Vasodilatation of intrapulmonary arteries to P2-receptor nucleotides in normal and pulmonary hypertensive newborn piglets

Endothelial pannexin 1-TRPV4 channel signaling lowers pulmonary arterial pressure in mice

Pannexin 1 (Panx1), an ATP-efflux pathway, has been linked with inflammation in pulmonary capillaries. However, the physiological roles of endothelial Panx1 in the pulmonary vasculature are unknown. Endothelial transient receptor potential vanilloid 4 (TRPV4) channels lower pulmonary artery (PA) contractility and exogenous ATP activates endothelial TRPV4 channels. We hypothesized that endothelial Panx1–ATP–TRPV4 channel signaling promotes vasodilation and lowers pulmonary arterial pressure (PAP). Endothelial, but not smooth muscle, knockout of Panx1 increased PA contractility and raised PAP in mice. Flow/shear stress increased ATP efflux through endothelial Panx1 in PAs. Panx1-effluxed extracellular ATP signaled through purinergic P2Y2 receptor (P2Y2R) to activate protein kinase Cα (PKCα), which in turn activated endothelial TRPV4 channels. Finally, caveolin-1 provided a signaling scaffold for endothelial Panx1, P2Y2R, PKCα, and TRPV4 channels in PAs, promoting their spatial proximity and enabling signaling interactions. These results indicate that endothelial Panx1–P2Y2R–TRPV4 channel signaling, facilitated by caveolin-1, reduces PA contractility and lowers PAP in mice.

Purinergic Dysfunction in Pulmonary Arterial Hypertension

Pulmonary arterial hypertension (PAH) is a life‐threatening disease characterized by increased pulmonary arterial pressure and pulmonary vascular resistance, which result in an increase in afterload imposed onto the right ventricle, leading to right heart failure. Current therapies are incapable of reversing the disease progression. Thus, the identification of novel and potential therapeutic targets is urgently needed. An alteration of nucleotide‐ and nucleoside‐activated purinergic signaling has been proposed as a potential contributor in the pathogenesis of PAH. Adenosine‐mediated purinergic 1 receptor activation, particularly A_2AR activation, reduces pulmonary vascular resistance and attenuates pulmonary vascular remodeling and right ventricle hypertrophy, thereby exerting a protective effect. Conversely, A_2BR activation induces pulmonary vascular remodeling, and is therefore deleterious. ATP‐mediated P2X₇R activation and ADP‐mediated activation of P2Y₁R and P2Y₁₂R play a role in pulmonary vascular tone, vascular remodeling, and inflammation in PAH. Recent studies have revealed a role of ectonucleotidase nucleoside triphosphate diphosphohydrolase, that degrades ATP/ADP, in regulation of pulmonary vascular remodeling. Interestingly, existing evidence that adenosine activates erythrocyte A_2BR signaling, counteracting hypoxia‐induced pulmonary injury, and that ATP release is impaired in erythrocyte in PAH implies erythrocyte dysfunction as an important trigger to affect purinergic signaling for pathogenesis of PAH. The present review focuses on current knowledge on alteration of nucleot(s)ide‐mediated purinergic signaling as a potential disease mechanism underlying the development of PAH.

Nitric Oxide-Dependent Feedback Loop Regulates Transient Receptor Potential Vanilloid 4 (TRPV4) Channel Cooperativity and Endothelial Function in Small Pulmonary Arteries

BACKGROUND

Recent studies demonstrate that spatially restricted, local Ca²⁺ signals are key regulators of endothelium-dependent vasodilation in systemic circulation. There are drastic functional differences between pulmonary arteries (PAs) and systemic arteries, but the local Ca²⁺ signals that control endothelium-dependent vasodilation of PAs are not known. Localized, unitary Ca²⁺ influx events through transient receptor potential vanilloid 4 (TRPV4) channels, termed TRPV4 sparklets, regulate endothelium-dependent vasodilation in resistance-sized mesenteric arteries via activation of Ca²⁺-dependent K⁺ channels. The objective of this study was to determine the unique functional roles, signaling targets, and endogenous regulators of TRPV4 sparklets in resistance-sized PAs.

METHODS AND RESULTS

Using confocal imaging, custom image analysis, and pressure myography in fourth-order PAs in conjunction with knockout mouse models, we report a novel Ca²⁺ signaling mechanism that regulates endothelium-dependent vasodilation in resistance-sized PAs. TRPV4 sparklets exhibit distinct spatial localization in PAs when compared with mesenteric arteries, and preferentially activate endothelial nitric oxide synthase (eNOS). Nitric oxide released by TRPV4-endothelial nitric oxide synthase signaling not only promotes vasodilation, but also initiates a guanylyl cyclase-protein kinase G-dependent negative feedback loop that inhibits cooperative openings of TRPV4 channels, thus limiting sparklet activity. Moreover, we discovered that adenosine triphosphate dilates PAs through a P2 purinergic receptor-dependent activation of TRPV4 sparklets.

CONCLUSIONS

Our results reveal a spatially distinct TRPV4-endothelial nitric oxide synthase signaling mechanism and its novel endogenous regulators in resistance-sized PAs.

Label-free electrochemical aptasensor for adenosine detection based on cascade signal amplification strategy

In this work, a simple and highly sensitive label-free electrochemical aptasensor for adenosine detection was developed based on target-aptamer binding triggered nicking endonuclease-assisted strand-replacement DNA polymerization and rolling circle amplification (RCA) strategy. The magnetic beads (MB) probe, which was attached the aptamer of adenosine and mDNA, was firstly fabricated. In the presence of adenosine, mDNA was released from MB upon recognition of the aptamer to target adenosine. The released mDNA as the primer activated autonomous DNA polymerization/nicking process and accompanied by the continuous release of replicated DNA fragments. Subsequently, numerous released DNA fragments were captured on the working electrode, and then as initiators to trigger the downstream RCA process leading to the formation of a long ssDNA concatemer for loading large amounts of Ru(NH₃)₆³⁺. Therefore, a conspicuously amplified electrochemical signal through the developed dual-amplification strategy could be achieved. This method exhibited a high sensitivity toward adenosine with a detection limit of 0.032nM. Also, it exhibited high selectivity to different nucleoside families and good reproducibility. This design opens new horizons for integrating different disciplines, presenting a versatile tool for ultrasensitive detecting organic small molecules in medical research and clinical diagnosis.

A fluorescent aptasensor using double-stranded DNA/graphene oxide as the indicator probe

We developed a fluorescent aptasensor based on the making use of double-stranded DNA (dsDNA)/graphene oxide (GO) as the signal probe and the activities of exonuclease I (Exo I). This method takes advantage of the stronger affinity of the aptamer to its target rather than to its complementary sequence (competitor), and the different interaction intensity of dsDNA, mononucleotides with GO. Specifically, in the absence of target, the competitor hybridizes with the aptamer, preventing the digestion of the competitor by Exo I, and thus the formed dsDNA is adsorbed on GO surface, allowing fluorescence quenching. When the target is introduced, the aptamer preferentially binds with its target. Thereby, the corresponding nuclease reaction takes place, and slight fluorescence change is obtained after the introduction of GO due to the weak affinity of the generated mononucleotides to GO. Adenosine (AD) was chosen as a model system and tested in detail. Under the optimized conditions, smaller dissociation constant (Kd, 311.0 µM) and lower detection limit (LOD, 3.1 µM) were obtained in contrast with traditional dye-labeled aptamer/GO based platform (Kd=688.8 µM, LOD=21.2 µM). Satisfying results were still obtained in the evaluation of the specificity and the detection of AD in human serum, making it a promising tool for the diagnosis of AD-relevant diseases. Moreover, we demonstrated the effect of the competitor on the LOD, and the results reveal that the sensitivity could be enhanced by using the rational competitor. The present design not only constructs a label-free aptamer based platform but also extends the application of dsDNA/GO complex in biochemical and biomedical studies.

Hairpin assembly circuit-based fluorescence cooperative amplification strategy for enzyme-free and label-free detection of small molecule

Here, we developed an enzyme-free, label-free, and sensitive fluorescence cooperative amplification strategy based on a hairpin assembly circuit which coupled catalytic hairpin assembly (CHA) with hybridization chain reaction (HCR) for small molecule adenosine. A double-strand DNA probe with aptamer-catalysis strand (Apt-C) and inhibit strand (Inh) was designed for adenosine recognition and signal transduction which was named as Apt-C/Inh. Hairpins H1 and H2 were employed for constructing the CHA, and hairpins H3 and H4 for the HCR. Through the binding of adenosine and the Apt-C, the Inh was released from the Apt-C/Inh. Then the free Apt-C initiated the CHA through successively opening H1 and H2, generating H1/H2 complex and recyclable Apt-C. Next, the released Apt-C entered another CHA cycle, and the H1/H2 complex further initiated the HCR of H3 and H4 which induced the formation of the concatemers of H3/H4 complex. Such a process brought the two ends of hairpins H3 into close proximity, yielding numerous integrated G-quadruplexes which were initially sequestered in the stem and two terminals of H3. Finally, N-methyl mesoporphyrin IX (NMM) was added to generate an enhanced fluorescence signal. In the proposed strategy, driven only by the energy from hybridization, one target could trigger multiple HCR events via CHA-based target-cycle, leading to a remarkable enzyme-free amplification for adenosine. The detection limit could achieve as low as 9.7 × 10(-7) mol L(-1). Furthermore, G-quadruplexes were applied to construct label-free hairpin assembly circuit, which made it more simple and cost-effective. The satisfactory recoveries were obtained when detecting adenosine in spiked human serum and urine samples, demonstrating the feasibility of this detection strategy in biological samples.

Small organic molecules detection based on aptamer-modified gold nanoparticles-enhanced quartz crystal microbalance with dissipation biosensor

Small molecules are difficult to detect by the conventional quartz crystal microbalance with dissipation (QCM-D) technique directly because the changes in frequency resulting from the binding processes of small biomolecules are often small. In the current study, an aptamer-based gold nanoparticles (AuNPs)-enhanced sensing strategy for detection of small molecules was developed. The QCM crystal was first modified with a layer of thiolated linker DNA, which can be partly base-paired with the detection part containing the adenosine aptamer sequence. In the presence of adenosine, the aptamer bound with adenosine and folded to the complex structure, which precluded the reporter part carrying AuNPs to combine with the random coiled detection part. Therefore, the lower the concentration of adenosine, the more AuNPs combined to the crystal. The resulting aptasensor showed a linear response to the increase of the adenosine concentration in the range of 0-2 μM with a linear correlation of r=0.99148 and a detection limit of 65 nM. Moreover, the aptasensor exhibited several excellent characteristics such as high sensitivity, selectivity, good stability, and reproducibility.

A novel enzyme-free and label-free fluorescence aptasensor for amplified detection of adenosine

A novel enzyme-free and label-free fluorescence aptasensor based on target-catalyzed hairpin self-assembly is developed for amplified detection of adenosine. This aptasensor contains four DNA strands termed as aptamer-catalysis strand, inhibit strand, hairpin structures H1 and H2 which are partially complementary. Meanwhile, a sequence that can form DNA G-quadruplex is partly hidden in the stem of H2. In the absence of adenosine, aptamer-catalysis strand is inhibited, and cannot trigger the self-assembly between H1 and H2. Upon the addition of adenosine, the binding event of aptamer and adenosine triggers the self-assembly between H1 and H2, resulting in the formation of G-quadruplex at the end of H1-H2 complex. The addition of N-methyl mesoporphyrin IX, which has a pronounced structural selectivity for G-quadruplex, generates label-free fluorescence signal. In the optimum conditions, we could detect adenosine as low as 6 μM by monitoring the change in fluorescence intensity. Furthermore, this amplified aptasensor shows high selectivity toward adenosine against its analogs due to the specific recognition ability of the aptamer for the target. Thus, the proposed aptasensor could be used as a simple and selective platform for target detection.

KF polymerase-based fluorescence aptasensor for the label-free adenosine detection

We have developed a simple, inexpensive, and label-free method for the selective detection of adenosine. Klenow fragment polymerase (KF polymerase) is a commonly-used 5' to 3' DNA polymerase, it also has 3' to 5' exonuclease activity that can digest single-stranded DNA. An adenosine binding DNA aptamer was employed, the aptamer was split into two pieces of single-stranded DNA (aptamer-A1 + aptamer-A2). Without the addition of adenosine, aptamer-A1 and aptamer-A2 existed as single-stranded DNA which could be efficiently degraded by the exonuclease activity of KF polymerase. Much reduced background fluorescence was obtained when SYBR Green dye was added. However, in the presence of adenosine, aptamer-A1 and aptamer-A2 bound to adenosine, and hybridization of the complementary sequences resulted in the formation of a duplex DNA structure, which could initiate DNA polymerization. The addition of SYBR Green dye resulted in a very high fluorescence enhancement, which could be used for the quantification of adenosine.

Time-resolved fluorescence biosensor for adenosine detection based on home-made europium complexes

In this protocol, the authors report a time-resolved fluorescence biosensor based on home-made europium complexes for highly sensitive detection of small molecules using adenosine as a model analyte. The fluorophore that used is europium complexes. Its signal can be measured in a time-resolved manner that eliminates most of the unspecific fluorescent background. The amino modified aptamer probe, which is designed to specifically recognize adenosine, is combined to the aldehyde-group modified glass slide by covalent bond. Europium complex-labeled a short ssDNA, designed to segment hybridize with aptamer probe is immobilized on the glass slide by hybridization reaction. In the presence of adenosine, the aptamer part is more inclined to bounds with adenosine and triggers structure-switching of the aptamer from aptamer/ssDNA duplex to aptamer/target complex. As a result, europium complexes-labeled ssDNA is forced to dissociate from the sensor interface, resulting in time-resolved fluorescence intensity decrease. The decrement intensity is proportional to the amount of adenosine. Under optimized assay conditions, a linear range (1.0×10(-8)M to 1.0×10(-7)M) is got with low detection limit of 5.61nM. The biosensor exhibits excellent selectivity and can provide a promising potential for aptamer-based adenosine detection.

Blank peak current-suppressed electrochemical aptameric sensing platform for highly sensitive signal-on detection of small molecule

In this contribution, an electrochemical aptameric sensing scheme for the sensitive detection of small molecules is proposed using adenosine as a target model. A ferrocene (Fc)-functionalized thiolated aptamer probe is adapted and immobilized onto an electrode surface. Introducing a recognition site for EcoRI into the aptamer sequence not only suppresses the peak current corresponding to blank sample but also provides a signal-on response mechanism. In the absence of adenosine, the aptamer can fold into a hairpin structure and form a cleavable double-stranded region. Fc is capable of being removed from electrode surface by treatment with endonuclease, and almost no peak current is observed. The adenosine/aptamer binding induces the conformational transition of designed aptamer, dissociating the cleavable double-stranded segment. Therefore, the integrated aptamer sequence is maintained when exposing to endonuclease, generating a peak current of Fc. Utilizing the present sensing scheme, adenosine even at a low concentration can give a detectable current signal. Thus, a detection limit of 10⁻¹⁰ M and a linear response range from 3.74 × 10⁻⁹ to 3.74 × 10⁻⁵ M are achieved. The proposed proof-of-principle of a novel electrochemical sensing is expected to extend to establish various aptameric platforms for the analysis of a broad range of target molecules of interest.

A solid-state electrochemiluminescence sensing platform for detection of adenosine based on ferrocene-labeled structure-switching signaling aptamer

A solid-state electrochemiluminescence sensing platform based on ferrocene-labeled structure-switching signaling aptamer (Fc-aptamer) for highly sensitive detection of small molecules is developed successfully using adenosine as a model analyte. Such special sensing platform included two main parts, an electrochemiluminescence (ECL) substrate and an ECL intensity switch. The ECL substrate was made by modifying the complex of Au nanoparticle and Ruthenium (II) tris-(bipyridine) (Ru(bpy)(3)(2+)-AuNPs) onto Au electrode. An anti-adenosine aptamer labeled by ferrocene acted as the ECL intensity switch. A short complementary ssDNA for the aptamer was applied to hybridizing with the aptamer, yielding a double-stranded complex of the aptamer and the ssDNA on the electrode surface. The introduction of adenosine triggered structure switching of the aptamer. As a result, the ssDNA was forced to dissociate from the sensing platform. Such structural change of the aptamer resulted in an obvious ECL intensity decrease due to the increased quenching effect of Fc to the ECL substrate. The analytic results were sensitive and specific.

ATP-induced vasodilation and purinergic receptors in the human leg: roles of nitric oxide, prostaglandins, and adenosine

Plasma ATP is thought to contribute to the local regulation of skeletal muscle blood flow. Intravascular ATP infusion can induce profound limb muscle vasodilatation, but the purinergic receptors and downstream signals involved in this response remain unclear. This study investigated: 1) the role of nitric oxide (NO), prostaglandins, and adenosine as mediators of ATP-induced limb vasodilation and 2) the expression and distribution of purinergic P(2) receptors in human skeletal muscle. Systemic and leg hemodynamics were measured before and during 5-7 min of femoral intra-arterial infusion of ATP [0.45-2.45 micromol/min] in 19 healthy male subjects with and without coinfusion of N(G)-monomethyl-l-arginine (l-NMMA; NO formation inhibitor; 12.3 +/- 0.3 (SE) mg/min), indomethacin (INDO; prostaglandin formation blocker; 613 +/- 12 microg/min), and/or theophylline (adenosine receptor blocker; 400 +/- 26 mg). During control conditions, ATP infusion increased leg blood flow (LBF) from baseline conditions by 1.82 +/- 0.14 l/min. When ATP was coinfused with either l-NMMA, INDO, or l-NMMA + INDO combined, the increase in LBF was reduced by 14 +/- 6, 15 +/- 9, and 39 +/- 8%, respectively (all P < 0.05), and was associated with a parallel lowering in leg vascular conductance and cardiac output and a compensatory increase in leg O(2) extraction. Infusion of theophylline did not alter the ATP-induced leg hyperemia or systemic variables. Real-time PCR analysis of the mRNA content from the vastus lateralis muscle of eight subjects showed the highest expression of P(2Y2) receptors of the 10 investigated P(2) receptor subtypes. Immunohistochemistry showed that P(2Y2) receptors were located in the endothelium of microvessels and smooth muscle cells, whereas P(2X1) receptors were located in the endothelium and the sacrolemma. Collectively, these results indicate that NO and prostaglandins, but not adenosine, play a role in ATP-induced vasodilation in human skeletal muscle. The expression and localization of the nucleotide selective P(2Y2) and P(2X1) receptors suggest that these receptors may mediate ATP-induced vasodilation in skeletal muscle.

Changes in purinergic signalling in developing and ageing rat tail artery: importance for temperature control

This study aimed to examine the expression and function of P2 receptors of the rat tail and mesenteric arteries during maturation and ageing (4, 6 and 12 weeks, 8 and 24 months). Functional studies and receptor expression by immunohistochemistry revealed a heterogeneous phenotype of P2 receptor subtypes depending on artery age. The purinergic component of nerve-mediated responses in the tail artery was greater in younger animals; similarly responses to ATP and alpha,beta-meATP and the expression of P2X1 receptors decreased with age. Contractile responses to 2-MeSADP decreased with age, and were absent at 8 and 24 months; P2Y1 receptor expression followed this pattern. UTP-induced contractions and P2Y2 receptor expression also decreased with age. The mesenteric artery contracted to UTP, responses at 4 and 6 weeks were larger than at other ages although P2Y2 receptor expression did not significantly differ with age. 2-MeSADP induced relaxation of the mesenteric artery, responses being greatest at 6 weeks and decreased thereafter, which was mimicked by the P2Y1 receptor immunostaining. We speculate that the dramatic changes in expression of P2 receptors in the rat tail artery, compared to the mesenteric artery, during development and ageing are related to the role of the tail artery in temperature regulation.

Acidosis abolishes the effect of repeated applications of ATP on pulmonary artery force and [Ca2+]i

The purine nucleotide, ATP, can cause receptor-mediated desensitizing contractions of smooth muscle that may be modulated by pH. We investigated in the rat the effect of acidosis upon the contractile and Ca2+ responses induced by ATP upon intrapulmonary artery (PA) smooth muscle. Four successive applications of ATP (300 microM) at pH 7.4 induced desensitising contractile responses that showed progressively decreasing peak amplitudes that correlated with decreases of [Ca2+]i. Acidosis significantly reduced the peak contractile response to the first application of ATP without modifying the rate or degree of desensitisation in response to ATP and without decreasing the [Ca2+]i. Successive applications of ATP did not further reduce contractile force nor [Ca2+]i. These results demonstrated that acidosis abolishes the effect of repeat applications of ATP on pulmonary artery force and [Ca2+]i via alteration in the desensitization-resensitisation characteristics of ATP receptor. This suggest a potentially important physiological role for changes in external pH in the regulation of ATP-mediated control of the pulmonary circulation.

P2Y purine receptor responses and expression in the pulmonary circulation of juvenile rabbits

The purine nucleotide ATP mediates pulmonary vasodilation at birth by stimulation of P2Y purine receptors in the pulmonary circulation. The specific P2Y receptors in the pulmonary circulation and the segmental distribution of their responses remain unknown. We investigated the effects of purine nucleotides, ATP, ADP, and AMP, and pyrimidine nucleotides, UTP, UDP, and UMP, in juvenile rabbit pulmonary arteries for functional characterization of P2Y receptors. We also studied the expression of P2Y receptor subtypes in pulmonary arteries and the role of nitric oxide (NO), prostaglandins, and cytochrome P-450 metabolites in the response to ATP. In conduit size arteries, ATP, ADP, and AMP caused greater relaxation responses than UTP, UDP, and UMP. In resistance vessels, ATP and UTP caused comparable vasodilation. The response to ATP was attenuated by the P2Y antagonist cibacron blue, the NO synthase antagonist N(omega)-nitro-l-arginine methyl ester (l-NAME), and the cytochrome P-450 inhibitor 17-octadecynoic acid but not by the P2X antagonist alpha,beta-methylene ATP or the cyclooxygenase inhibitor indomethacin in conduit arteries. In the resistance vessels, l-NAME caused a more complete inhibition of the responses to ATP and UTP. Responses to AMP and UMP were NO and endothelium dependent, whereas responses to ADP and UDP were NO and endothelium independent in the conduit arteries. RT-PCR showed expression of P2Y(1), P2Y(2), and P2Y(4) receptors, but not P2Y(6) receptors, in lung parenchyma, pulmonary arteries, and pulmonary artery endothelial cells. These data suggest that distinct P2Y receptors mediate the vasodilator responses to purine and pyrimidine nucleotides in the juvenile rabbit pulmonary circulation. ATP appears to cause NO-mediated vasodilation predominantly through P2Y2 receptors on endothelium.

ATP-induced vasodilation in human skeletal muscle

1. The purine nucleotide adenosine-5'-triphosphate (ATP) exerts pronounced effects on the cardiovascular system. The mechanism of action of the vasodilator response to ATP in humans has not been elucidated yet. The proposed endothelium-derived relaxing factors (EDRFs) were studied in a series of experiments, using the perfused forearm technique. 2. Adenosine 5'-triphosphate (0.2, 0.6, 6 and 20 nmol dl(-1) forearm volume min(-1)) evoked a dose-dependent forearm vasodilator response, which could not be inhibited by separate infusion of the nonselective COX inhibitor indomethacin (5 microg dl(-1) min(-1), n=10), the blocker of Na(+)/K(+)-ATPase ouabain (0.2 microg dl(-1) min(-1), n=8), the blocker of K(Ca) channels tetraethylammonium chloride (TEA, 0.1 microg dl(-1) min(-1), n=10), nor by the K(ATP)-channel blocker glibenclamide (2 microg dl(-1) min(-1), n=10). All blockers, except glibenclamide, caused a significant increase in baseline vascular tone. The obtained results might be due to compensatory actions of unblocked EDRFs. Combined infusion of TEA, indomethacin and l-NMMA (n=6) significantly increased the baseline forearm vascular resistance. The ATP-induced relative decreases in forearm vascular resistance were 48+/-5, 67+/-3, 88+/-2, and 92+/-2% in the absence and 23+/-7, 62+/-4, 89+/-2, and 93+/-1% in the presence of the combination of TEA, indomethacin and l-NMMA (P<0.05, repeated-measures ANOVA, n=6). A similar inhibition was obtained for sodium nitroprusside (SNP, P<0.05 repeated-measures ANOVA, n=6), indicating a nonspecific interaction due to the blocker-induced vasoconstriction. 3. ATP-induced vasodilation in the human forearm cannot be inhibited by separate infusion of indomethacin, ouabain, glibenclamide or TEA, or by a combined infusion of TEA, indomethacin, and l-NMMA. Endothelium-independent mechanisms and involvement of unblocked EDRFs, such as CO, might play a role, and call for further studies.

Extracellular ATP-mediated signaling for survival in hyperoxia-induced oxidative stress

Respiratory failure is a serious consequence of lung cell injury caused by treatment with high inhaled oxygen concentrations. Human lung microvascular endothelial cells (HLMVEC) are a principal target of hyperoxic injury (hyperoxia). Cell stress can cause release of ATP, and this extracellular nucleotide can activate purinoreceptors and mediate responses essential for survival. In this investigation, exposure of endothelial cells to an oxidative stress, hyperoxia, caused rapid but transient ATP release (20.03 +/- 2.00 nm/10(6) cells in 95% O(2) versus 0.08 +/- 0.01 nm/10(6) cells in 21% O2 at 30 min) into the extracellular milieu without a concomitant change in intracellular ATP. Endogenously produced extracellular ATP-enhanced mTOR-dependent uptake of glucose (3467 +/- 102 cpm/mg protein in 95% oxygen versus 2100 +/- 112 cpm/mg protein in control). Extracellular addition of ATP-activated important cell survival proteins like PI 3-kinase and extracellular-regulated kinase (ERK-1/2). These events were mediated primarily by P2Y receptors, specifically the P2Y2 and/or P2Y6 subclass of receptors. Extracellular ATP was required for the survival of HLMVEC in hyperoxia (55 +/- 10% surviving cells with extracellular ATP scavengers [apyrase + adenosine deaminase] versus 95 +/- 12% surviving cells without ATP scavengers at 4 d of hyperoxia). Incubation with ATP scavengers abolished ATP-dependent ERK phosphorylation stimulated by hyperoxia. Further, ERK activation also was found to be important for cell survival in hyperoxia, as treatment with PD98059 enhanced hyperoxia-mediated cell death. These findings demonstrate that ATP release and subsequent ATP-mediated signaling events are vital for survival of HLMVEC in hyperoxia.

A three-enzyme microelectrode sensor for detecting purine release from central nervous system

As the purines, in particular adenosine, are important signaling agents in the nervous system we have devised a new biosensor for directly measuring their production in real time during physiological activity. Our amperometric adenosine biosensor is made by entrapping 3 enzymes (xanthine oxidase, purine nucleoside phosphorylase and adenosine deaminase) in a composite lactobionamide and amphiphillic polypyrrole matrix around a Pt microelectrode. The resulting sensors are small (25-100 microm diameter), fast responding (10-90% rise time, 2+/-0.23 s), sensitive (100-222 mA M(-1) cm(-2)) and stable (100% activity after 5 days). The sensor was used in vivo to demonstrate the spatial localization of release of adenosine from Xenopus embryo spinal cord during fictive swimming.