Release Of Adenine Nucleotides Research Articles

Temperature limits for storage of extended boar semen from the perspective of the sperm's energy status.

The optimum storage temperature for liquid-preserved boar semen has been empirically determined to be between 15 and 20°C. Lower temperatures provide an advantage to inhibit bacterial growth, but are regarded as critical due to the high sensitivity of boar spermatozoa to chilling injury. Higher storage temperatures are supposed to induce energy deficiency due to an insufficient depression of metabolic cell activity. However, experimental evidence for alterations of the sperm's energy status in relation to storage temperature and duration is missing. Therefore, we aimed to revisit the upper and lower storage temperature limits for liquid-preserved boar semen from the perspective of the sperm's energy metabolism. Ejaculates (n = 7 boars) were cooled down in Beltsville Thawing Solution (BTS) to 25, 17, 10, or 5°C and stored for up to 120 h. ATP and adenylate energy charge (EC) levels were assessed at storage temperature (24, 72, and 120 h storage) and after subsequent re-warming (38°C). Sperm quality and energy status remained at a stable level in samples stored at 25 and 17°C. Chilling to and storage at 10 or 5°C in BTS provoked cold shock in a subset of sperm as shown by a loss in viability and motility (P < 0.05), which was accompanied by a significant release of adenine nucleotides into the semen extender. Prolonged storage for 120 h resulted in significantly lower mean ATP concentrations in viable spermatozoa at 5 or 10°C compared to 17°C (P < 0.05). Cluster analysis revealed that the main sperm subpopulation, i.e., sperm with moderate speed and linearity, decreased from 50 to 30% (P < 0.05) in favor of slow-moving spermatozoa (5°C) or spermatozoa with a hyperactivation-like motility pattern (10°C). The results point to a sublethal imbalance in available ATP in a subset of the surviving sperm population, rather than a general decrease in available ATP in all spermatozoa. In conclusion, storing diluted boar semen at a stable temperature between 17 and 25°C is a safe procedure concerning the spermatozoa's energy status. Future concepts for hypothermic boar semen preservation below 17°C require measures which ameliorate the imbalanced energy status in viable spermatozoa.

Pannexin Channel Regulation of Cell Migration: Focus on Immune Cells.

The role of Pannexin (PANX) channels during collective and single cell migration is increasingly recognized. Amongst many functions that are relevant to cell migration, here we focus on the role of PANX-mediated adenine nucleotide release and associated autocrine and paracrine signaling. We also summarize the contribution of PANXs with the cytoskeleton, which is also key regulator of cell migration. PANXs, as mechanosensitive ATP releasing channels, provide a unique link between cell migration and purinergic communication. The functional association with several purinergic receptors, together with a plethora of signals that modulate their opening, allows PANX channels to integrate physical and chemical cues during inflammation. Ubiquitously expressed in almost all immune cells, PANX1 opening has been reported in different immunological contexts. Immune activation is the epitome coordination between cell communication and migration, as leukocytes (i.e., T cells, dendritic cells) exchange information while migrating towards the injury site. In the current review, we summarized the contribution of PANX channels during immune cell migration and recruitment; although we also compile the available evidence for non-immune cells (including fibroblasts, keratinocytes, astrocytes, and cancer cells). Finally, we discuss the current evidence of PANX1 and PANX3 channels as a both positive and/or negative regulator in different inflammatory conditions, proposing a general mechanism of these channels contribution during cell migration.

Smooth-talking T cells leave asthma breathless

The plasma membrane channel PANX1 mediates release of bio-active adenine nucleotides; however, its function in immune cells is unknown. In this issue of Immunity, Medina etal. show that PANX1 mediates adenosine-dependent communication between regulatory and effector CD4+ Tcells during allergic airway inflammation.

Adaptation to inflammatory acidity through neutrophil-derived adenosine regulation of SLC26A3.

Acute intestinal inflammation includes the early accumulation of neutrophils (PMN). Based on recent evidence that PMN infiltration “imprints” changes in the local tissue environment through local oxygen depletion and the release of adenine nucleotides, we hypothesized that the interaction between transmigrating PMN and intestinal epithelial cells (IECs) results in inflammatory acidification of the tissue. Using newly developed tools, we revealed that active PMN transepithelial migration (TEM) significantly acidifies the local microenvironment, a decrease of nearly 2 pH units. Using unbiased approaches, we sought to define acid-adaptive pathways elicited by PMN TEM. Given the significant amount of adenosine (Ado) generated during PMN TEM, we profiled the influence of Ado on IECs gene expression by microarray and identified the induction of SLC26A3, the major apical Cl−/HCO3− exchanger in IECs. Utilizing loss- and gain-of-function approaches, as well as murine and human colonoids, we demonstrate that Ado-induced SLC26A3 promotes an adaptive IECs phenotype that buffers local pH during active inflammation. Extending these studies, chronic murine colitis models were used to demonstrate that SLC26A3 expression rebounds during chronic DSS-induced inflammation. In conclusion, Ado signaling during PMN TEM induces an adaptive tissue response to inflammatory acidification through the induction of SLC26A3 expression, thereby promoting pH homeostasis.

An Intermediary Role of Adenine Nucleotides on Free Fatty Acids-Induced Hyperglycemia in Obese Mice.

Increased plasma free fatty acids (FFA) level plays a central role in the development of type 2 diabetes. Our previous studies have shown that plasma 5′-adenosine monophosphate (5′-AMP) elevates and acts as a potential upstream regulator of hyperglycemia in diabetic db/db mice. The relationship between FFA and plasma adenosine nucleotides in type 2 diabetes remains unclear. Here we found that plasma 5′-AMP level was also increased in diabetic mice induced by a high-fat diet and streptozotocin (HFD-STZ), as observed in diabetic db/db mice. The metabolites of adenosine nucleotides in plasma were increased in obese mice compared to lean mice. An acute oil gavage to lean mice increased both FFA and plasma purine metabolites, accompanying with glucose intolerance. 5′-AMP administration resulted in an increase in dose-dependent purine metabolites and different levels of glucose intolerance. FFA induced a release of adenine nucleotides from cultural human umbilical vein endothelial cells (HUVECs) prior to induction of their apoptosis. FFA also reduced red blood cells (RBCs) resistance to reactive oxygen species (ROS), leading to hemolysis, thereby increasing plasma nucleotides. Our results suggest that plasma adenine nucleotides play an intermediary role in FFA-induced glucose intolerance and hyperglycemia in obese mice.

Adenosine A2A receptors in neuronal outgrowth: a target for nerve regeneration?

Adenosine A2A receptors in neuronal outgrowth: a target for nerve regeneration?

Purinergic signaling in scarring.

Adenosine (ADO) and nucleotides such as ATP, ADP, and uridine 5'-triphosphate (UTP), among others, may serve as extracellular signaling molecules. These mediators activate specific cell-surface receptors-namely, purinergic 1 and 2 (P1 and P2)-to modulate crucial pathophysiological responses. Regulation of this process is maintained by nucleoside and nucleotide transporters, as well as the ectonucleotidases ectonucleoside triphosphate diphosphohydrolase [ENTPD; cluster of differentiation (CD)39] and ecto-5'-nucleotidase (5'-NT; CD73), among others. Cells involved in tissue repair, healing, and scarring respond to both ADO and ATP. Our recent investigations have shown that modulation of purinergic signaling regulates matrix deposition during tissue repair and fibrosis in several organs. Cells release adenine nucleotides into the extracellular space, where these mediators are converted by CD39 and CD73 into ADO, which is anti-inflammatory in the short term but may also promote dermal, heart, liver, and lung fibrosis with repetitive signaling under defined circumstances. Extracellular ATP stimulates cardiac fibroblast proliferation, lung inflammation, and fibrosis. P2Y2 (UTP/ATP) and P2Y6 [ADP/UTP/uridine 5'-diphosphate (UDP)] have been shown to have profibrotic effects, as well. Modulation of purinergic signaling represents a novel approach to preventing or diminishing fibrosis. We provide an overview of the current understanding of purinergic signaling in scarring and discuss its potential to prevent or decrease fibrosis.

Deficits in endogenous adenosine formation by ecto-5'-nucleotidase/CD73 impair neuromuscular transmission and immune competence in experimental autoimmune myasthenia gravis.

AMP dephosphorylation via ecto-5′-nucleotidase/CD73 is the rate limiting step to generate extracellular adenosine (ADO) from released adenine nucleotides. ADO, via A2A receptors (A2ARs), is a potent modulator of neuromuscular and immunological responses. The pivotal role of ecto-5′-nucleotidase/CD73, in controlling extracellular ADO formation, prompted us to investigate its role in a rat model of experimental autoimmune myasthenia gravis (EAMG). Results show that CD4+CD25+FoxP3+ regulatory T cells express lower amounts of ecto-5′-nucleotidase/CD73 as compared to controls. Reduction of endogenous ADO formation might explain why proliferation of CD4+ T cells failed upon blocking A2A receptors activation with ZM241385 or adenosine deaminase in EAMG animals. Deficits in ADO also contribute to neuromuscular transmission failure in EAMG rats. Rehabilitation of A2AR-mediated immune suppression and facilitation of transmitter release were observed by incubating the cells with the nucleoside precursor, AMP. These findings, together with the characteristic increase in serum adenosine deaminase activity of MG patients, strengthen our hypothesis that the adenosinergic pathway may be dysfunctional in EAMG. Given that endogenous ADO formation is balanced by ecto-5′-nucleotidase/CD73 activity and that A2ARs exert a dual role to restore use-dependent neurocompetence and immune suppression in myasthenics, we hypothesize that stimulation of the two mechanisms may have therapeutic potential in MG.

Adenosine as an endogenous immunoregulator in cancer pathogenesis: where to go?

Cancer is a chronic disease and its pathogenesis is well correlated with infection and inflammation. Adenosine is a purine nucleoside, which is produced under metabolic stress like hypoxic conditions. Acute or chronic inflammatory conditions lead to the release of precursor adenine nucleotides (adenosine triphosphate (ATP), adenosien diphosphate (ADP) and adenosine monophosphate (AMP)) from cells, which are extracellularly catabolized into adenosine by extracellular ectonucleotidases, i.e., CD39 or nucleoside triphosphate dephosphorylase (NTPD) and CD73 or 5'-ectonucleotidase. It is now well-known that adenosine is secreted by cancer as well as immune cells during tumor pathogenesis under metabolic stress or hypoxia. Once adenosine is released into the extracellular environment, it exerts various immunomodulatory effects via adenosine receptors (A1, A2A, A2B, and A3) expressed on various immune cells (i.e., macrophages, myeloid-derived suppressor cells (MDSCs), natural killer (NK) cells, dendritic cells (DCs), T cells, regulatory T cell (Tregs), etc.), which play very important roles in the pathogenesis of cancer. This review is intended to summarize the role of inflammation and adenosine in the immunopathogenesis of tumor along with regulation of tumor-specific immune response and its modulation as an adjunct approach to tumor immunotherapy.

Bradykinin activation of fibroblasts of the rat subcutaneous tissue triggers the release of ATP and P2 purinoceptors activation

BACKGROUND. Pain related to musculoskeletal system is increasingly common and purines, acting through distinct signaling pathways, are described to be involved in nociception (Schleip & Klingler, 2008). Considering that fibroblasts from subcutaneous connective tissue can release adenine or uridine nucleotides, triggering intracellular Ca 2+ waves in response to stressful conditions, these cells may play a key role in the propagation/amplification of signals to primary afferent neurons (Furuya et al., 2005). Thus, we decided to investigate the involvement of purinoceptors on bradykinin (BK)-induced activation of fibroblasts of the rat subcutaneous tissue. METHODS. Experiments were performed in the first subculture of fibroblasts isolated from rat subcutaneous connective tissue. Intracellular ATP release was inferred from destaining of cells loaded with quinacrine (an ATP-binding intracellular fluorescent dye) by confocal microscopy (Orriss et al., 2009). Intracellular Ca 2+ oscillations were monitored using a microplate reader after loading the cells with the fluorescent Ca 2+ dye, Fluo-4NW. The expression of P2 purinoceptors on cultured fibroblasts of the rat subcutaneous tissues was evaluated by immunofluorescence confocal microscopy. RESULTS. Exposure to BK (30 μM) significantly enhanced fluorescence destaining of cultured fibroblasts loaded with quinacrine, suggesting that fibroblasts release intracellular ATP when stimulated with BK. In the presence of brefeldin A, which is a potent inhibitor of vesicular trafficking and secretion, BK (30 μM) was unable to increase intracellular Ca 2+ accumulation. Moreover, we observed a decrease of the BK-induced Ca 2+ response in the presence of the Cx36 and Cx50 inhibitor, mefloquine, and of the selective pannexin-1 inhibitor, 10 Panx. The intracellular Ca 2+ accumulation induced by BK was also partially attenuated by apyrase, an enzyme that hydrolyses ATP and ADP directly to AMP. Interestingly, the ecto-NTPDase inhibitor, POM-1, which prevents sequential dephosphorylation of ATP to ADP leading to ATP accumulation and ADP depletion, also prevented BK-induced intracellular Ca 2+ increase. These results point towards the participation of ADP generated from the extracellular catabolism of released ATP on BKinduced fibroblast Ca 2+ rises. Fibroblast Ca 2+ oscillations caused by BK were partially attenuated in the presence of the selective P2Y1 receptor antagonist, MRS 2179, but not upon the selective blockade of P2Y12 and P2Y13 receptors, respectively with AR-C66096 and MRS 2211. The expression of P2Y1 receptors on cultured fibroblasts from rat the subcutaneous tissue was confirmed by immunofluorescence confocal microscopy. CONCLUSIONS. Data suggest that BK-evoked responses may be partially mediated by endogenous released adenine nucleotides via a mechanism involving hemichannels and vesicle exocytosis. Extracellular hydrolysis of released ATP into ADP may facilitate the inflammatory responses of BK through the activation of P2Y1 receptors. Understanding how fibroblasts of the subcutaneous tissue trigger the release of signal amplification molecules, such as adenine nucleotides, which may ultimately contribute to activate neighboring cells, including sensory neurons, enlightens the hypothesis that fibroblast may be a novel target for therapeutic intervention in chronic painful conditions.

Laminar Shear Stress Up‐regulates Endothelial CD73 Expression by Activating Calmodulin‐dependent Kinase Kinase

Endothelial cell (EC) surface CD73, ecto‐5′ nucleotidase, extracellularly metabolizes AMP to adenosine, a potent anti‐inflammatory molecule. Since athero‐protective high laminar shear stress (LS) rises intracellular calcium levels and induces the release of adenine nucleotides in ECs, we hypothesized that LS increases CD73 expression by activating calmodulin‐dependent kinase kinase (CaMKK), leading to the extracellular production of adenosine in ECs.Cultured human coronary artery ECs were subjected to static, LS (15 dyne/cm2), or oscillatory shear (OS; ± 5 dyne/cm2) condition for 24 hours. Real‐time PCR showed that LS increased CD73 mRNA expression (2.1±0.3‐fold increase vs. static condition, p&lt;0.05, n=10–17), whereas OS unchanged the mRNA expression (0.9±0.2 fold, p=ns, n=6). STO‐609 (a CaMKK inhibitor, 10μg/ml) suppressed LS‐induced increase in CD73 mRNA expression (1.1±0.2 fold, n=5). In contrast, U‐73122 (a phospholipase C inhibitor, 1μM) and KN‐62 (a calcium/calmodulin‐dependent kinase inhibitor, 10 μM) had no inhibitory effect (2.7±0.5 fold, n=3 and 2.1±0.3, n=8). HPLC analysis revealed that LS resulted in the accumulation of adenosine in the conditioned medium.These results indicate that LS elicits the generation of extracellular adenosine from ECs by upregulating CD73 expression via activating CaMKK. Thus, CD73 might contribute to the athero‐protective effects of LS in ECs.

Response of blood platelets to β-glucan from Saccharomyces cerevisiae

The effects of the β-D-glucan, a polysaccharide derived from the yeast cell walls of species such as Saccharomyces cerevisiae, on blood platelets activation induced by physiological agonists (thrombin, ADP, collagen) in vitro were studied. The aim of our study was to assess in vitro if β-glucan, a naturally strong biological response modifier, may modify platelet activation, i.e. platelet aggregation and degranulation (release of proteins and adenine nucleotides) induced by thrombin, ADP and collagen. Cytochrome c reduction method was used to test the ability of β-glucan to change superoxide anion generation in platelets. Moreover, we determined also its effect on enzymatic arachidonic acid cascade. The obtained results indicate that β-glucan has the inhibitory effects on platelet aggregation and secretion. β-glucan distinctly reduced the arachidonic acid pathway and superoxide anion radical generation in platelets stimulated by biological agonists. The results of the present study suggest that β-glucan from Saccharomyces cerevisiae has antiplatelet and antioxidative activities, and therefore may be beneficial in the prevention of the excessive blood platelet activation–related diseases, such as cardiovascular or inflammatory diseases.

α1-acid glycoprotein (AGP)-induced platelet shape change involves the Rho/Rho kinase signalling pathway

alpha(1)-acid glycoprotein (AGP) is an acute-phase protein that contributes to inflammation processes. The role of AGP in platelet activation and thrombosis is, however, largely unknown. Therefore, we thoroughly investigated the effects of AGP on human platelets. Platelets were isolated from healthy volunteers and subsequently exposed to AGP. Platelet responses were monitored as change in light transmission, intracellular calcium concentration, light microscopy and protein phosphorylation by Western blot. We found that AGP induced platelet shape change independently of a second release of adenine nucleotides or thromboxane A(2), and that effect was abolished by endothelium-derived platelet inhibitors such as nitric oxide (NO) and adenosine. Furthermore, AGP triggered a minor calcium response and a pronounced Rho/Rho-kinase-dependent increase in Thr696 phosphorylation of myosin phosphatase target subunit 1 (MYPT1). Moreover, the Rho/Rho-kinase inhibitor Y-27632 significantly decreased the AGP-induced shape change. The results also showed that the AGP-elicited shape change was antagonised by pretreatment with low doses of collagen and thrombospondin-1. Our results describe a novel mechanism by which AGP stimulates platelet shape change via activation of the Rho/Rho-kinase signalling pathway. Physiological important platelet inhibitors, such as NO, completely counterbalance the effect of AGP. Hence, the present study indicates that AGP directly contributes to platelet activation, which in turn might have an impact in physiological haemostasis and/or pathological thrombosis.

Similarities between UDP-Glucose and Adenine Nucleotide Release in Yeast: Involvement of the Secretory Pathway

ADVERTISEMENT RETURN TO ISSUEPREVAddition/CorrectionORIGINAL ARTICLEThis notice is a correctionSimilarities between UDP-Glucose and Adenine Nucleotide Release in Yeast: Involvement of the Secretory PathwayCharles R. Esther, Jr.*, Juliana I. Sesma, Henrik G. Dohlman, Addison D. Ault, Marién L. Clas, Eduardo R. Lazarowski, and Richard C. BoucherCite this: Biochemistry 2008, 47, 44, 11693Publication Date (Web):October 7, 2008Publication History Received29 September 2008Published online7 October 2008Published inissue 4 November 2008https://doi.org/10.1021/bi8018477Copyright © 2008 American Chemical SocietyRIGHTS & PERMISSIONSArticle Views237Altmetric-Citations-LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InReddit PDF (14 KB) Get e-AlertsSUBJECTS:Adenine,Fungi,Monomers Get e-Alerts

Similarities between UDP-Glucose and Adenine Nucleotide Release in Yeast: Involvement of the Secretory Pathway

Extracellular UDP-glucose is a natural purinergic receptor agonist, but its mechanisms of cellular release remain unclear. We studied these mechanisms in Saccharomyces cerevisiae, a simple model organism that releases ATP, another purinergic agonist. Similar to ATP, UDP-glucose was released by S. cerevisiae at a rate that was linear over time. However, unlike ATP release, UDP-glucose release was not dependent on glucose stimulation. This discrepancy was resolved by demonstrating the apparent glucose stimulation of ATP release reflected glucose-dependent changes in the intracellular pattern of adenine nucleotides, with AMP release dominating in the absence of glucose. Indeed, total adenine nucleotide release, like UDP-glucose release, did not vary with glucose concentration over the short term. The genetic basis of UDP-glucose release was explored through analysis of deletion mutants, aided by development of a novel bioassay for UDP-glucose based on signaling through heterologously expressed human P2Y 14 receptors. Using this assay, an elevated rate of UDP-glucose release was demonstrated in mutants lacking the putative Golgi nucleotide sugar transporter YMD8. An increased rate of UDP-glucose release in ymd8Delta was reduced by deletion of the YEA4 UDP- N-acetylglucosamine or the HUT1 UDP-galactose transporters, and overexpression of YEA4 or HUT1 increased the rate of UDP-glucose release. These findings suggest an exocytotic release mechanism similar to that of ATP, a conclusion supported by decreased rates of ATP, AMP, and UDP-glucose release in response to the secretory inhibitor Brefeldin A. These studies demonstrate the involvement of the secretory pathway in nucleotide and nucleotide sugar efflux in yeast and offer a powerful model system for further investigation.

Similarities between UDP-Glucose and Adenine Nucleotide Release in Yeast: Involvement of the Secretory Pathway

Similarities between UDP-Glucose and Adenine Nucleotide Release in Yeast: Involvement of the Secretory Pathway

The antiinflammatory mechanism of methotrexate depends on extracellular conversion of adenine nucleotides to adenosine by ecto‐5′‐nucleotidase: Findings in a study of ecto‐5′‐nucleotidase gene–deficient mice

Evidence from in vitro, in vivo, and clinical studies indicates that adenosine mediates, at least in part, the antiinflammatory effects of methotrexate (MTX), although the biochemical events involved have not been fully elucidated. This study was undertaken to investigate whether MTX exerts antiinflammatory effects in mice that lack ecto-5'-nucleotidase (ecto-5'-NT) (CD73) and are unable to convert AMP to adenosine extracellularly, in order to determine whether adenosine is generated intracellularly and transported into the extracellular space or is generated from the extracellular dephosphorylation of AMP to adenosine. Male CD73 gene-deficient mice and age-matched wild-type mice received intraperitoneal injections of saline or MTX (1 mg/kg/week) for 5 weeks. Air pouches were induced on the back by subcutaneous injection of air; 6 days later, inflammation was induced by injection of carrageenan. Fewer leukocytes, but higher levels of tumor necrosis factor alpha (TNFalpha), accumulated in the air pouches of vehicle-treated CD73-deficient mice compared with those of wild-type mice. As expected, MTX treatment reduced the number of leukocytes and TNFalpha levels in the exudates and increased exudate adenosine concentrations in wild-type mice. In contrast, MTX did not reduce exudate leukocyte counts or TNFalpha levels or increase exudate adenosine levels in CD73-deficient mice. These results demonstrate that the antiinflammatory actions of MTX are mediated, at least in part, by increased release of adenine nucleotides that are hydrolyzed extracellularly to adenosine via an ecto-5'-NT-dependent pathway.

Gene expression for enzymes and transporters involved in regulating adenosine and inosine levels in rat forebrain neurons, astrocytes and C6 glioma cells

In brain, levels of adenosine increase up to 100-fold during cerebral ischemia. Based on in vitro studies, both astrocytes and neurons contribute to this adenosine release. Neurons release adenosine per se whereas astrocytes release adenine nucleotides that are metabolized to adenosine extracellularly. In contrast, inosine is released from both cell types via a nucleoside transporter. C6 glioma cells, which are derived from astrocytes, release inosine but not adenosine. The present study investigated the relative expression of purine metabolizing enzymes and transporters in neurons, astrocytes and C6 glioma cells by real-time PCR analysis. In agreement with the extracellular formation of adenosine and intracellular formation of inosine by astrocytes, the present study showed high expression of ecto 5'-nucleotidase and AMP deaminase type 3 in astrocytes. The lack of adenosine release from C6 glioma cells was consistent with the absence of expression of the AMP-preferring cytosolic 5'-nucleotidase in these cells. The predominance of nitrobenzylthioinosine (NBMPR) insensitive equilibrative nucleoside transport (ENT2) in all three cell types was consistent with the greater activity of this isoform in comparison to NBMPR-sensitive ENT1 in these rat cells. Thus, cell type differences in adenosine formation and release are primarily a function of differences in expression of purinergic enzymes and transporters.

Excitatory P2‐receptors at sympathetic axon terminals: role in temperature control of cutaneous blood flow

The mechanisms underlying the reduction in cutaneous blood flow in response to cooling are only partially understood. A study published in this issue of the British Journal of Pharmacology now provides evidence for the involvement of excitatory P2-receptors located at sympathetic axon terminals in the cooling-induced vasoconstriction in the skin. Cooling appears to cause the release of adenine nucleotides followed by the activation of excitatory presynaptic P2-receptors at noradrenergic axon terminals. Activation of these excitatory P2-receptors induces the release of noradrenaline, which subsequently causes constriction of blood vessels in the skin by action on smooth muscle alpha(1)- and alpha(2)-adrenoceptors. The commentary discusses the implication of the results and remaining questions.

Ecto-5′-Nucleotidase (CD73)-Mediated Adenosine Production Is Tissue Protective in a Model of Bleomycin-Induced Lung Injury

Adenosine signaling has diverse actions on inflammation and tissue injury. Levels of adenosine are rapidly elevated in response to tissue injury; however, the mechanisms responsible for adenosine production in response to injury are not well understood. In this study, we found that adenosine levels are elevated in the lungs of mice injured by the drug bleomycin. In addition, increased activity of ecto-5'-nucleotidase (CD73) was found in the lungs in conjunction with adenosine elevations. To determine the contribution of CD73 to the generation of adenosine in the lung, CD73(-/-) mice were subjected to bleomycin challenges. Results demonstrated that CD73(-/-) mice challenged with bleomycin no longer accumulated adenosine in their lungs, suggesting that the primary means of adenosine production following bleomycin injury resulted from the release and subsequent dephosphorylation of adenine nucleotides. CD73(-/-) mice challenged with bleomycin exhibited enhanced pulmonary inflammation and fibrosis as well as exaggerated expression of proinflammatory and profibrotic mediators in the lung. Intranasal instillations of exogenous nucleotidase restored the ability of lungs of CD73(-/-) mice to accumulate adenosine following bleomycin challenge. Furthermore, these treatments were associated with a decrease in pulmonary inflammation and fibrosis. CD73(+/+) animals challenged with bleomycin and supplemented with exogenous nucleotidase also exhibited reduced inflammation. Together, these findings suggest that CD73-dependent adenosine production contributes to anti-inflammatory pathways in bleomycin-induced lung injury.