

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.

S1P receptor signalling and RGS proteins; expression and function in vascular smooth muscle cells and transfected CHO cells

Sphingosine-1-phosphate (S1P) signalling via G protein-coupled receptors is important for the regulation of cell function and differentiation. Specific Regulators of G protein Signalling (RGS) proteins modulate the function of these receptors in many cell types including vascular smooth muscle cells (VSMCs). Therefore, we investigated the role of altered expression levels of RGS proteins in S1P receptor function in VSMCs and transfected CHO cells. The mRNA expression of the S1P(1) receptor, RGS4 and RGS16 were down-regulated in VSMCs during phenotypic modulation induced by culturing, whereas mRNA levels of RGS2, RGS3, S1P(2) and S1P(3) receptors were unchanged. Interestingly, the expression level of RGS5 was transiently up-regulated. Despite major alterations in RGS levels, S1P-induced calcium elevation in VSMCs was not altered. Co-transfection of RGS2, RGS3, RGS4, RGS5 and RGS16 into CHO-Flp-In cells stably expressing the S1P(1) or S1P(3) receptor did not modify S1P-induced inhibition of cAMP accumulation to a major extent. Similar results were obtained with SEW2871, a selective S1P(1) receptor agonist. However, the inhibition of cAMP accumulation by the agonist FTY720-P via the S1P(1) receptor was significantly decreased by co-transfection with RGS5. These results indicate that mRNA of the S1P(1) receptor, RGS4, RGS5 and RGS16 is differentially regulated during phenotypic modulation. However, major alterations in RGS protein expression have only limited effect on S1P receptor function.

Reduced Atherosclerotic Lesions in P2Y 1 /Apolipoprotein E Double-Knockout Mice

Background— The P2Y 1 receptor plays a key role in arterial thrombosis and is widely expressed in many cell types involved in atherosclerosis. The aim of this study was to evaluate its potential involvement in the development of atherosclerotic lesions.

Methods and Results— Apolipoprotein E–deficient ( ApoE −/− ) and P2Y 1 −/− / ApoE −/− mice were maintained on regular chow for 17 or 30 weeks before analysis of atherosclerotic lesions. At 17 weeks, lesions in the aortic sinus and entire aorta were smaller in P2Y 1 −/− / ApoE −/− compared with those in ApoE −/− animals. At 30 weeks, the aortic sinus lesions in P2Y 1 −/− / ApoE −/− mice were still diminished in size and displayed reduced inflammation, reflected by decreased macrophage infiltration and diminished VCAM-1 immunostaining, compared with those in ApoE −/− mice. They also had a lower smooth muscle cell content. Unexpectedly, bone marrow transplantation showed that the absence of the P2Y 1 receptor in blood cells only led to no significant modification of the lesion compared with control ApoE −/− reconstituted animals. Conversely, the absence of the P2Y 1 receptor except in blood cells resulted in a reduction in lesion size similar to that in control P2Y 1 −/− / ApoE −/− reconstituted mice, pointing to a role of non–hematopoietic-derived P2Y 1 receptors, most likely the endothelial or smooth muscle cell P2Y 1 receptors. In addition, although this was not statistically significant, plasma cholesterol levels were consistently decreased in P2Y 1 −/− animals, suggesting that a modification of lipid metabolism could be responsible for the observed phenotype.

Conclusion— The P2Y 1 receptor contributes to atherosclerosis, primarily through its role in non–hematopoietic-derived cells.

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.

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.

Alterations in Purinoceptor Expression in Human Long Saphenous Vein during Varicose Disease

OBJECTIVES

Varicose veins are dilated tortuous veins of varying tone. Purinergic signalling is important in the control of tone and in mediating trophic changes in blood vessels. The expression of P2 receptors in control and varicose veins will be examined.

METHODS

Purinergic signalling in circular and longitudinal smooth muscle of the human long saphenous vein was studied in control and varicose tissues using immunohistochemistry, organ bath pharmacology and electron microscopy.

RESULTS

P2X1, P2Y1, P2Y2, P2Y4 and P2Y6 receptors were present on circular and longitudinal smooth muscle. Purine-mediated circular and longitudinal muscle contractions were weaker in varicose veins. Electron microscopy and immunohistochemistry findings support the view that smooth muscle cells change from the contractile to synthetic phenotype in varicose veins, associated with an upregulation of P2Y1 and P2Y2 receptors and a down regulation of P2X1 receptors.

CONCLUSIONS

Down regulation of P2X1 receptors on the smooth muscle of varicose veins is associated with loss of contractile activity. Upregulation of P2Y1 and P2Y2 receptors is associated with a shift from contractile to synthetic and/or proliferative roles. The phenotype change in smooth muscle is associated with weakening of vein walls and may be a causal factor in the development of varicose veins.

Diguanosine pentaphosphate: an endogenous activator of Rho-kinase possibly involved in blood pressure regulation

OBJECTIVE

Rho-kinase activity is increased in cardiovascular disease and in the pathophysiology of hypertension. Few endogenous factors are known that activate the Rho-kinase pathway. Stimulation of P2Y receptors activates the Rho-kinase pathway. Recently identified diguanosine pentaphosphate (Gp5G) possibly activates P2Y receptors. In this study, Gp5G was identified and quantified in human plasma. The influence of Gp5G on vascular tone was studied.

METHODS

Gp5G in human plasma was purified to homogeneity by several steps. Gp5G was quantified and identified by matrix-assisted laser desorption/ionization mass spectrometry and enzymatic analysis. The vasoactive effects of Gp5G were studied in the isolated perfused rat kidney and after intra-aortic application. Activation of Rho-kinase was measured using western blot analysis.

RESULTS

The plasma level of Gp5G in healthy donors is 9.47 +/- 4.97 nmol/l. Gp5G increases contractile responses induced by angiotensin II in a dose-dependent way [ED50 (-log mol) angiotensin II: 10.9 +/- 0.1; angiotensin II plus Gp5G (100 nmol/l): 11.5 +/- 0.1]. P2 receptor antagonists inhibited the Gp5G-induced increase in angiotensin II vasoconstriction. MRS2179, a selective P2Y1 receptor antagonist, had no effect on Gp5G-mediated angiotensin II potentiation. Rho-kinase inhibition by Y27632 abolished the Gp5G-induced increase of contractile responses to angiotensin II. Concentrations of 10 nmol/l Gp5G activated the translocation of RhoA from the cytosolic to the membranous fraction indicating the activation of Rho-kinase. The intra-aortic application of 100 pmol Gp5G significantly increased mean arterial blood pressure by 13.5 +/- 4.2 mmHg.

CONCLUSION

Gp5G is an endogenous activator of Rho-kinase, which might affect vascular tone control by Rho-kinase at physiological levels. Gp5G activates P2Y4&6 receptors, and might play a role in physiological and pathophysiological vascular tone control.

P2 receptor web: Complexity and fine-tuning

The present review offers a new perspective on a family of receptors, termed P2 receptors, specific for nucleoside tri- and diphosphates of purines/pyrimidines. We emphasize here that while decoding the inputs of various related extracellular ligands, P2 receptors are a clear example of increasing biological complexity. They are represented by 7 ionotropic P2X and 8 metabotropic P2Y receptors; they have very heterogeneous ligands and binding characteristics, molecular properties, transduction mechanisms, cellular localization and protein-protein interactions. While the reason for this sophistication is unknown, a few compelling issues emerge while looking at such a rich variety. We ask, for instance, why so many different receptor subtypes are necessary for triggering biological properties and functions, and if these receptors are more than the sum of their single entities. A first possibility is that newly synthesized P2 proteins are casually located on the cell surface (stochastic hypothesis). Alternatively, distinct subunits are engaged on different cell phenotypes by genetic control (genetic determinism) and/or selective recruitment under physiopathological conditions and epigenetic stimuli (epigenetic determinism). Nevertheless, an appropriate way to both dissect the vast biological scenario and molecular complexity among P2 receptors and to integrate and upgrade their assortment is to regard them as a "combinatorial receptor web", that is, a dynamic architecture of P2 proteins demonstrating economic efficiency and involving a process of "fine-tuning", a mechanism which endorses the dynamic nature of all biological reactions. In the present analysis, we stimulate a scientific query about what contributes to such a vast P2 receptor sophistication.

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.

Pathophysiology and therapeutic potential of purinergic signaling

The concept of a purinergic signaling system, using purine nucleotides and nucleosides as extracellular messengers, was first proposed over 30 years ago. After a brief introduction and update of purinoceptor subtypes, this article focuses on the diverse pathophysiological roles of purines and pyrimidines as signaling molecules. These molecules mediate short-term (acute) signaling functions in neurotransmission, mechanosensory transduction, secretion and vasodilatation, and long-term (chronic) signaling functions in cell proliferation, differentiation, and death involved in development and regeneration. Plasticity of purinoceptor expression in pathological conditions is frequently observed, including an increase in the purinergic component of autonomic cotransmission. Recent advances in therapies using purinergic-related drugs in a wide range of pathological conditions will be addressed with speculation on future developments in the field.

ATP stimulates MMP-2 release from human aortic smooth muscle cells via JNK signaling pathway

Aortic smooth muscle cell release of matrix metalloproteinase-2 (MMP-2) and tissue inhibitor of metalloproteinase-2 (TIMP-2) has been implicated in aortic aneurysm pathogenesis, but proximal modulation of release is poorly understood. Extracellular nucleotides regulate vascular smooth muscle cell metabolism in response to physiochemical stresses, but nucleotide modulation of MMP and/or TIMP release has not been reported. We hypothesized that nucleotides modulate MMP-2 and TIMP-2 release from human aortic smooth muscle cells (HASMCs) via distinct purinergic receptors and signaling pathways. We exposed HASMCs to exogenous ATP and other nucleotides with and without interleukin-1beta (IL-1beta). HASMCs were pretreated in some experiments with apyrase, which degrades ATP, and inhibitors of ERK1/2, JNK, and p38 MAPK. MMP-2 and TIMP-2 released into supernatant were assessed using ELISA and Western blotting. ATP, adenosine, and UTP significantly stimulated MMP-2 release in the presence of IL-1beta (300 nM ATP: 181 +/- 22%, P = 0.003; 30 microm adenosine: 244 +/- 150%, P = 0.001; and 200 microm UTP: 153 +/- 40%, P = 0.015; vs. 100% constitutive). ATP also stimulated MMP-2 release in the absence of IL-1beta (100 microm ATP: 148 +/- 38% vs. 100% constitutive). Apyrase significantly reduced ATP-stimulated MMP-2 release (apyrase + 500 nM ATP: 59 +/- 3% vs. 124 +/- 7% with 500 nM ATP). Rank-order agonist potency for MMP-2 release was consistent with ATP activation of PAY and PAY receptors. ATP induced phosphorylation of intracellular JNK, and inhibition of the JNK pathway blocked ATP-stimulated MMP-2 release, indicating signaling via this pathway. Nucleotides are thus novel stimulants of MMP-2 release from HASMCs and may provide a mechanistic link between physiochemical stress in the aorta and aneurysms, especially in the context of inflammation.

Pharmacological profiles of cloned mammalian P2Y-receptor subtypes

Membrane-bound P2-receptors mediate the actions of extracellular nucleotides in cell-to-cell signalling. P2X-receptors are ligand-gated ion channels, whereas P2Y-receptors belong to the superfamily of G-protein-coupled receptors (GPCRs). So far, the P2Y family is composed out of 8 human subtypes that have been cloned and functionally defined; species orthologues have been found in many vertebrates. P2Y1-, P2Y2-, P2Y4-, P2Y6-, and P2Y11-receptors all couple to stimulation of phospholipase C. The P2Y11-receptor mediates in addition a stimulation of adenylate cyclase. In contrast, activation of the P2Y12-, P2Y13-, and P2Y14-receptors causes an inhibition of adenylate cyclase activity. The expression of P2Y1-receptors is widespread. The receptor is involved in blood platelet aggregation, vasodilatation and neuromodulation. It is activated by ADP and ADP analogues including 2-methylthio-ADP (2-MeSADP). 2'-Deoxy-N6-methyladenosine-3',5'-bisphosphate (MRS2179) and 2-chloro-N6-methyl-(N)-methanocarba-2'-deoxyadenosine 3',5'-bisphosphate (MRS2279) are potent and selective antagonists. P2Y2 transcripts are abundantly distributed. One important example for its functional role is the control of chloride ion fluxes in airway epithelia. The P2Y2-receptor is activated by UTP and ATP and blocked by suramin. The P2Y2-agonist diquafosol is used for the treatment of the dry eye disease. P2Y4-receptors are expressed in the placenta and in epithelia. The human P2Y4-receptor has a strong preference for UTP as agonist, whereas the rat P2Y4-receptor is activated about equally by UTP and ATP. The P2Y4-receptor is not blocked by suramin. The P2Y6-receptor has a widespread distribution including heart, blood vessels, and brain. The receptor prefers UDP as agonist and is selectively blocked by 1,2-di-(4-isothiocyanatophenyl)ethane (MRS2567). The P2Y11-receptor may play a role in the differentiation of immunocytes. The human P2Y11-receptor is activated by ATP as naturally occurring agonist and it is blocked by suramin and reactive blue 2 (RB2). The P2Y12-receptor plays a crucial role in platelet aggregation as well as in inhibition of neuronal cells. It is activated by ADP and very potently by 2-methylthio-ADP. Nucleotide antagonists including N6-(2-methylthioethyl)-2-(3,3,3-trifluoropropylthio)-beta,gamma-dichloromethylene-ATP (=cangrelor; AR-C69931MX), the nucleoside analogue AZD6140, as well as active metabolites of the thienopyridine compounds clopidogrel and prasugrel block the receptor. These P2Y12-antagonists are used in pharmacotherapy to inhibit platelet aggregation. The P2Y13-receptor is expressed in immunocytes and neuronal cells and is again activated by ADP and 2-methylthio-ADP. The 2-chloro-5-nitro pyridoxal-phosphate analogue 6-(2'-chloro-5'-nitro-azophenyl)-pyridoxal-alpha5-phosphate (MRS2211) is a selective antagonist. mRNA encoding for the human P2Y14-receptor is found in many tissues. However, a physiological role of the receptor has not yet been established. UDP-glucose and related analogues act as agonists; antagonists are not known. Finally, UDP has been reported to act on receptors for cysteinyl leukotrienes as an additional agonist--indicating a dual agonist specificity of these receptors.

Differential Regulation of Ca2+ Signaling and Membrane Trafficking by Multiple P2 Receptors in Brown Adipocytes

Extracellular ATP triggers changes in intracellular Ca(2+), ion channel function, and membrane trafficking in adipocytes. The aim of the present study was to determine which P2 receptors might mediate the Ca(2+) signaling and membrane trafficking responses to ATP in brown fat cells. RT-PCR was used to determine which P2 receptors are expressed in brown fat cells. Responses to nucleotide agonists and antagonists were characterized using fura-2 fluorescence imaging of Ca(2+) responses, and FM 1-43 fluorescence imaging and membrane capacitance measurements to assess membrane trafficking. The pharmacology of the Ca(2+) responses fits the properties of the P2Y receptors for which mRNA is expressed, but the agonist and antagonist sensitivity of the membrane-trafficking response was not consistent with any P2 receptor described to date. Brown adipocytes expressed mRNA for P2Y(2), P2Y(6), and P2Y(12) metabotropic receptors and P2X(1), P2X(2), P2X(3), P2X(4), P2X(5), and P2X(7) ionotropic receptors. The agonists ATP, ADP, UTP, UDP and 2', 3'-(benzoylbenzoyl) ATP (BzATP) increased intracellular Ca(2+), while 100 microM: suramin, pyridoxal-phosphate-6-azophenyl-2' 4'-disulfonic acid (PPADS), or Reactive Blue 2 partially blocked Ca(2+) responses. ATP, but not ADP, UTP, UDP or BzATP activated membrane trafficking. The membrane response could be blocked completely with 1 microM: PPADS but not by the antagonist MRS2179. We conclude that multiple P2 receptors mediate the ATP responses of brown fat cells, and that membrane trafficking is regulated by a P2 receptor showing unusual properties.

Biochemical and functional evidence for heteromeric assembly of P2X1 and P2X4 subunits

P2X receptors are ligand-gated ion channels activated by extracellular ATP. In expression systems, P2X subunits form homo- and heterotrimeric receptors. Heteromerization is also likely to occur in vivo as (i) most P2X subunits show overlapping distribution in different tissues and (ii) the functional properties of many native P2X receptors differ from those of heterologously expressed homomeric receptors. Here, we used the Xenopus laevis oocyte expression system to test for heteromerization of P2X1 and P2X4 subunits. Upon co-injection, P2X4 subunits were co-purified with hexahistidyl-tagged P2X1 subunits indicating heteromerization. Blue native polyacrylamide gel electrophoresis (BN-PAGE) analysis of these P2X complexes excluded artificial aggregation and confirmed that both subunits were present in trimeric complexes of the same size. Two-electrode voltage-clamp experiments revealed functional P2X receptors with kinetic properties resembling homomeric P2X4 receptors and a pharmacological profile similar to homomeric P2X1 receptors. Thus, application of alpha,beta-methylene ATP evoked a slowly desensitizing current sensitive to the antagonists suramin and 2',3'-O-(2,4,6-trinitrophenyl)-ATP. This study provides for the first time biochemical and functional evidence for the formation of heteromeric P2X(1+4) receptors. These receptors may account for native P2X mediated responses that until now could not be correlated with previously described recombinant P2X receptors.

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.

Purinergic Signalling to Rat Ovarian Smooth Muscle: Changes in P2X Receptor Expression during Pregnancy

The expression of P2X and P2Y receptor subtypes in the smooth muscle of the rat ovary during the oestrus cycle and pregnancy was examined using immunohistochemistry. RT-PCR studies of P2X receptor mRNA were also carried out. In the non-pregnant rats, P2X2 receptor protein was dominant in the smooth muscle of perifollicular rings and blood vessels. P2X1 protein expression was seen on vascular smooth muscle too, but little, if any, was present on perifollicular smooth muscle. No changes in P2X1 or P2X2 receptor expression were seen during the oestrous cycle. During early and mid-late pregnancy, there was a switch from P2X2 to P2X1 receptor protein expression in the smooth muscle of the perifollicular ring; P2X1 receptors were also more prominently expressed than P2X2 receptors on ovarian vascular smooth muscle in non-pregnant animals, but during late pregnancy the expression of P2X2 receptors was found to equal that of the P2X1 receptors. There was a return to non-pregnant P2 receptor subtype distribution 2 days after birth. Ovarian vascular and perifollicular smooth muscle showed immunoreactivity for P2Y1, but not for P2X3-7, P2Y2 or P2Y4 receptors. P2Y1 receptor expression in ovarian smooth muscle of both blood vessels and follicular rings did not show significant changes during the oestrus cycle or pregnancy. RT-PCR studies indicated that P2X1 and P2X2 receptor mRNA was present in the ovary during pregnant and non-pregnant conditions. P2X4-6 receptor mRNA was also present in all stages studied, however no immunostaining showing receptor protein for these subtypes was seen on the ovarian sections examined. In summary, purinergic signalling to ovarian perifollicular smooth muscle changed from P2X2 to P2X1 receptors during pregnancy, while there was an increase in P2X2 receptor expression on vascular smooth muscle.

Role of the Rhoa/Rho Kinase System in Flow-Related Remodeling of Rat Mesenteric Small Arteries in Vivo

In small arteries, a chronic blood flow reduction leads to inward hypotrophic remodeling, while a chronic blood flow elevation induces outward hypertrophic remodeling. The RhoA/Rho kinase system was shown to be modulated by shear stress, and to be involved in other kinds of vascular remodeling. The aim of this study was to investigate the role of RhoA/Rho kinase in flow-related small artery remodeling. Rat mesenteric small arteries were subjected to flow-modifying surgery. After 1, 2, 4, 16, and 32 days, the animals were sacrificed and small arteries were harvested. Messenger RNA was isolated and amplified. Using cDNA microarray analysis, the differential expression of >14,000 genes was analyzed, part of which was confirmed by RT-PCR. In vivo treatment with fasudil (3 mg/kg/day s.c.) was used to test the effect of Rho kinase inhibition. The main findings are that: (1) blood flow alteration modified the expression of approximately 5% of the genes by >2-fold, (2) flow reduction downregulated many RhoA-related cytoskeletal markers of smooth muscle cell phenotype, (3) many RhoA-related genes were rapidly (<1 day) regulated and (4) fasudil treatment potentiated the inward hypotrophic remodeling in response to chronically reduced flow. These results indicate the importance of the RhoA/Rho kinase system in flow-related small artery remodeling.

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.

Increased mitogenic and decreased contractile P2 receptors in smooth muscle cells by shear stress in human vessels with intact endothelium

OBJECTIVE

We investigated the role of shear stress in regulating P2 receptors in human umbilical vein.

METHODS AND RESULTS

Using a novel, computerized, biomechanical perfusion model, parallel vessel segments were randomized to simultaneous perfusion under high (25 dyn/cm2) or low (<4 dyn/cm2) shear stress at identical mean perfusion pressure (20 mm Hg) for 6 hours. In the endothelium, no significant P2 receptor mRNA differences were found. In smooth muscle cells (SMCs), high shear stress decreased P2X1 receptors, whereas P2Y2 and P2Y6 receptors were upregulated. These findings were consistent at the mRNA level (real-time reverse transcription-polymerase chain reaction), protein level (Western blot), and morphologically (immunohistochemistry). The changes were more pronounced in the subintimal layer of the media.

CONCLUSIONS

Our findings suggest that shear stress might regulate gene expression in SMCs more than in the endothelium in intact vessels. Decreased expression of the contractile P2X1 receptor could lead to reduced vascular tonus and increased blood flow. Because P2Y2 and P2Y6 receptors stimulate growth and migration of SMCs, increased expression of these receptors could promote vascular remodeling induced by shear stress. The pattern of upregulation of mitogenic P2Y receptors and downregulation of contractile P2X1 receptor is similar to changes seen in the phenotypic shift from contractile to synthetic SMCs.

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.

Isolation and characterization of a dopa decarboxylase cDNA and the induction of its expression by an insect cytokine, growth-blocking peptide in Pseudaletia separata

Parasitization by the wasp, Cotesia kariyai, elevates the concentration of an insect cytokine, growth-blocking peptide (GBP), in hemolymph of last instar Pseudaletis separata larvae. The increase of epidermal and hemolymph dopamine level is associated with the GBP increase. Both GBP and dopamine disturb host development and metamorphosis (Hayakawa, 1995). Dopa decarboxylase (DDC) converts Dopa to dopamine, and its cDNA was isolated from P. separata, and the deduced amino acid sequence showed that it was highly homologous to other lepidopteran DDCs, showing 96, 90 and 86% identity with those of Mamestra brassicae, Bombyx mori, and Manduca sexta, respectively. A 3.2 kb DDC mRNA transcript was constitutively expressed at low levels in the epidermis, brain-nerve cord and hemocytes, and the expression was enhanced by injection of GBP in these tissues. Detailed characterization of the DDC mRNA expression in the epidermis showed that its expression reached a plateau 3 hr after the injection. DDC activity and DDC protein (55 kDa) level mirrored the mRNA expression. Immunocytochemistry with anti-DDC antibody confirmed that the enhanced DDC expression was localized in the epidermal cells. Dopamine concentration in the epidermis gradually increased and reached maximum 6 hr after the injection. When the epidermis of Day 1 last instar larvae was cultured in vitro in the presence of GBP, DDC mRNA increased, indicating that GBP acted on the epidermal cells directly to induce expression of the DDC gene.

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.

P2X(1) receptor-deficient mice establish the native P2X receptor and a P2Y6-like receptor in arteries

The contribution of P2 receptors to vasoconstriction of mouse mesenteric arteries was determined using wild-type (WT) and P2X(1) receptor-deficient (KO) animals. alpha,beta-methylene ATP (alpha,beta-meATP) and ATP evoked transient inward currents and constrictions of WT mesenteric arteries. In contrast, alpha,beta-meATP (100 microM) and ATP (100 microM) failed to evoke responses in KO arteries from a range of vascular beds. Nerve stimulation (100 pulses at 10 Hz) evoked constrictions of mesenteric arteries. For WT arteries, the P2 receptor antagonist pyridoxalphosphate-6-azophenyl-2'-5'-disulfonate (PPADS) (30 microM) reduced the amplitude of response by approximately 50%; the residual constriction was abolished by prazosin (0.1 microM). In KO mice, vasoconstriction induced by nerve stimulation was reduced in amplitude by approximately 50%, unaffected by PPADS, but was abolished by prazosin. ADP (1 mM) (a P2Y(1), P2Y(12), and P2Y(13) receptor agonist) was ineffective. Because ATP had no effect on mesenteric artery tone from KO mice, this rules out the contribution of P2Y(2) receptors. The P2Y(4) receptor agonist ITP also failed to contract mesenteric arteries. However, UTP and UDP evoked sustained contractions of mesenteric arteries with similar potency (EC(50) approximately 10 microM). Complementary studies using reverse-transcriptase polymerase chain reaction showed that mesenteric arteries express P2Y(1), P2Y(2), and P2Y(6) receptors. These results demonstrate that homomeric P2X(1) receptors underlie the artery smooth muscle P2X receptor phenotype and contribute approximately 50% to sympathetic neurogenic vasoconstriction and indicate the presence of a UTP- and UDP-sensitive P2Y(6)-like receptor, but not vasoconstrictor P2Y(2) or P2Y(4) receptors, on mouse mesenteric arteries.

Functional P2Y2 nucleotide receptors mediate uridine 5'-triphosphate-induced intimal hyperplasia in collared rabbit carotid arteries

BACKGROUND

Extracellular uridine 5'-triphosphate (UTP) induces mitogenic activation of smooth muscle cells (SMCs) through binding to P2Y2 nucleotide receptors. P2Y2 receptor mRNA is upregulated in intimal lesions of rat aorta, but it is unclear how this G-protein-coupled receptor contributes to development of intimal hyperplasia.

METHODS AND RESULTS

This study used a silicone collar placed around rabbit carotid arteries to induce vascular injury and intimal thickening. Collar placement caused rapid upregulation of P2Y2 receptor mRNA in medial SMCs before appearance of neointima. Fura-2 digital imaging of single SMCs was used to measure changes in myoplasmic calcium concentration (Ca(m)) in response to P2Y receptor agonists. In contrast to UDP, activation by UTP or adenosine 5'-triphosphate (ATP) greatly increased Ca(m), which indicates upregulation of functional P2Y2 receptors at which UTP and ATP are equipotent agonists. The number of responsive cells was significantly greater for freshly dispersed SMCs from collared arteries than for controls. Perivascular infusion of UTP (100 micromol/L) within the collar significantly enhanced neointimal development. Intimas that resulted from UTP exposure were infiltrated by macrophages. Moreover, increased expression of osteopontin occurred in response to in situ application of UTP. ATP or UTP also stimulated osteopontin expression in cultured SMCs in a dose-dependent manner. Furthermore, P2Y2 antisense oligonucleotide inhibited osteopontin expression induced by UTP.

CONCLUSIONS

These findings indicate for the first time a role for the UTP/ATP receptor, P2Y2, in development of intimal hyperplasia associated with atherosclerosis and restenosis.

P2 receptor antagonist PPADS inhibits mesangial cell proliferation in experimental mesangial proliferative glomerulonephritis

BACKGROUND

Although extracellular nucleotides have been shown to confer mitogenic effects in cultured rat mesangial cells through activation of purinergic P2 receptors (P2Y receptors), thus far the in vivo relevance of these findings is unclear. Virtually all cells and in particular the dense granules of platelets contain high levels of nucleotides that are released upon cell injury or platelet aggregation. In experimental mesangial proliferative glomerulonephritis in the rat (anti-Thy1 model), mesangiolysis and glomerular platelet aggregation are followed by a pronounced mesangial cell (MC) proliferative response leading to glomerular hypercellularity. Therefore, we examined the role of extracellular nucleotides and their corresponding receptors in nucleotide-stimulated cultured mesangial cells and in inflammatory glomerular disease using the P2 receptor antagonist PPADS.

METHODS

The effects of PPADS on nucleotide- or fetal calf serum (FCS)-stimulated proliferation of cultured MC were measured by cell counting and [3H]thymidine incorporation assay. After induction of the anti-Thy1 model, rats received injections of the P2-receptor antagonist PPADS at different doses (15, 30, 60 mg/kg BW). Proliferating mesangial and non-mesangial cells, mesangial cell activation, matrix accumulation, influx of inflammatory cells, mesangiolysis, microaneurysm formation, and renal functional parameters were assessed during anti-Thy1 disease. P2Y-mRNA and protein expression was assessed using RT-PCR and real time PCR, Northern blot analysis, in situ hybridization, and immunohistochemistry.

RESULTS

In cultured mesangial cells, PPADS inhibited nucleotide, but not FCS-stimulated proliferation in a dose-dependent manner. In the anti-Thy1 model, PPADS specifically and dose-dependently reduced early (day 3), but not late (day 8), glomerular mesangial cell proliferation as well as phenotypic activation of the mesangium and slightly matrix expansion. While no consistent effect was obtained in regard to the degree of mesangiolysis, influx of inflammatory cells, proteinuria or blood pressure, PPADS treatment increased serum creatinine and urea in anti-Thy1 rats. P2Y receptor expression (P2Y2 and P2Y6) was detected in cultured MC and isolated glomeruli, and demonstrated a transient marked increase during anti-Thy1 disease.

CONCLUSION

These data strongly suggest an in vivo role for extracellular nucleotides in mediating early MC proliferation after MC injury.

Regional variation in P2 receptor expression in the rat pulmonary arterial circulation

The P2 receptors that mediate contraction of the rat isolated small (SPA, 200-500 micro m i.d.) and large (LPA, 1-1.5 mM i.d.) intrapulmonary arteries were characterized. 2 In endothelium-denuded vessels the contractile order of potency was alpha,beta-methyleneATP (alpha,beta-meATP)>>UDP=UTP=ATP=2-methylthioATP>ADP in the SPA and alpha,beta-meATP=UTP>or=UDP>2-methylthioATP, ATP>>ADP in the LPA. alpha,beta-meATP, 2-methylthioATP and ATP had significantly greater effects in the SPA than the LPA (P<0.001), but there was no difference in the potency of UTP or UDP between the vessels. 3 In the SPA, P2X1 receptor desensitisation by alpha,beta-meATP (100 microM) inhibited contractions to alpha,beta-meATP (10 nM-300 microM), but not those to UTP or UDP (100 nM-300 microM). In the LPA, prolonged exposure to alpha,beta-meATP (100 microM) did not desensitize P2X receptors. 4 Pyridoxalphosphate-6-azophenyl-2',4'-disulphonic acid (PPADS), suramin and reactive blue 2 (RB2) (30-300 microM) inhibited contractions evoked by alpha,beta-meATP. UTP and UDP were potentiated by PPADS, unaffected by RB2 and inhibited, but not abolished by suramin. 1 and 3 mM suramin produced no further inhibition, indicating suramin-resistant components in the responses to UTP and UDP. 5 Thus, both P2X and P2Y receptors mediate contraction of rat large and small intrapulmonary arteries. P2Y agonist potency and sensitivity to antagonists were similar in small and large vessels, but P2X agonists were more potent in small arteries. This indicates differential expression of P2X, but not P2Y receptors along the pulmonary arterial tree.

ATP-induced endothelium-independent enhancement of lymphatic vasomotion in guinea-pig mesentery involves P2X and P2Y receptors

1. The present study has investigated mechanisms underlying ATP-induced endothelium-independent enhancement of vasomotion in guinea-pig mesenteric lymphatic vessels. 2. Lymphatic vasomotion, vessel tone and smooth muscle [Ca(2+)](i) showed similar ATP concentration-response curves. 3. ATP, at 0.1 mM, caused a biphasic increase in tonic [Ca(2+)](i) and superimposed vasomotion-associated Ca(2+) transients. All ATP-induced [Ca(2+)](i) changes were abolished by incubating the smooth muscle with suramin (0.1 mM). 4. alpha,beta-MeATP (0.1 mM) and UTP (0.1 mM) caused similar changes in [Ca(2+)](i) but the responses to these agonists were smaller than to ATP. 5. The actions of alpha,beta-MeATP (0.1 mM) were inhibited by suramin (0.1 mM) and PPADS (30 micro M) but not by reactive blue 2 (30 micro M). 6. In the presence of alpha,beta-MeATP (0.1 mM), the increases in tonic [Ca(2+)](i) and vasomotion-associated Ca(2+) transients induced by ATP (0.1 mM) were inhibited by U73122 (5 micro M), CPA (20 micro M) and heparin, whereas U73343 (5 micro M) and pre-treatment with PTx (100 ng ml(-1)) had no significant effects. 7. Depletion of the intracellular stores with CPA (20 micro M) caused an increase in [Ca(2+)](i), which was not blocked by desensitization of P(2X) receptors with alpha,beta-MeATP. 8. The data indicate that ATP, at relatively high concentrations increases lymphatic smooth muscle [Ca(2+)](i) and vasomotion through activation of P(2X1) and P(2Y2) purinoceptors present on lymphatic smooth muscle. The increase in [Ca(2+)](i) is likely to result from Ca(2+) release from inositol-1,4,5-trisphosphate-sensitive stores as well as Ca(2+) influx through store-operated channels and P(2X)-gated channels.