Extracellular ATP and cell signalling

Analysis of Extracellular ATP Distribution in the Intervertebral Disc

Progressive loss of proteoglycans (PGs) is the major biochemical change during intervertebral disc (IVD) degeneration. Adenosine triphosphate (ATP) as the primary energy source is not only critical for cell survival but also serves as a building block in PG synthesis. Extracellular ATP can mediate a variety of physiological functions and was shown to promote extracellular matrix (ECM) production in the IVD. Therefore, the objective of this study was to develop a 3D finite element model to predict extracellular ATP distribution in the IVD and evaluate the impact of degeneration on extracellular ATP distribution. A novel 3D finite element model of the IVD was developed by incorporating experimental measurements of ATP metabolism and ATP-PG binding kinetics into the mechano-electrochemical mixture theory. The new model was validated by experimental data of porcine IVD, and then used to analyze the extracellular distribution of ATP in human IVDs. Extracellular ATP was shown to bind specifically with PGs in IVD ECM. It was found that annulus fibrosus cells hydrolyze ATP faster than that of nucleus pulposus (NP) cells whereas NP cells exhibited a higher ATP release. The distribution of extracellular ATP in a porcine model was consistent with experimental data in our previous study. The predictions from a human IVD model showed a high accumulation of extracellular ATP in the NP region, whereas the extracellular ATP level was reduced with tissue degeneration. This study provides an understanding of extracellular ATP metabolism and its potential biological influences on the IVD via purinergic signaling.

DNA Logic Circuits for Cancer Theranostics

Cancer diagnosis and therapeutics (theranostics) based on the tumor microenvironment (TME) and biomarkers has been an emerging approach for precision medicine. DNA nanotechnology dynamically controls the self-assembly of DNA molecules at the nanometer scale to construct intelligent DNA chemical reaction systems. The DNA logic circuit is a particularly emerging approach for computing within the DNA chemical systems. DNA logic circuits can sensitively respond to tumor-specific markers and the TME through logic operations and signal amplification, to generate detectable signals or to release anti-cancer agents. In this review, the fundamental concepts of DNA logic circuits are clarified, the basic modules in the circuit are summarized, and how this advanced nano-assembly circuit responds to tumor-related molecules, how to perform logic operations, to realize signal amplification, and selectively release drugs through discussing over 30 application examples, are demonstrated. This review shows that DNA logic circuits have powerful logic judgment and signal amplification functions in improving the specificity and sensitivity of cancer diagnosis and making cancer treatment controllable. In the future, researchers are expected to overcome the existing shortcomings of DNA logic circuits and design smarter DNA devices with better biocompatibility and stability, which will further promote the development of cancer theranostics.

ATP-Responsive Liposomes via Screening of Lipid Switches Designed to Undergo Conformational Changes upon Binding Phosphorylated Metabolites

Liposomal delivery vehicles can dramatically enhance drug transport. However, their clinical application requires enhanced control over content release at diseased sites. For this reason, triggered release strategies have been explored, although a limited toolbox of stimuli has thus far been developed. Here, we report a novel strategy for stimuli-responsive liposomes that release encapsulated contents in the presence of phosphorylated small molecules. Our formulation efforts culminated in selective cargo release driven by ATP, a universal energy source that is upregulated in diseases such as cancer. Specifically, we developed lipid switches 1a-b bearing two ZnDPA units designed to undergo substantial conformational changes upon ATP binding, thereby disrupting membrane packing and triggering the release of encapsulated contents. Dye leakage assays using the hydrophobic dye Nile red validated that ATP-driven release was selective over 11 similar phosphorylated metabolites, and release of the hydrophilic dye calcein was also achieved. Multiple alternative lipid switch structures were synthesized and studied (1c-d and 2), which provided insights into the structural features that render 1a-b selective toward ATP-driven release. Importantly, analysis of cellular delivery using fluorescence microscopy in conjunction with pharmacological ATP manipulation showed that liposome delivery was specific, as it increased upon intracellular ATP accumulation, and was inhibited by ATP downregulation. Our new approach shows strong prospects for enhancing the selectivity of release and payload delivery to diseased cells driven by metabolites such as ATP, providing an exciting new paradigm for controlled release.

Efficient Stable Cell Line Generation of Survivin as an In Vitro Model for Specific Functional Analysis in Apoptosis and Drug Screening

Recognizing proteins that lead to a decreased efficiency of treatment in cancer cells constitutes a main goal for biomedical and biotechnological research and applications. Establishing recombinant cells that overexpress a gene of interest stably is important for treatment studies and drug/compound screening. Survivin is an anti-apoptotic protein which can be a potential candidate for regulating cell death and survival. To investigate the association between survivin increment and apoptosis rate, survivin-reconstituted HEK (HEK-S) cell was developed as in vitro model. RT-PCR and Western blot demonstrated that survivin was constitutively overexpressed in HEK-S cells. Both morphological observation and survival assay showed that HEK-S cells were significantly resistant to apoptotic stimuli. Survivin overexpression led to a decrease in caspase 3/7 activity, whereas YM155 led to a corresponding enhance of caspase activity. ROS level was decreased but ATP content increased in HEK-S cells. Also, HEK-S showed less red- fluorescence and reduced cell proliferation compared to HEK after stimulation. Resistance to laser irradiation was clearly visible as compared with control. Moreover, scratching analysis demonstrated the ability of survivin to cause neighboring cells to increase resistance to drug, whereas YM155 enhanced apoptotic rate and declined invasion in HEK-S cells.

Effects of doxorubicin and docetaxel on susceptibility to apoptosis in high expression level of survivin in HEK and HEK-S cell lines as in vitro models

A major problem in the cancer treatment is the inherent resistance to chemotherapy. Identifying proteins that, once introduced in cancer cells, lead to a decreased efficiency of treatment outcome constitutes a major goal for biomedical research and applications. Survivin is a protein of IAPs family which its high expression can be a potential candidate for regulating cell death and survival in cancer therapy. To investigate the association of survivin increment and resistance to drug, survivin-reconstituted HEK (HEK-S) and HEK cells were used as in vitro models for the doxorubicin and docetaxel cellular response. Both morphological observation and survival assay exhibited that survivin reconstitution cells were significantly resistant to apoptotic stimuli by both drugs. It was observed that survivin overexpression has led to a decrease in caspase 3/7 activity and ROS level of cells but an increase in ATP content. Also, survivin-reconstituted cell displayed less red fluorescence compared to control after stimulation by drugs. Moreover, wound healing assay showed the ability of survivin to cause neighbouring cells to increase resistance to induction. These findings demonstrated survivin could be a potential target that can be inhibited the function of different drugs with various mechanisms in chemotherapy.

PI3K activation prevents Aβ42-induced synapse loss and favors insoluble amyloid deposit formation

Excess of Aβ42 peptide is considered a hallmark of the disease. Here we express the human Aβ42 peptide to assay the neuroprotective effects of PI3K in adult Drosophila melanogaster. The neuronal expression of the human peptide elicits progressive toxicity in the adult fly. The pathological traits include reduced axonal transport, synapse loss, defective climbing ability and olfactory perception, as well as lifespan reduction. The Aβ42-dependent synapse decay does not involve transcriptional changes in the core synaptic protein encoding genes bruchpilot, liprin and synaptobrevin. All toxicity features, however, are suppressed by the coexpression of PI3K. Moreover, PI3K activation induces a significant increase of 6E10 and thioflavin-positive amyloid deposits. Mechanistically, we suggest that Aβ42-Ser26 could be a candidate residue for direct or indirect phosphorylation by PI3K. Along with these in vivo experiments, we further analyze Aβ42 toxicity and its suppression by PI3K activation in in vitro assays with SH-SY5Y human neuroblastoma cell cultures, where Aβ42 aggregation into large insoluble deposits is reproduced. Finally, we show that the Aβ42 toxicity syndrome includes the transcriptional shut down of PI3K expression. Taken together, these results uncover a potential novel pharmacological strategy against this disease through the restoration of PI3K activity.

Extracellular phosphorylation and phosphorylated proteins: not just curiosities but physiologically important

Mining of the literature and high-throughput mass spectrometry data from both healthy and diseased tissues and from body fluids reveals evidence that various extracellular proteins can exist in phosphorylated states. Extracellular kinases and phosphatases (ectokinases and ectophosphatases) are active in extracellular spaces during times of sufficiently high concentrations of adenosine triphosphate. There is evidence for a role of extracellular phosphorylation in various physiological functions, including blood coagulation, immune cell activation, and the formation of neuronal networks. Ectokinase activity is increased in some diseases, including cancer, Alzheimer's disease, and some microbial infections. We summarize the literature supporting the physiological and pathological roles of extracellularly localized protein kinases, protein phosphatases, and phosphorylated proteins and provide an analysis of the available mass spectrometry data to annotate potential extracellular phosphorylated proteins.

Ultrasound-guided continuous infraclavicular brachial plexus block using bupivacaine alone or combined with adenosine for pain control in upper limb surgery

Introduction:

The infraclavicular brachial plexus block (ICB) is designed to deposit anesthetic high in the plexus, achieving anesthesia of the hand, forearm, elbow, and distal arm. Adenosine is a metabolic intermediate that is involved in nearly all aspects of cell function, including neurotransmission and signal transduction.This study was aimed to show whether addition of adenosine to bupivacaine in ultrasound-guided ICB had an analgesic effect.

Methods:

Sixty adult patients were divided into two equal groups, each group included 30 patients. Group I received infraclavicular bupivacaine 0.325% in a volume of 30 ml. Group II received 30 ml of 0.325% bupivacaine + 12 mg adenosine. The block was maintained with an infusion of 10 ml/h. The following parameters were assessed: Success rate, time of the sensory onset, motor block, visual analog scale (VAS), and amount of i.v. pethidine needed.

Results:

This study showed an analgesic effect of infraclavicular adenosine as evidenced by a statistically significant shorter mean time of onset of the sensory block (16 vs. 20 min, P < 0.05), lower mean VAS score over 48 h (1.7 vs. 2.7, P < 0.05), longer mean time of first parenteral analgesic requirement (299 vs. 255 min, P < 0.05), and lower mean total dose of pethidine needed over 48 h after surgery (25.5 vs. 56.6 mg, P <0.05). All patients got successful infraclavicular block and recovered uneventfully without any sensory or motor deficit.

Conclusion:

Adenosine may provide valuable addition to the therapeutic options in anesthesia and pain management. Further research is required to figure out its exact role

Some aspects of purinergic signaling in the ventricular system of porcine brain

BACKGROUND

Numerous signaling pathways function in the brain ventricular system, including the most important - GABAergic, glutaminergic and dopaminergic signaling. Purinergic signalization system - comprising nucleotide receptors, nucleotidases, ATP and adenosine and their degradation products - are also present in the brain. However, the precise role of nucleotide signalling pathway in the ventricular system has been not elucidated so far. The aim of our research was the identification of all three elements of purinergic signaling pathway in the porcine brain ventricular system.

RESULTS

Besides nucleotide receptors on the ependymocytes surface, we studied purines and pyrimidines in the CSF, including mechanisms of nucleotide signaling in the swine model (Sus scrofa domestica). The results indicate presence of G proteins coupled P2Y receptors on ependymocytes and also P2X receptors engaged in fast signal transmission. Additionally we found in CSF nucleotides and adenosine in the concentration sufficient to P receptors activation. These extracellular nucleotides are metabolised by adenylate kinase and nucleotidases from at least two families: NTPDases and NPPases. A low activity of these nucleotide metabolising enzymes maintains nucleotides concentration in ventricular system in micromolar range. ATP is degraded into adenosine and inosine.

CONCLUSIONS

Our results confirm the thesis about cross-talking between brain and ventricular system functioning in physiological as well as pathological conditions. The close interaction of brain and ventricular system may elicit changes in qualitative and quantitative composition of purines and pyrimidines in CSF. These changes can be dependent on the physiological state of brain, including pathological processes in CNS.

Extracellular-purine metabolism in blood vessels (part I). Extracellular-purine level in blood of patients with abdominal aortic aneurysm

Adenosine and adenosine derivatives are the main regulators of purinoceptors (P1 and P2) mediated hemostasis and blood pressure. Since impaired hemostasis and high blood pressure lead to atherosclerosis and to the development of aneurysm, in this study we tested and compared the concentration of extracellular purines (e-purines) in the blood in of patients having abdominal aortic aneurysm with that from healthy volunteers. Whereas adenine nucleosides and nucleotides level in human blood plasma was analysed using reverse phase high performance liquid chromatography (HPLC), cholesterol concentration was estimated by an enzymatic assay. We did not find any correlation between e-purines concentration and the age of healthy volunteers. Furthermore, the sum level of e-purines (ATP, ADP, AMP, adenosine, and inosine) in the control group did not exceed 70 microM, while it was nearly two-fold higher in the blood of patients having abdominal aortic aneurysm, (123 microM). In a special case of people with Leriche Syndrome, a disease characterized by deep atherosclerotic changes, the e-purines level had further increased. Additionally, we also report typical atherosclerotic changes in the aorta using histological assays as well as total cholesterol rise. The significant rise in cholesterol concentration in the blood of the patients with abdominal aortas aneurysm, compared with the control groups, was not unique since 23% of the healthy people also exceeded the normal level of cholesterol. Therefore, our results strongly indicate that the estimation of e-purines concentration in the blood may serve as another indicator of atherosclerosis and warrant further consideration as a futuristic diagnostic tool.

Preservation of differentiation and clonogenic potential of human hematopoietic stem and progenitor cells during lyophilization and ambient storage

Progenitor cell therapies show great promise, but their potential for clinical applications requires improved storage and transportation. Desiccated cells stored at ambient temperature would provide economic and practical advantages over approaches employing cell freezing and subzero temperature storage. The objectives of this study were to assess a method for loading the stabilizing sugar, trehalose, into hematopoietic stem and progenitor cells (HPC) and to evaluate the effects of subsequent freeze-drying and storage at ambient temperature on differentiation and clonogenic potential. HPC were isolated from human umbilical cord blood and loaded with trehalose using an endogenous cell surface receptor, termed P2Z. Solution containing trehalose-loaded HPC was placed into vials, which were transferred to a tray freeze-dryer and removed during each step of the freeze-drying process to assess differentiation and clonogenic potential. Control groups for these experiments were freshly isolated HPC. Control cells formed 1450+/-230 CFU-GM, 430+/-140 BFU-E, and 50+/-40 CFU-GEMM per 50 microL. Compared to the values for the control cells, there was no statistical difference observed for cells removed at the end of the freezing step or at the end of primary drying. There was a gradual decrease in the number of CFU-GM and BFU-E for cells removed at different temperatures during secondary drying; however, there were no significant differences in the number of CFU-GEMM. To determine storage stability of lyophilized HPC, cells were stored for 4 weeks at 25 degrees C in the dark. Cells reconstituted immediately after lyophilization produced 580+/-90 CFU-GM ( approximately 40%, relative to unprocessed controls p<0.0001), 170+/-70 BFU-E (approximately 40%, p<0.0001), and 41+/-22 CFU-GEMM (approximately 82%, p = 0.4171), and cells reconstituted after 28 days at room temperature produced 513+/-170 CFU-GM (approximately 35%, relative to unprocessed controls, p<0.0001), 112+/-68 BFU-E (approximately 26%, p<0.0001), and 36+/-17 CFU-GEMM ( approximately 82%, p = 0.2164) These studies are the first to document high level retention of CFU-GEMM following lyophilization and storage for 4 weeks at 25 degrees C. This type of flexible storage stability would potentially permit the ability to ship and store HPC without the need for refrigeration.

Biochemical characterization of an ecto-ATP diphosphohydrolase activity in Candida parapsilosis and its possible role in adenosine acquisition and pathogenesis

In this work, we describe the ability of intact cells of Candida parapsilosis to hydrolyze extracellular ATP. ATP hydrolysis was stimulated by MgCl(2) in a dose-dependent manner. The ecto-ATPase activity was increased in the presence of 5 mM MgCl(2), with values of V(max) and apparent K(m) for Mg-ATP(2-) increasing to 33.80 +/- 1.2 nmol Pi h(-1) 10(-8) cells and 0.6 +/- 0.06 mM, respectively. Inhibitors of phosphatases, mitochondrial Mg(2+)-ATPases and Na(+)-ATPases had no effect on the C. parapsilosis Mg(2+)-stimulated ATPase activity, but extracellular impermeant compounds, 4,4'-diisothiocyanatostilbene-2,2'disulfonic acid and suramin, reduced enzyme activity in yeast living cells by 83.1% and 81.9%, respectively. ARL 67156 (6-N,N'-diethyl-d-beta-gamma-dibromomethylene ATP), a nucleotide analogue, also inhibited the ecto-ATPase activity in a dose-dependent manner. ATP was the best substrate for the yeast Mg(2+)-stimulated ecto-enzyme, but ADP, ITP, CTP, GTP and UTP were also hydrolyzed. A direct relationship between ecto-ATPase activity and adhesion to host cells was observed. In these assays, inhibition of enzyme activity resulted in decreased levels of yeast adhesion to epithelial cells. Based also on the differential expression of ecto-ATPase activities in the different isolates of C. parapsilosis, the possible role of this enzyme in fungal biology is discussed.

Recent patents on novel P2X(7) receptor antagonists and their potential for reducing central nervous system inflammation

Inflammation arises in the CNS from a number of neurodegenerative and oncogenic disorders, as well as from ischemic and traumatic brain injuries. These pathologies give rise to increased levels of extracellular adenine nucleotides which, via activation of a variety of cell surface P2 purinergic receptors, influence the inflammatory activities of responding immune cells. One P2 receptor subtype in particular, the P2X(7) receptor, potentiates the release of pro-inflammatory cytokines, such as interleukin-1beta (IL-1beta) from macrophage-like cells. It is also thought to contribute to secondary brain injury by inducing neuronal cell death. Therefore, antagonism of this receptor could have significant therapeutic impact on all disorders, not just CNS, to which excessive inflammatory activities contribute. The use of currently available P2X(7) receptor antagonists for the treatment of CNS inflammation has been limited to the generally non-selective antagonists PPADS, oxidized ATP, Brilliant Blue G, suramin, calmidizolium, and KN-62. However, the recent patents and development of novel P2X(7) receptor antagonists, as discussed in this review, will provide new tools both for clinical and research purposes. Here we discuss compounds for which patents have been applied since 2006, from the following categories: benzamide inhibitors, bicycloheteroaryl compounds, acylhdranzine antagonists, biaromatic P2X(7) antagonists, heterocyclic compounds and amide derivatives, and aromatic amine antagonists.

Extracellular NAD(+) induces a rise in [Ca(2+)](i) in activated human monocytes via engagement of P2Y(1) and P2Y(11) receptors

Extracellular nicotinamide adenine dinucleotide (NAD(+)) is known to increase the intracellular calcium concentration [Ca(2+)](i) in different cell types and by various mechanisms. Here we show that NAD(+) triggers a transient rise in [Ca(2+)](i) in human monocytes activated with lipopolysaccharide (LPS), which is caused by a release of Ca(2+) from IP(3)-responsive intracellular stores and an influx of extracellular Ca(2+). By the use of P2 receptor-selective agonists and antagonists we demonstrate that P2 receptors play a role in the NAD(+)-induced calcium response in activated monocytes. Of the two subclasses of P2 receptors (P2X and P2Y) the P2Y receptors were considered the most likely candidates, since they share calcium signaling properties with NAD(+). The identification of P2Y(1) and P2Y(11) as receptor subtypes responsible for the NAD(+)-triggered increase in [Ca(2+)](i) was supported by several lines of evidence. First, specific P2Y(1) and P2Y(11) receptor antagonists inhibited the NAD(+)-induced increase in [Ca(2+)](i). Second, NAD(+) was shown to potently induce calcium signals in cells transfected with either subtype, whereas untransfected cells were unresponsive. Third, NAD(+) caused an increase in [cAMP](i), prevented by the P2Y(11) receptor-specific antagonist NF157.

The purinergic receptor P2Y, G-protein coupled, 2 (P2RY2) gene associated with essential hypertension in Japanese men

P2RY2 has an important function in the regulation of blood pressure by activating adenosine triphosphate (ATP). The aim of this study was to investigate the association between the human P2RY2 gene and essential hypertension (EH) through a haplotype-based case-control study that included two gender groups. The 273 EH patients and 255 age-matched controls were genotyped for five single-nucleotide polymorphisms (SNPs) of the human P2RY2 gene (rs4944831, rs1783596, rs4944832, rs4382936 and rs10898909). Data were analysed for men and women separately and then as a combined total group. For the total and the men only groups, the genotype distribution of the T allele of rs4944831 and the recessive model (GG vs TG+TT) of rs4944831 differed significantly between the EH patients and controls (P=0.028 and 0.019; P=0.009 and 0.008, respectively). Logistic regression showed that for the total and men groups, the TG+TT genotype of rs4944831 was more prevalent in EH patients than in the controls (P=0.026 and 0.011, respectively). For men, the overall distribution of the haplotype (SNP2-SNP4-SNP5) was significantly different between the EH patients and the controls (P=0.006). As compared with controls, the frequency of the T-A-G haplotype was significantly higher, whereas the T-C-G haplotype was significantly lower for the EH patients (P=0.001 and 0.014, respectively). In conclusion, the present results indicate that rs4944831 and the T-A-G haplotype of the human P2RY2 gene might be genetic markers for EH in Japanese men.

Giardia lamblia: biochemical characterization of an ecto-ATPase activity

In this work, we describe the ability of living trophozoites of Giardia lamblia to hydrolyze extracellular ATP. In the absence of any divalent cations, a low level of ATP hydrolysis was observed (0.78+/-0.08 nmol Pi x h(-1)x10(-6) cells). The ATP hydrolysis was stimulated by MgCl(2) in a dose-dependent manner. Half maximum stimulation of ATP hydrolysis was obtained with 0.53+/-0.07 mM. ATP was the best substrate for this enzyme. The apparent K(m) for ATP was 0.21+/-0.04 mM. In the pH range from 5.6 to 8.4, in which cells were viable, this activity was not modified. The Mg(2+)-stimulated ATPase activity was insensitive to inhibitors of intracellular ATPases such as vanadate (P-ATPases), bafilomycin A(1) (V-ATPases), and oligomycin (F-ATPases). Inhibitors of acid phosphatases (molybdate, vanadate and fluoride) or alkaline phosphatases (levamizole) had no effect on the ecto-ATPase activity. The impermeant agent DIDS and suramin, an antagonist of P2 purinoreceptors and inhibitor of some ecto-ATPases, decreased the enzymatic activity in a dose-dependent manner, confirming the external localization of this enzyme. Besides ATP, trophozoites were also able to hydrolyse ADP and 5 AMP, but the hydrolysis of these nucleotides was not stimulated by MgCl(2). Our results are indicative of the occurrence of a G. lamblia ecto-ATPase activity that may have a role in parasite physiology.

Mechanical loading stimulates ecto-ATPase activity in human tendon cells

Response to external stimuli such as mechanical signals is critical for normal function of cells, especially when subjected to repetitive motion. Tenocytes receive mechanical stimuli from the load-bearing matrix as tension, compression, and shear stress during tendon gliding. Overloading a tendon by high strain, shear, or repetitive motion can cause matrix damage. Injury may induce cytokine expression, matrix metalloproteinase (MMP) expression and activation resulting in loss of biomechanical properties. These changes may result in tendinosis or tendinopathy. Alternatively, an immediate effector molecule may exist that acts in a signal-dampening pathway. Adenosine 5'-triphosphate (ATP) is a candidate signal blocker of mechanical stimuli. ATP suppresses load-inducible inflammatory genes in human tendon cells in vitro. ATP and other extracellular nucleotide signaling are regulated efficiently by two distinct mechanisms: purinoceptors via specific receptor-ligand binding and ecto-nucleotidases via the hydrolysis of specific nucleotide substrates. ATP is released from tendon cells by mechanical loading or by uridine 5'-triphosphate (UTP) stimulation. We hypothesized that mechanical loading might stimulate ecto-ATPase activity. Human tendon cells of surface epitenon (TSC) and internal compartment (TIF) were cyclically stretched (1 Hz, 0.035 strain, 2 h) with or without ATP. Aliquots of the supernatant fluids were collected at various time points, and ATP concentration (ATP) was determined by a luciferin-luciferase bioluminescence assay. Total RNA was isolated from TSC and TIF (three patients) and mRNA expression for ecto-nucleotidase was analyzed by RT-PCR. Human tendon cells secreted ATP in vitro (0.5-1 nM). Exogenous ATP was hydrolyzed within minutes. Mechanical load stimulated ATPase activity. ATP was hydrolyzed in mechanically loaded cultures at a significantly greater rate compared to no load controls. Tenocytes (TSC and TIF) expressed ecto-nucleotidase mRNA (ENTPD3 and ENPP1, ENPP2). These data suggest that motion may release ATP from tendon cells in vivo, where ecto-ATPase may also be activated to hydrolyze ATP quickly. Ecto-ATPase may act as a co-modulator in ATP load-signal modulation by regulating the half-life of extracellular purine nucleotides. The extracellular ATP/ATPase system may be important for tendon homeostasis by protecting tendon cells from responding to excessive load signals and activating injurious pathways.

P2 purinoceptors: historical perspective and classification

This article presents an overview that gives some historical perspective to the detailed papers at the cutting edge of P2 purinoceptor research that follow. I consider the proposal, first put forward by Abbracchio & Burnstock (Pharmacol Ther 64:445-475, 1994), that P2 purinoceptors should be regarded as members of two main families: a P2X purinoceptor family consisting of ligand-gated ion channels, and a P2Y purinoceptor family consisting of G protein-coupled receptors. The latest subclasses of these two families (P2X1-4 and P2Y1-5), identified largely on the basis of molecular cloning and expression, are tabled. Finally, I suggest some future directions for P2 purinoceptor research, including studies of the long-term (trophic) actions of purines, the evolution and development of purinoceptors and therapeutic applications.

Extracellular nucleotides regulate CCL20 release from human primary airway epithelial cells, monocytes and monocyte-derived dendritic cells

Extracellular nucleotides regulate ion transport and mucociliary clearance in human airway epithelial cells (HAECs) via the activation of P2 receptors, especially P2Y(2). Therefore, P2Y(2) receptor agonists represent potential pharmacotherapeutic agents to treat cystic fibrosis (CF). Nucleotides also modulate inflammatory properties of immune cells like dendritic cells (DCs), which play an important role in mucosal immunity. Using DNA-microarray experiments, quantitative RT-PCR and cytokine measurements, we show here that UTP up-regulated approximately 2- to 3-fold the antimicrobial chemokine CCL20 expression and release in primary HAECs cultured on permeable supports at an air-liquid interface (ALI). Both P2Y(2) (ATPgammaS, UTP, INS365) and P2Y(6) (UDP, INS48823) agonists increased CCL20 release. UTP-induced CCL20 release was insensitive to NF-kappaB pathway inhibitors but sensitive to inhibitors of ERK1/2 and p38/MAPK pathways. Furthermore, UTP had no effect on interleukin-(IL)-8 release and reduced the release of both CCL20 and IL-8 induced by TNF-alpha and LPS. Accordingly, UTP reduced the capacity of basolateral supernatants of HAECs treated with TNF-alpha or LPS to induce the chemoattraction of both CD4(+) T lymphocytes and neutrophils. In addition, we show that, in monocyte-derived DCs, ATPgammaS, and UDP but not UTP/INS365-stimulated CCL20 release. Likewise, UDP but not ATPgammaS was also able to increase CCL20 release from monocytes. Pharmacological experiments suggested an involvement of P2Y(11) or P2Y(6) receptors through NF-kappaB, ERK1/2, and p38/MAPK pathways. Altogether, our data demonstrate that nucleotides may modulate chemokine release and leukocyte recruitment in inflamed airways by acting on both epithelial and immune cells. Our results could be relevant for further clinical investigations in CF.

The action of extracellular NAD+ on gluconeogenesis in the perfused rat liver

In the rat liver NAD+ infusion produces increases in portal perfusion pressure and glycogenolysis and transient inhibition of oxygen consumption. The aim of the present work was to investigate the possible action of this agent on gluconeogenesis using lactate as a gluconeogenic precursor. Hemoglobin-free rat liver perfusion in antegrade and retrograde modes was used with enzymatic determination of glucose production and polarographic assay of oxygen uptake. NAD+ infusion into the portal vein (antegrade perfusion) produced a concentration-dependent (25-100 microM) transient inhibition of oxygen uptake and gluconeogenesis. For both parameters inhibition was followed by stimulation. NAD+ infusion into the hepatic vein (retrograde perfusion) produced only transient stimulations. During Ca2+-free perfusion the action of NAD+ was restricted to small transient stimulations. Inhibitors of eicosanoid synthesis with different specificities (indo-methacin, nordihydroguaiaretic acid, bromophenacyl bromide) either inhibited or changed the action of NAD+. The action of NAD+ on gluconeogenesis is probably mediated by eicosanoids synthesized in non-parenchymal cells. As in the fed state, in the fasted condition extracellular NAD+ is also able to exert two opposite effects, inhibition and stimulation. Since inhibition did not manifest significantly in retrograde perfusion it is likely that the generating signal is located in pre-sinusoidal regions.

Trypanosoma rangeli: characterization of a Mg-dependent ecto ATP-diphosphohydrolase activity

In this work we describe the ability of living Trypanosoma rangeli to hydrolyze extracellular ATP. In these intact parasites whose viability was assessed before and after the reactions by motility and by Trypan blue dye exclusion, there was a low level of ATP hydrolysis in the absence of any divalent metal (1.53+/-0.12 nmol P(i)/h x 10(7) cells). The ATP hydrolysis was stimulated by MgCl(2) and the Mg-dependent ecto-ATPase activity was 5.24+/-0.64 nmol P(i)/h x 10(7) cells. The Mg-dependent ecto-ATPase activity was linear with cell density and with time for at least 60 min. This stimulatory effect on the ATP hydrolysis was also observed when MgCl(2) was replaced by MnCl(2), but not by CaCl(2), SrCl(2), and ZnCl(2). The apparent K(m) for Mg-ATP2- was 0.53+/-0.11 mM. The optimum pH for the T. rangeli Mg-dependent ecto-ATPase activity lies in the alkaline range. This ecto-ATPase activity was insensitive to inhibitors of other ATPase and phosphatase activities, such as oligomycin, sodium azide, bafilomycin A1, ouabain, furosemide, vanadate, molybdate, sodium fluoride, tartrate, and levamizole. To confirm that this Mg-dependent ATPase was an ecto-ATPase, we used an impermeant inhibitor, DIDS (4, 4'-diisothiocyanostylbene 2'-2'-disulfonic acid) as well as suramin, an antagonist of P2 purinoreceptors and inhibitor of some ecto-ATPases. These two reagents inhibited the Mg(2+)-dependent ATPase activity in a dose-dependent manner. This ecto-ATPase activity was stimulated by carbohydrates involved in the attachment/invasion of salivary glands of Rhodnius prolixus and by lipophorin, an insect lipoprotein circulating in the hemolymph.

Application of solid phase extraction and high-performance liquid chromatography to qualitative and quantitative analysis of nucleotides and nucleosides in human cerebrospinal fluid

New method of qualitative and quantitative analysis of nucleotides in human cerebrospinal fluid (CSF), based on the combination of extraction of purines and pyrimidines to the solid phase (SPE) and high-performance liquid chromatography (HPLC), was proposed. Use of SPE and lyophilization of samples allowed for the first time to detect the presence of di- and triphosphonucleotides in human CSF. Concentration of those compounds varied from 0.003 to 5.0 microM. Differences in the nucleotide mixture composition in human CSF detected with the new method are coupled with the neurological disorders and might be a basis for an efficient diagnostic tool.

Role of interstitial ATP and adenosine in the regulation of renal hemodynamics and microvascular function

The role of adenosine in the regulation of renal hemodynamics and function has been studied extensively; however, another purine agent, ATP, is also gaining recognition for its paracrine role in the kidney. Adenosine and ATP bind to specific membrane-bound P1 and P2 purinoceptors, respectively, and initiate a variety of biological effects on renal microvascular tone, mesangial cell function, and renal epithelial transport. The purpose of this review is to summarize the potential roles of interstitial ATP and adenosine as regulators of renal hemodynamics and microcirculation. In vitro blood-perfused juxtamedullary nephron preparation was used to assess the roles of ATP and adenosine in the regulation of renal microvascular tone. This approach mimics the adventitial exposure of renal microvascular smooth muscle to ATP and adenosine synthesized locally and released into the interstitial fluid. ATP selectively vasoconstricts afferent but not efferent arterioles via P2X and P2Y receptors, whereas, adenosine vasoconstricts both vascular segments via activation of adenosine A(1) receptors. Furthermore, selective P2X and P2Y receptor stimulation increases intracellular calcium concentration in vascular smooth muscle cells that are freshly isolated from the preglomerular microvasculature. These data support the hypothesis that interstitial ATP plays a critical role in the control of renal microvascular function through mechanisms that are independent of adenosine receptors. We have recently developed a renal microdialysis method to determine the dynamics of ATP and adenosine levels in the renal cortical interstitium. In this review, we also summarize current knowledge pertaining to the alterations in renal interstitial ATP and adenosine in some pathophysiological conditions.

Adenosine triphosphate induces activation of caspase-3 in apoptosis of human granulosa-luteal cells

Adenosine triphosphate (ATP) has been shown to induce programmed cell death in various systems. However, little is known about the effect of ATP on human granulosa-luteal cells (hGLCs). The present study was designed to examine the effect of ATP on the activation of the caspase signaling pathway and its role in inducing programmed cell death. Human GLCs were collected from patients undergoing in vitro fertilization programs, and then were cultured in FBS-supplemented DMEM for 3 days prior to our studies. To examine the dose-response relationship, hGLCs were treated with increasing concentrations of ATP (10 microM, 100 microM, 1 mM or 10 mM) for 24 hours. For time-course experiments, hGLCs were treated with 10 mM ATP for 6, 12, or 24 hours. Western blot analysis was performed using antibodies against the pro- and active forms of caspase-3, -9, or PARP. To quantify the induction of apoptosis, DNA fragmentation was measured using the cell death detection enzyme-linked immunosorbent assay. To examine the effect of human chorionic gonadotropin (hCG) in protecting cells from apoptosis, hGLCs were treated with 10 IU hCG in the presence of 10 mM ATP for 12 hours. It was demonstrated that ATP was capable of inducing DNA fragmentation in a dose- and time-dependent manner. Furthermore, Western blot analysis, which detected the pro- and active forms of caspase-3, or PARP, demonstrated that ATP activated the caspase-signaling pathway, leading to the proteolytic conversion of pro-caspase-3 to active caspase-3, and the subsequent cleavage of the caspase substrate PARP. Based on our observation, caspase-9 was not triggered by ATP. Interestingly, hCG attenuated the effect of ATP in activating the caspase signaling pathway. To our knowledge, this is the first demonstration of the ATP-induced activation of the caspase signaling pathway in the human ovary. These results support the notion that the caspase-signaling pathway is involved in mediating ATP actions in the human ovary.

Potential value of adenosine 5'-triphosphate (ATP) and adenosine in anaesthesia and intensive care medicine

Extracellular adenosine and adenosine triphosphate (ATP) are involved in biological processes including neurotransmission, muscle contraction, cardiac function, platelet function, vasodilatation, signal transduction and secretion in a variety of cell types. They are released from the cytoplasm of several cell types and interact with specific purinergic receptors which are present on the surface of many cells. This review summarizes the evidence on the potential value and applicability of ATP (not restricted to ATP-MgCl(2)) and adenosine in the field of anaesthesia and intensive care medicine. It focuses, in particular, on evidence and roles in treatment of acute and chronic pain and in sepsis. Based on the evidence from animal and clinical studies performed during the last 20 years, ATP could provide a valuable addition to the therapeutic options in anaesthesia and intensive care medicine. It may have particular roles in pain management, modulation of haemodynamics and treatment of shock.

P2X receptor-stimulated calcium responses in preglomerular vascular smooth muscle cells involves 20-hydroxyeicosatetraenoic acid

The current study tested the hypothesis that endogenous 20-hydroxyeicosatetraenoic acid (20-HETE) contributes to the increase in intracellular calcium ([Ca2+]i) elicited by P2X receptor activation in renal microvascular smooth muscle cells. Vascular smooth muscle cells obtained from rats were loaded with fura-2 and studied using standard single cell fluorescence microscopy. Basal renal myocyte [Ca2+]i averaged 96 +/- 5 nM. ATP (10 and 100 microM) increased vascular smooth muscle cell [Ca2+]i by 340 +/- 88 and 555 +/- 80 nM, respectively. The cytochrome P450 hydroxylase inhibitor, N-methylsulfonyl-12,12-dibromododec-11-enamide (DDMS), or the 20-HETE antagonist, 20-hydroxyeicosa-6(Z),15(Z)-dienoic acid (20-HEDE), significantly attenuated the peak myocyte [Ca2+]i responses to 10 and 100 microM ATP. ATP (100 microM) increased vascular smooth muscle cell [Ca2+]i by 372 +/- 93 and 163 +/- 55 nM in the presence of DDMS or 20-HEDE, respectively. The P2X receptor agonist, alpha,beta-methylene-ATP (10 microM), increased myocyte [Ca2+]i by 78 +/- 12 nM, and this response was significantly attenuated by DDMS (40 +/- 15 nM). In contrast, the vascular smooth muscle cell [Ca2+]i evoked by the P2Y agonist, UTP (100 microM), was not altered by DDMS or 20-HEDE. The effect of 20-HETE on [Ca2+]i was also assessed, and the peak increases in [Ca2+]i averaged 62 +/- 12 and 146 +/- 70 nM at 20-HETE concentrations of 1 and 10 microM, respectively. These results demonstrate that 20-HETE plays a significant role in the renal microvascular smooth muscle cell [Ca2+]i response to P2X receptor activation.

A Mg-dependent ecto-ATPase is increased in the infective stages of Trypanosoma cruzi

In this work, we describe the ability of living epimastigotes of Trypanosoma cruzi to hydrolyze extracellular ATP. In these intact parasites, there was a low level of ATP hydrolysis in the absence of any divalent metal (2.42 +/- 0.31 nmol Pi/h x 10(8) cells). ATP hydrolysis was stimulated by MgCl2, and the Mg-dependent ecto-ATPase activity was 27.15 +/- 2.91 nmol Pi/h x 10(8) cells. The addition of MgCl2 to the extracellular medium increased the ecto-ATPase activity in a dose-dependent manner. This stimulatory activity was also observed when MgCl2 was replaced by MnCl2, but not by CaCl2 or SrCl2. The apparent Km for Mg-ATP2- was 0.61 mM, and free Mg2+ did not increase the ecto-ATPase activity. This ecto-ATPase activity was insensitive to the inhibitors of other ATPase and phosphatase activities. To confirm that this Mg-dependent ATPase was an ecto-ATPase, we used an impermeant inhibitor, DIDS (4, 4'.diisothiocyanostylbene 2'-2'-disulfonic acid) as well as suramin, an antagonist of P2 purinoreceptors and inhibitor of some ecto-ATPases. These two reagents inhibited the Mg2+-dependent ATPase activity in a dose-dependent manner. A comparison among the Mg2+-ecto-ATPase activities of the three forms of T. cruzi showed that the noninfective epimastigotes were less efficient at hydrolyzing ATP than the infective trypomastigote and amastigote stages.

The hemodynamic effects of ATP in retrograde perfusion of the bivascularly perfused rat liver

AIMS/BACKGROUND

In the sinusoidal bed the distribution of water is flow-limited, but it becomes partly barrier-limited when adenosine triphosphate (ATP) is introduced. This effect could be exerted either directly by ATP or by substances released from presinusoidal regions. Furthermore, portally infused ATP seems to be able to diffuse in the direction of the arterial bed. It is not known if this diffusion route is specific. Answers to these questions can be obtained from indicator-dilution experiments in retrograde perfusion.

METHODS

Indicator-dilution experiments, using [14C]sucrose and [3H]water, were conducted. Rat livers were perfused in the retrograde mode (hepatic vein+hepatic artery --> portal vein).

RESULTS

When ATP was infused into the hepatic vein, the distribution of [3H]water remained essentially flow-limited. The infusion of ATP into the hepatic artery increased the sucrose and extra-sucrose spaces of the arterial bed, but infusion into the hepatic vein was without effect.

CONCLUSIONS

The results indicate that the induction of barrier-limited distribution of [3H]water is not a direct effect of ATP. Furthermore, if the transhepatic diffusion of ATP can occur from presinusoidal regions to the arterial bed, as shown by previous work, a similar diffusion does not occur from postsinusoidal regions.

An ecto-protein tyrosine phosphatase of Entamoeba histolytica induces cellular detachment by disruption of actin filaments in HeLa cells

Actin cytoskeleton disruption in host cells has been demonstrated for PTPases from pathogenic microorganisms. In this work, we analysed whether the secreted acid phosphatase from Entamoeba histolytica has phosphotyrosine phosphatase activity and the possibility that this activity may participate in damaging host cells. The secreted acid phosphatase of E. histolytica, which catalyses p-nitrophenyl phosphate hydrolysis at acid pH values, was found to have phosphotyrosine phosphatase activity. The enzymatic properties of phosphotyrosine phosphatase and acid phosphatase were virtually identical and included: Km values of 10 x 10(-4) M, no requirement for divalent cations, and sensitivity to molybdate, vanadate, and tungstate. The phosphotyrosyl phosphatase activity caused significant levels of cell rounding and detachment correlating with disruption of the actin stress fibres in HeLa cells. Thus, our data suggest that secreted phosphotyrosine phosphatase could play a cytotoxic role during amoebic infection.

ATP modulates load-inducible IL-1beta, COX 2, and MMP-3 gene expression in human tendon cells

Tendon cells receive mechanical signals from the load bearing matrices. The response to mechanical stimulation is crucial for tendon function. However, overloading tendon cells may deteriorate extracellular matrix integrity by activating intrinsic factors such as matrix metalloproteinases (MMPs) that trigger matrix destruction. We hypothesized that mechanical loading might induce interleukin-1beta (IL-1beta) in tendon cells, which can induce MMPs, and that extracellular ATP might inhibit the load-inducible gene expression. Human tendon cells isolated from flexor digitorum profundus tendons (FDPs) of four patients were made quiescent and treated with ATP (10 or 100 microM) for 5 min, then stretched equibiaxially (1 Hz, 3.5% elongation) for 2 h followed by an 18-h-rest period. Stretching induced IL-1beta, cyclooxygenase 2 (COX 2), and MMP-3 genes but not MMP-1. ATP reduced the load-inducible gene expression but had no effect alone. A medium change caused tendon cells to secrete ATP into the medium, as did exogenous UTP. The data demonstrate that mechanical loading induces ATP release in tendon cells and stimulates expression of IL-1beta, COX 2, and MMP-3. Load-induced endogenous IL-1beta may trigger matrix remodeling or a more destructive pathway(s) involving IL-1beta, COX 2, and MMP-3. Concomitant autocrine and paracrine release of ATP may serve as a negative feedback mechanism to limit activation of such an injurious pathway. Attenuation or failure of this negative feedback mechanism may result in the progression to tendinosis.

Characterization of the NTPDase activities in the mesentery pre- and post-capillary circuits of the guinea pig

NTPDase is one of the principal enzymes involved in the sequential hydrolysis of ATP. In the present study, the presence and functionality of NTPDase in the mesenteric vein and artery were examined. Adenosine triphosphate (ATP) (0.01-1000 pmol) induces a dose-dependent vasodilation in the isolated arterial and venous mesenteric vasculatures of the guinea pig. Adenosine diphosphate (ADP) (0.01-1000 pmol) but not adenosine monophosphate (AMP) (0.01-1000 pmol) induces a similar response in the mesenteric vascular circuit. L-NAME, a nitric oxide synthase inhibitor (200 microM, 30 min), significantly reduces the arterial dilatory effect of ATP and abolishes the responses to ADP and AMP. Complete removal of the endothelium with 3-[(3-cholamidopropyl) dimethylammonio]-1-propansulfonate (CHAPS) (20 mM, 2 x 45 s) abolishes ATP-induced responses. Infusion of ATP in the vascular circuit generated detectable amounts of ADP and AMP, as measured by HPLC. CHAPS treatment significantly reduced the level of ATP and the production of AMP in the arterial mesenteric circuit. In contrast to the arterial mesenteric vasculature, endothelium removal in the venous circuit triggered a marked potentiation of ADP release and, interestingly, a marked reduction in the release of AMP. Moreover, a specific inhibitor of NTP diphosphohydrolase, 1-hydroxynaphthlene-3,6-disulfonic acid BGO 136 (10 mM for 20 min), significatively reduced AMP production in both vascular preparations. These results confirm that the endothelium contributes to the vasoactive properties of ATP, ADP, and AMP. Our data also demonstrated a significant role of endothelium in NTPDase activity on ADP and AMP production prior to exogenous administration of ATP. The activity of this particular enzyme appears to be different from the reaction products viewpoint (i.e., the production of ADP) in the pre- and post-mesenteric circuits, suggesting two different isoforms with different substrate specificities.

Adenosine triphosphate activates mitogen-activated protein kinase in pre-neoplastic and neoplastic ovarian surface epithelial cells

To investigate the role of ATP in ovarian tumorigenesis, the present study examined the expression of the P2U purinoceptor (P2U-R) and effect of ATP on growth stimulation in pre-neoplastic and neoplastic ovarian surface epithelial (OSE) cells. The immortalized OSE (IOSE) cell lines, including IOSE-29 (pre-neoplastic), IOSE-29EC (neoplastic), and OVCAR-3 (ovarian adenocarcinoma cell line) were used. Our results indicated that P2U-R mRNA was expressed and that ATP exerted a growth-stimulatory effect in IOSE-29, IOSE-29EC, and OVCAR-3. To investigate the mechanism of the growth-stimulatory effect, the activation of mitogen-activated protein kinases (MAPKs) by ATP was examined. Treatment with ATP resulted in MAPK activation in IOSE-29 and IOSE-29EC cells, whereas the stimulatory effect of ATP in cellular proliferation and MAPK activation was completely abolished in the presence of PD98059 (an MAPK/ERK kinase inhibitor) and staurosporin (a protein kinase C inhibitor), suggesting that the growth stimulatory effect of ATP is mediated via protein kinase C-dependent MAPK activation in pre-neoplastic and neoplastic OSE cells. In a time-dependent study, ATP significantly increased MAPK activity at 5-20 min in IOSE-29 cells. Activated MAPK declined to control levels after 20 min in these cells. Treatment with ATP significantly induced MAPK activation after 5 min and was sustained for 60 min in IOSE-29EC cells. In addition, treatment with ATP resulted in substantial phosphorylation of Elk-1, the Ets family transcriptional factor, confirming that ATP action is mediated by activation of MAPK. In conclusion, we have demonstrated that P2U-R was expressed and that ATP induced growth stimulation in IOSE and OVCAR-3 cells. Furthermore, treatment with ATP resulted in the activation of an MAPK cascade and phosphorylation of Elk-1 in IOSE-29 and IOSE-29EC cells. These results suggest that the MAPK cascade may be involved in growth stimulation in response to ATP in pre-neoplastic and neoplastic OSE cells.

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.

Adenosine inhibition via A(1) receptor of N-type Ca(2+) current and peptide release from isolated neurohypophysial terminals of the rat

Effects of adenosine on voltage-gated Ca(2+) channel currents and on arginine vasopressin (AVP) and oxytocin (OT) release from isolated neurohypophysial (NH) terminals of the rat were investigated using perforated-patch clamp recordings and hormone-specific radioimmunoassays. Adenosine, but not adenosine 5'-triphosphate (ATP), dose-dependently and reversibly inhibited the transient component of the whole-terminal Ba(2+) currents, with an IC(50) of 0.875 microM. Adenosine strongly inhibited, in a dose-dependent manner (IC(50) = 2.67 microM), depolarization-triggered AVP and OT release from isolated NH terminals. Adenosine and the N-type Ca(2+) channel blocker omega-conotoxin GVIA, but not other Ca(2+) channel-type antagonists, inhibited the same transient component of the Ba(2+) current. Other components such as the L-, Q- and R-type channels, however, were insensitive to adenosine. Similarly, only adenosine and omega-conotoxin GVIA were able to inhibit the same component of AVP release. A(1) receptor agonists, but not other purinoceptor-type agonists, inhibited the same transient component of the Ba(2+) current as adenosine. Furthermore, the A(1) receptor antagonist 8-cyclopentyltheophylline (CPT), but not the A(2) receptor antagonist 3, 7-dimethyl-1-propargylxanthine (DMPGX), reversed inhibition of this current component by adenosine. The inhibition of AVP and OT release also appeared to be via the A(1) receptor, since it was reversed by CPT. We therefore conclude that adenosine, acting via A(1) receptors, specifically blocks the terminal N-type Ca(2+) channel thus leading to inhibition of the release of both AVP and OT.

Changes in distribution spaces and cell permeability caused by ATP in the rat liver

AIMS/BACKGROUND

Cellular and extracellular volume changes caused by ATP were investigated in the liver as well as the possible formation of diffusion barriers, which could be responsible for some of its metabolic effects.

METHODS

The experimental system was the bivascularly perfused rat liver. [(14)C]Sucrose and [(3)H]water were simultaneously injected into either the portal vein or the hepatic artery. Mean transit times, distribution spaces, variances and linear superimpositions were calculated.

RESULTS

In the portal system, ATP reduced the transit time in the great vessels, had little or no effect on sinusoidal and cellular spaces, but impaired the flow-limited distribution of both [(14)C]sucrose and [(3)H]water. In the arterial bed ATP infused into either the portal vein or the hepatic artery produced vasodilation and increased the aqueous extra-sucrose space. These effects were inhibited by Nomega-nitro-L-arginine methyl ester infused into the hepatic artery.

CONCLUSIONS

Sucrose and extra-sucrose space changes caused in the arterial bed by portally infused ATP are most probably analogous to the transhepatic vasodilation effect already described for the rabbit liver. Impairment of flow-limited distribution of tracers in the sinusoidal bed indicates that ATP induces the formation of permeability barriers, which could be responsible for some of its metabolic effects.

P2 receptor-mediated afferent arteriolar vasoconstriction during calcium blockade

Experiments were performed to determine the role of L-type calcium channels on the afferent arteriolar vasoconstrictor response to ATP and UTP. With the use of the blood-perfused juxtamedullary nephron technique, kidneys were perfused at 110 mmHg and the responses of arterioles to alpha,beta-methylene ATP, ATP, and UTP were determined before and during calcium channel blockade with diltiazem. alpha,beta-Methylene ATP (1.0 microM) decreased arteriolar diameter by 8 +/- 1% under control conditions. This response was abolished during calcium channel blockade. In contrast, 10 microM UTP reduced afferent arteriolar diameter to a similar degree before (20 +/- 4%) and during (14 +/- 4%) diltiazem treatment. Additionally, diltiazem completely prevented the vasoconstriction normally observed with ATP concentrations below 10 microM and attenuated the response obtained with 10 microM ATP. These data demonstrate that L-type calcium channels play a significant role in the vasoconstrictor influences of alpha,beta-methylene ATP and ATP but not UTP. The data also suggest that other calcium influx pathways may participate in the vasoconstrictor response evoked by P2 receptor activation. These observations support previous findings that UTP-mediated elevation of intracellular calcium concentration in preglomerular vascular smooth muscle cells relies primarily on calcium release from intracellular pools, whereas ATP-mediated responses involve both voltage-dependent calcium influx, through L-type calcium channels, and the release of calcium from intracellular stores. These results support the argument that P2X and P2Y receptors influence the diameter of afferent arterioles through activation of disparate signal transduction mechanisms.

Ectonucleotidase activities in Sertoli cells from immature rats

Sertoli cells have been shown to be targets for extracellular purines such as ATP and adenosine. These purines evoke responses in Sertoli cells through two subtypes of purinoreceptors, P2Y2 and P A1. The signals to purinoreceptors are usually terminated by the action of ectonucleotidases. To demonstrate these enzymatic activities, we cultured rat Sertoli cells for four days and then used them for different assays. ATP, ADP and AMP hydrolysis was estimated by measuring the Pi released using a colorimetric method. Adenosine deaminase activity (EC 3.5.4.4) was determined by HPLC. The cells were not disrupted after 40 min of incubation and the enzymatic activities were considered to be ectocellularly localized. ATP and ADP hydrolysis was markedly increased by the addition of divalent cations to the reaction medium. A competition plot demonstrated that only one enzymatic site is responsible for the hydrolysis of ATP and ADP. This result indicates that the enzyme that acts on the degradation of tri- and diphosphate nucleosides on the surface of Sertoli cells is a true ATP diphosphohydrolase (EC 3.6.1.5) (specific activities of 113 +/- 6 and 21 +/- 2 nmol Pi mg(-1) min(-1) for ATP and ADP, respectively). The ecto-5'-nucleotidase (EC 3.1.3.5) and ectoadenosine deaminase activities (specific activities of 32 +/- 2 nmol Pi mg(-1) min(-1) for AMP and 1.52 +/- 0.13 nmol adenosine mg(-1) min(-1), respectively) were shown to be able to terminate the effects of purines and may be relevant for the physiological control of extracellular levels of nucleotides and nucleosides inside the seminiferous tubules.

Agonists of the P2Y(AC)-receptor activate MAP kinase by a ras-independent pathway in rat C6 glioma

We have previously shown that an ecto-NPPase modulates the ATP- and ADP-mediated P2Y(AC)-receptor activation in rat C6 glioma. In the present study, 2MeSADP and Ap(3)A induced no detectable PI turnover and were identified as specific agonists of the P2Y(AC)-receptor with EC(50) values of 250 +/- 37 pM and 1 +/- 0.5 microM, respectively. P2Y(AC)-receptor stimulation increased MAP kinase (ERK1/2) activation that returned to the basal level 4 h after stimulation and was correlated with a gradual desensitization of the P2Y(AC)-purinoceptor. The purinoceptor antagonists DIDS and RB2 blocked MAP kinase activation. An IP(3)-independent Ca(2+)-influx was observed after P2Y(AC)-receptor activation. Inhibition of this influx by Ca(2+)-chelation, did not affect MAP kinase activation. Pertussis toxin, toxin B, selective PKC-inhibitors and a specific MEK-inhibitor inhibited the 2MeSADP- and Ap(3)A-induced MAP kinase activation. In addition, transfection with dominant negative RhoA(Asn19) rendered C6 cells insensitive to P2Y(AC)-receptor-mediated MAP kinase activation whereas dominant negative ras was without effect. Immunoprecipitation experiments indicated a significant increase in the phosphorylation of raf-1 after P2Y(AC)-receptor activation. We may conclude that P2Y(AC)-purinoceptor agonists activate MAP kinase through a G(i)-RhoA-PKC-raf-MEK-dependent, but ras- and Ca(2+)-independent cascade.

A Mg-dependent ecto-ATPase in Leishmania amazonensis and its possible role in adenosine acquisition and virulence

The plasma membrane of cells contains enzymes whose active sites face the external medium rather than the cytoplasm. The activities of these enzymes, referred to as ectoenzymes, can be measured using living cells. In this work we describe the ability of living promastigotes of Leishmania amazonensis to hydrolyze extracellular ATP. In these intact parasites whose viability was assessed before and after the reactions by motility and by trypan blue dye exclusion, there was a low level of ATP hydrolysis in the absence of any divalent metal (5.39 +/- 0.71 nmol P(i)/h x 10(7) cells). The ATP hydrolysis was stimulated by MgCl(2) and the Mg-dependent ecto-ATPase activity was 30.75 +/- 2.64 nmol P(i)/h x 10(7) cells. The Mg-dependent ecto-ATPase activity was linear with cell density and with time for at least 60 min. The addition of MgCl(2) to extracellular medium increased the ecto-ATPase activity in a dose-dependent manner. At 5 mM ATP, half-maximal stimulation of ATP hydrolysis was obtained with 1.21 mM MgCl(2). This stimulatory activity was also observed when MgCl(2) was replaced by MnCl(2), but not by CaCl(2) or SrCl(2). The apparent K(m) for Mg-ATP(2-) was 0.98 mM and free Mg(2+) did not increase the ecto-ATPase activity. In the pH range from 6.8 to 8.4, in which the cells were viable, the acid phosphatase activity decreased, while the Mg(2+)-dependent ATPase activity increased. This ecto-ATPase activity was insensitive to inhibitors of other ATPase and phosphatase activities, such as oligomycin, sodium azide, bafilomycin A(1), ouabain, furosemide, vanadate, molybdate, sodium fluoride, tartrate, and levamizole. To confirm that this Mg-dependent ATPase was an ecto-ATPase, we used an impermeant inhibitor, 4,4'-diisothiocyanostylbene 2',2'-disulfonic acid as well as suramin, an antagonist of P(2) purinoreceptors and inhibitor of some ecto-ATPases. These two reagents inhibited the Mg(2+)-dependent ATPase activity in a dose-dependent manner. A comparison between the Mg(2+)-dependent ATPase activity of virulent and avirulent promastigotes showed that avirulent promastigotes were less efficient than the virulent promastigotes in hydrolyzing ATP.

Calcium signaling pathways utilized by P2X receptors in freshly isolated preglomerular MVSMC

This study tested the hypothesis that P2X receptor activation increases intracellular Ca(2+) concentration ([Ca(2+)](i)) in preglomerular microvascular smooth muscle cells (MVSMC) by evoking voltage-dependent calcium influx. MVSMC were obtained and loaded with the calcium-sensitive dye fura 2 and studied by using single-cell fluorescence microscopy. The effect of P2X receptor activation on [Ca(2+)](i) was assessed by using the P2X receptor-selective agonist alpha,beta-methylene-ATP and was compared with responses elicited by the endogenous P2 receptor agonist ATP. alpha,beta-Methylene-ATP increased [Ca(2+)](i) dose dependently. Peak increases in [Ca(2+)](i) averaged 37 +/- 11, 73 +/- 15, and 103 +/- 21 nM at agonist concentrations of 0.1, 1, and 10 microM, respectively. The average peak response elicited by 10 microM alpha,beta-methylene-ATP was approximately 34% of the response obtained with 10 microM ATP. alpha,beta-Methylene-ATP induced a transient increase in [Ca(2+)](i) before [Ca(2+)](i) returned to baseline, whereas ATP induced a biphasic response including a peak response followed by a sustained plateau. In Ca(2+)-free medium, ATP induced a sharp transient increase in [Ca(2+)](i), whereas the response to alpha,beta-methylene-ATP was abolished. Ca(2+) channel blockade with 10 microM diltiazem or nifedipine attenuated the response to alpha,beta-methylene-ATP, whereas nonspecific blockade of Ca(2+) influx pathways with 5 mM Ni(2+) abolished the response. Blockade of P2X receptors with the novel P2X receptor antagonist NF-279 completely but reversibly abolished the response to alpha,beta-methylene-ATP. These results indicate that P2X receptor activation by alpha,beta-methylene-ATP increases [Ca(2+)](i) in preglomerular MVSMC, in part, by stimulating voltage-dependent Ca(2+) influx through L-type Ca(2+) channels.

P2 receptors in regulation of renal microvascular function

In the last 10-15 years, interest in the physiological role of P2 receptors has grown rapidly. Cellular, tissue, and organ responses to P2 receptor activation have been described in numerous in vivo and in vitro models. The purpose of this review is to provide an update of the recent advances made in determining the involvement of P2 receptors in the control of renal hemodynamics and the renal microcirculation. Special attention will be paid to work published in the last 5-6 years directed at understanding the role of P2 receptors in the physiological control of renal microvascular function. Several investigators have begun to evaluate the effects of P2 receptor activation on renal microvascular function across several species. In vivo and in vitro evidence consistently supports the hypothesis that P2 receptor activation by locally released extracellular nucleotides influences microvascular function. Extracellular nucleotides selectively influence preglomerular resistance without having an effect on postglomerular tone. P2 receptor inactivation blocks autoregulatory behavior whereas responsiveness to other vasoconstrictor agonists is retained. P2 receptor stimulation activates multiple intracellular signal transduction pathways in preglomerular smooth muscle cells and mesangial cells. Renal microvascular cells and mesangial cells express multiple subtypes of P2 receptors; however, the specific role each plays in regulating vascular and mesangial cell function remains unclear. Accordingly, the results of studies performed to date provide strong support for the hypothesis that P2 receptors are important contributors to the physiological regulation of renal microvascular and/or glomerular function.

Adenosine 5'-triphosphate: a P2-purinergic agonist in the myocardium

ATP, besides an intracellular energy source, is an agonist when applied to a variety of different cells including cardiomyocytes. Sources of ATP in the extracellular milieu are multiple. Extracellular ATP is rapidly degraded by ectonucleotidases. Today ionotropic P2X(1--7) receptors and metabotropic P2Y(1,2,4,6,11) receptors have been cloned and their mRNA found in cardiomyocytes. On a single cardiomyocyte, micromolar ATP induces nonspecific cationic and Cl(-) currents that depolarize the cells. ATP both increases directly via a G(s) protein and decreases Ca(2+) current. ATP activates the inward-rectifying currents (ACh- and ATP-activated K(+) currents) and outward K(+) currents. P2-purinergic stimulation increases cAMP by activating adenylyl cyclase isoform V. It also involves tyrosine kinases to activate phospholipase C-gamma to produce inositol 1,4,5-trisphosphate and Cl(-)/HCO(3)(-) exchange to induce a large transient acidosis. No clear correlation is presently possible between an effect and the activation of a given P2-receptor subtype in cardiomyocytes. ATP itself is generally a positive inotropic agent. Upon rapid application to cells, ATP induces various forms of arrhythmia. At the tissue level, arrhythmia could be due to slowing of electrical spread after both Na(+) current decrease and cell-to-cell uncoupling as well as cell depolarization and Ca(2+) current increase. In as much as the information is available, this review also reports analog effects of UTP and diadenosine polyphosphates.

Adenosine triphosphate activates mitogen-activated protein kinase in human granulosa-luteal cells

ATP has been shown to activate the phospholipase C/diacylglycerol/protein kinase C (PKC) pathway. However, little is known about the downstream signaling events. The present study was designed to examine the effect of ATP on activation of the mitogen-activated protein kinase (MAPK) signaling pathway and its physiological role in human granulosa-luteal cells. Western blot analysis, using a monoclonal antibody that detected the phosphorylated forms of extracellular signal-regulated kinase-1 and -2 (p42(mapk) and p44 (mapk), respectively), demonstrated that ATP activated MAPK in a dose- and time-dependent manner. Treatment of the cells with suramin (a P2 purinoceptor antagonist), neomycin (a phospholipase C inhibitor), staurosporin (a PKC inhibitor), or PD98059 (an MAPK/ERK kinase inhibitor) significantly attenuated the ATP-induced activation of MAPK. In contrast, ATP-induced MAPK activation was not significantly affected by pertussis toxin (a G(i) inhibitor). To examine the role of G(s) protein, the intracellular cAMP level was determined after treatment with ATP or hCG. No significant elevation of intracellular cAMP was noted after ATP treatment. To determine the role of MAPK in steroidogenesis, human granulosa-luteal cells were treated with ATP, hCG, or ATP plus hCG in the presence or absence of PD98059. RIA revealed that ATP alone did not significantly affect the basal progesterone concentration. However, hCG-induced progesterone production was reduced by ATP treatment. PD98059 reversed the inhibitory effect of ATP on hCG-induced progesterone production. To our knowledge, this is the first demonstration of ATP-induced activation of the MAPK signaling pathway in the human ovary. These results support the idea that the MAPK signaling pathway is involved in mediating ATP actions in the human ovary.