bluuebunny/crossref_metadata_2025 huggingface dataset:
Automatic verification of safety and liveness for pipelined machines using WEB refinement
Authors: Manolios Panagiotis , Srinivasan Sudarshan K.
Published: July 2008

We show how to automatically verify that complex pipelined machine models satisfy the same safety and liveness properties as their instruction-set architecture (ISA) models by using well-founded equivalence bisimulation (WEB) refinement. We show how to reduce WEB-refinement proof obligations to formulas expressible in the decidable logic of counter arithmetic with lambda expressions and uninterpreted functions (CLU). This allows us to automate the verification of the pipelined machine models by using the UCLID decision procedure to transform CLU formulas to Boolean satisfiability problems. To relate pipelined machine states to ISA states, we use the commitment and flushing refinement maps. We evaluate our work using 17 pipelined machine models that contain various features, including deep pipelines, precise exceptions, branch prediction, interrupts, and instruction queues. Our experimental results show that the overhead of proving liveness, obtained by comparing the cost of proving both safety and liveness with the cost of only proving safety, is about 17%, but depends on the refinement map used; for example, the liveness overhead is 23% when flushing is used and is negligible when commitment is used.
ILP-Based energy minimization techniques for banked memories
Authors: Ozturk Ozcan , Kandemir Mahmut
Published: July 2008

Main memories can consume a significant portion of overall energy in many data-intensive embedded applications. One way of reducing this energy consumption is banking, that is, dividing available memory space into multiple banks and placing unused (idle) memory banks into low-power operating modes. Prior work investigated code-restructuring- and data-layout-reorganization-based approaches for increasing the energy benefits that could be obtained from a banked memory architecture. This article explores different techniques that can potentially coexist within the same optimization framework for maximizing benefits of low-power operating modes. These techniques include employing nonuniform bank sizes, data migration, data compression, and data replication. By using these techniques, we try to increase the chances for utilizing low-power operating modes in a more effective manner, and achieve further energy savings over what could be achieved by exploiting low-power modes alone. Specifically, nonuniform banking tries to match bank sizes with application-data access patterns. The goal of data migration is to cluster data with similar access patterns in the same set of banks. Data compression reduces the size of the data used by an application, and thus helps reduce the number of memory banks occupied by data. Finally, data replication increases bank idleness by duplicating select read-only data blocks across banks. We formulate each of these techniques as an ILP (integer linear programming) problem, and solve them using a commercial solver. Our experimental analysis using several benchmarks indicates that all the techniques presented in this framework are successful in reducing memory energy consumption. Based on our experience with these techniques, we recommend to compiler writers for banked memories to consider data compression, replication, and migration.
Optimal vertex elimination in single-expression-use graphs
Authors: Naumann Uwe , Hu Yuxiao
Published: July 2008

The source transformation tool for automatic differentiation of Fortran programs ADIFOR uses a preaccumulation technique to speed up tangent-linear codes significantly compared to the standard forward mode. Reverse mode automatic differentiation is applied to all scalar assignments to generate efficient code for the computation of local gradients. It has been well known for some time that reverse mode is not necessarily the optimal choice for the computation of these statement-level gradients as it does not minimize the number of operations required. This article presents an efficient algorithm for the solution of this combinatorial optimization problem. The corresponding software is freely available for downloading on our website. Developers of software for automatic differentiation are invited to integrate the algorithm into their tools.

Gradients of scalar multivariate functions can be computed by elimination methods on the linearized computational graph. The combinatorial optimization problem that aims to minimize the number of arithmetic operations performed by the elimination algorithm is known to be NP-complete. In this article we present a polynomial algorithm for solving a relevant subclass of this problem's instances. The proposed method relies on the ability to compute vertex covers in bipartite graphs in polynomial time. A simplified version of this graph algorithm is used in a research prototype of the differentiation-enabled NAGWare Fortran compiler for the preaccumulation of local gradients of scalar assignments in the context of automatic generation of efficient tangent-linear code for numerical programs.
Families of algorithms related to the inversion of a Symmetric Positive Definite matrix
Authors: Bientinesi Paolo , Gunter Brian , Geijn Robert A. van de
Published: July 2008

We study the high-performance implementation of the inversion of a Symmetric Positive Definite (SPD) matrix on architectures ranging from sequential processors to Symmetric MultiProcessors to distributed memory parallel computers. This inversion is traditionally accomplished in three “sweeps”: a Cholesky factorization of the SPD matrix, the inversion of the resulting triangular matrix, and finally the multiplication of the inverted triangular matrix by its own transpose. We state different algorithms for each of these sweeps as well as algorithms that compute the result in a single sweep. One algorithm outperforms the current ScaLAPACK implementation by 20-30 percent due to improved load-balance on a distributed memory architecture.
Algorithm 880
Authors: Marques Osni A. , Vömel Christof , Demmel James W. , Parlett Beresford N.
Published: July 2008

LAPACK is often mentioned as a positive example of a software library that encapsulates complex, robust, and widely used numerical algorithms for a wide range of applications. At installation time, the user has the option of running a (limited) number of test cases to verify the integrity of the installation process. On the algorithm developer's side, however, more exhaustive tests are usually performed to study algorithm behavior on a variety of problem settings and also computer architectures. In this process, difficult test cases need to be found that reflect particular challenges of an application or push algorithms to extreme behavior. These tests are then assembled into a comprehensive collection, therefore making it possible for any new or competing algorithm to be stressed in a similar way. This article describes an infrastructure for exhaustively testing the symmetric tridiagonal eigensolvers implemented in LAPACK. It consists of two parts: a selection of carefully chosen test matrices with particular idiosyncrasies and a portable testing framework that allows for easy testing and data processing. The tester facilitates experiments with algorithmic choices, parameter and threshold studies, and performance comparisons on different architectures.
SNOBFIT -- Stable Noisy Optimization by Branch and Fit
Authors: Huyer Waltraud , Neumaier Arnold
Published: July 2008

The software package SNOBFIT for bound-constrained (and soft-constrained) noisy optimization of an expensive objective function is described. It combines global and local search by branching and local fits. The program is made robust and flexible for practical use by allowing for hidden constraints, batch function evaluations, change of search regions, etc.
Benchmarking Domain-Specific Compiler Optimizations for Variational Forms
Authors: Kirby Robert C. , Logg Anders
Published: July 2008

We examine the effect of using complexity-reducing relations [Kirby et al. 2006] to generate optimized code for the evaluation of finite-element variational forms. The optimizations are implemented in a prototype code named FErari, which has been integrated as an optimizing backend to the FEniCS form compiler, FFC [Kirby and Logg 2006; 2007]. In some cases, FErari provides very little speedup, while in other cases we obtain reduced local operation counts by a factor of as much as 7.9 and speedups for the assembly of the global sparse matrix by as much as a factor of 2.8 (see Figure 9).
Access for all
Authors: Aycinena Peggy
Published: July 2008

Accessible technologies are improving the lives of millions of physically impaired people around the world.
ViewpointEnvisioning the future of computing research
Authors: Lazowska Ed
Published: July 2008

Advances in computing have changed our lives---the Computing Community Consortium aims to help the research community continue that lineage.
Scaling in games and virtual worlds
Authors: Waldo Jim
Published: July 2008

Online games and virtual worlds have familiar scaling requirements, but don't be fooled: Everything you know is wrong.
Designing games with a purpose
Authors: von Ahn Luis , Dabbish Laura
Published: July 2008

Data generated as a side effect of game play also solves computational problems and trains AI algorithms.
Reasoning in symbolic computation
Authors: Barnett Michael P.
Published: July 2008

I discuss notations for some styles of mathematical reasoning that include analogy. These notations extend the conventions of the mathematical package mathscape that I reported recently in the Journal of Symbolic Computation. The paper introduces the reasoning objects that I call "precursors" and "consequences lists".
ACM 2007 Kanellakis Award Honours Bruno Buchberger Innovator of Automated Tools for Mathematics
Authors: Giesbrecht Mark
Published: July 2008

SIGSAM is pleased to announce that Bruno Buchberger of the Research Institute for Symbolic Computation (RISC) at Johannes Kepler University in Linz, Austria, has been awarded the 2007 ACM Paris Kanellakis Theory and Practice Award. This is one of the ACM's top prizes and recognizes his role in developing Gröbner bases. We congratulate Bruno for this outstanding achievement and honour!
Open source computer algebra systems
Authors: Joyner David
Published: July 2008

This survey will look at Axiom, a free and very powerful computer algebra system available. It is a general purpose CAS useful for symbolic computation, research, and the development of new mathematical algorithms. Axiom is similar in some ways to Maxima, covered in the survey [J1], but different in many ways as well. Axiom, Maxima, and SAGE [S], are the largest of the general-purpose open-source CAS's. If you want to "take a test drive," Axiom can be tested without installation via the web interface [AS] or the SAGE online interface [S].
How to cleverly count pattern-avoiding words (abstract only)
Authors: Pudwell Lara K.
Published: July 2008

A word w contains a permutation p as a pattern if w has a subsequence that is order-isomorphic to p; otherwise, w avoids p. The study of pattern avoidance in permutations is well-studied and has been accomplished by many beautiful techniques. In 1998, Doron Zeilberger introduced the notion of prefix schemes for counting pattern-avoiding permutations. This is a divide and conquer technique driven by the pattern formed by the first few letters of the permutation. I will discuss one way of extending the method of prefix schemes to enumerate pattern-avoiding words and detail its success rate.
Computer-generated conjectures(!) and proofs(!!) in combinatorial game theory (abstract only)
Authors: Zeilberger Doron , Thanatipanonda Thotsaporn "Aek"
Published: July 2008

The rapidly growing activity of experimental mathematics is still, to a large extent, a straightforward (albeit far-reaching) extension of the usual mode of paper-and-pencil research, where the pencil just got so much quicker and sharper and the paper so much larger. In order to take full advantage of the great potential of computers, we should learn to kick some old habits, like trying to "understand" what is going on. If we humans can "understand" something, then it can't be very deep. Rather than try to understand mathematics, we should do our best to meta-understand it, by designing algorithms (and meta-algorithms!) for computers to do everything by themselves: generating data, of course, but then going on to formulate conjectures, followed by (fully automated!) proofs. We admit that our computers can't prove the Riemann Hypothesis yet, but they sure can prove some intriguing conjectures of Jeff Erickson about the game "Toads and Frogs". The only way our computers can prove these simply stated (i.e. "beautiful" to human eyes) conjectures, is by making many other "ugly" (to humans) conjectures, and then proving them simultaneously. The full details are available from www.math.rutgers.edu/~zeilberg/mamarim/mamarimhtml/tf1.html.
Enumerating the Saneblidze-Umble diagonal in Haskell (abstract only)
Authors: Vejdemo-Johansson Mikael
Published: July 2008

In 2004, Saneblidze and Umble gave a construction of a diagonal on the permutahedron, thus providing important tools to several disciplines using the permutahedra and associated combinatorial polyhedra. There has since been a few, mostly unpublished, attempts at writing computer programs to perform the highly combinatorial construction. The author presents an implementation of the construction in the programming language Haskell: a language which allows one to write computer code that stays very close to the mathematical expression of the construction itself. The author wishes to emphasize the perceived naturality of translating mathematics into Haskell code by giving examples from this program. (Received July 25, 2007.
GeometryEditor
Authors: Lai Xun , Wang Paul S.
Published: July 2008

GeometryEditor (previous code name: GeoSVG) is a Web-based environment for authoring interactive geometry manipulatives. Users may create on-line manipulatives to illustrate mathematical concepts for a hands-on learning environment. GeometryEditor provides standard authoring features, such as sketching, measurements, calculation, macros, iteration, loci, animation and coordinate systems. GeometryEditor also offers several its own authoring features, such as synchronized copy, parametric color and visibility, and mouse click events.

The GeoSite provides the GeometryEditor authoring environment and a corresponding page authoring environment to assist in creating lessons around the manipulatives. Other people via the Internet can immediately view completed manipulatives and pages.
Detecting polynomial perfect powers (abstract only)
Authors: Roche Daniel , Giesbrecht Mark
Published: July 2008

We consider the problem of determining whether a polynomial f is a perfect power of another polynomial h, i.e. whether f = hr for some integer r > 0. In particular, we seek algorithms which take advantage of the sparsity in f, and so will be fast when the input is lacunary, with only the nonzero terms represented. We give such algorithms, for polynomials with finite field or rational coefficients, after first showing that in any non-trivial case the power r must be small. An implementation is given in the C++ library NTL, and we compare our results to the fastest-known "dense" algorithm.
Distributed Computing Economics
Authors: Gray Jim
Published: July 2008

Computing is free. The world’s most powerful computer is free (SETI@Home is a 54-teraflop machine). Google freely provides a trillion searches per year to the world’s largest online database (two petabytes). Hotmail freely carries a trillion e-mail messages per year. Amazon.com offers a free book-search tool. Many sites offer free news and other free content. Movies, sports events, concerts, and entertainment are freely available via television.
A Conversation with Erik Meijer and Jose Blakeley
Authors: Coatta Terry
Published: July 2008

To understand more about LINQ and ORM and why Microsoft took this approach, we invited two Microsoft engineers closely involved with their development, Erik Meijer and Jos Blakeley, to speak with Queue editorial board member Terry Coatta.
Exposing the ORM Cache
Authors: Keith Michael , Stafford Randy
Published: July 2008

In the early 1990s, when object-oriented languages emerged into the mainstream of software development, a noticeable surge in productivity occurred as developers saw new and better ways to create software programs. Although the new and efficient object programming paradigm was hailed and accepted by a growing number of organizations, relational database management systems remained the preferred technology for managing enterprise data. Thus was born ORM (object-relational mapping), out of necessity, and the complex challenge of saving the persistent state of an object environment in a relational database subsequently became known as the object-relational impedance mismatch.
Charged Lepton Flavor Violation Experiments
Authors: Marciano William J. , Mori Toshinori , Roney J. Michael
Published: July 2008

We provide a review of the status of experimental searches for lepton flavor violation involving electrons, muons, and tau leptons. Future experimental programs are discussed and placed in the context of theories beyond the standard model.
Changes in the structure-function relationship of elastin and its impact on the proximal pulmonary arterial mechanics of hypertensive calves
Authors: Lammers Steven R. , Kao Phil H. , Qi H. Jerry , Hunter Kendall , Lanning Craig , Albietz Joseph , Hofmeister Stephen , Mecham Robert , Stenmark Kurt R. , Shandas Robin
Published: July 2008

Extracellular matrix remodeling has been proposed as one mechanism by which proximal pulmonary arteries stiffen during pulmonary arterial hypertension (PAH). Although some attention has been paid to the role of collagen and metallomatrix proteins in affecting vascular stiffness, much less work has been performed on changes in elastin structure-function relationships in PAH. Such work is warranted, given the importance of elastin as the structural protein primarily responsible for the passive elastic behavior of these conduit arteries. Here, we study structure-function relationships of fresh arterial tissue and purified arterial elastin from the main, left, and right pulmonary artery branches of normotensive and hypoxia-induced pulmonary hypertensive neonatal calves. PAH resulted in an average 81 and 72% increase in stiffness of fresh and digested tissue, respectively. Increase in stiffness appears most attributable to elevated elastic modulus, which increased 46 and 65%, respectively, for fresh and digested tissue. Comparison between fresh and digested tissues shows that, at 35% strain, a minimum of 48% of the arterial load is carried by elastin, and a minimum of 43% of the change in stiffness of arterial tissue is due to the change in elastin stiffness. Analysis of the stress-strain behavior revealed that PAH causes an increase in the strains associated with the physiological pressure range but had no effect on the strain of transition from elastin-dominant to collagen-dominant behavior. These results indicate that mechanobiological adaptations of the continuum and geometric properties of elastin, in response to PAH, significantly elevate the circumferential stiffness of proximal pulmonary arterial tissue.
Infarct limitation by a protein kinase G activator at reperfusion in rabbit hearts is dependent on sensitizing the heart to A2b agonists by protein kinase C
Authors: Kuno Atsushi , Solenkova Nataliya V. , Solodushko Victoriya , Dost Turhan , Liu Yanping , Yang Xi-Ming , Cohen Michael V. , Downey James M.
Published: July 2008

PKG activator 8-(4-chlorophenylthio)-guanosine 3′,5′-cyclic monophosphate (CPT) at reperfusion protects ischemic hearts, but the mechanism is unknown. We recently proposed that in preconditioned hearts PKC lowers the threshold for adenosine to initiate signaling from low-affinity A2b receptors during early reperfusion thus allowing endogenous adenosine to activate survival kinases phosphatidylinositol 3-kinase (PI3K) and ERK. We tested whether CPT might also sensitize A2b receptors to adenosine. CPT (10 μM) during the first minutes of reperfusion markedly reduced infarction in isolated rabbit hearts undergoing 30-min regional ischemia/2-h reperfusion, and salvage was blocked by MRS 1754, an A2b-selective antagonist. Coadministration of wortmannin (PI3K inhibitor) or PD-98059 (MEK1/2 and therefore ERK1/2 inhibitor) also blocked protection. In nonischemic hearts, 10-min infusion of CPT did not change phosphorylation of Akt or ERK1/2. Neither did a subthreshold dose (2.5 nM) of the nonselective but A2b-potent receptor agonist 5′-( N-ethylcarboxamido)adenosine (NECA). However, when 2.5 nM NECA was combined with 10 μM CPT, both phospho-Akt and phospho-ERK1/2 significantly increased, indicating CPT had lowered the threshold for A2b-dependent signaling. The PKC antagonist chelerythrine blocked this phosphorylation induced by CPT + NECA. Chelerythrine also blocked the anti-infarct effect of CPT as did nonselective (glibenclamide) and mitochondrial-selective (5-hydroxydecanoate) KATP channel blockers. A free radical scavenger, N-(2-mercaptopropionyl)glycine, also blocked CPT protection. We propose CPT targets PKG, which activates PKC through mitochondrial KATP channel (mitoKATP)-dependent redox signaling, a sequence mimicking that already documented in preconditioning. Activated PKC then augments sensitivity of normally low-affinity cardiac adenosine A2b receptors so endogenous adenosine can protect by activating Akt and ERK.
Helicobacter pylori-induced inhibition of vascular endothelial cell functions: a role for VacA-dependent nitric oxide reduction
Authors: Tobin Nicholas P. , Henehan Gary T. , Murphy Ronan P. , Atherton John C. , Guinan Anthony F. , Kerrigan Steven W. , Cox Dermot , Cahill Paul A. , Cummins Philip M.
Published: July 2008

Epidemiological and clinical studies provide compelling support for a causal relationship between Helicobacter pylori infection and endothelial dysfunction, leading to vascular diseases. However, clear biochemical evidence for this association is limited. In the present study, we have conducted a comprehensive investigation of endothelial injury in bovine aortic endothelial cells (BAECs) induced by H. pylori-conditioned medium (HPCM) prepared from H. pylori 60190 [vacuolating cytotoxin A (Vac+)]. BAECs were treated with either unconditioned media, HPCM (0–25% vol/vol), or Escherichia coli-conditioned media for 24 h, and cell functions were monitored. Vac+HPCM significantly decreased BAEC proliferation, tube formation, and migration (by up to 44%, 65%, and 28%, respectively). Posttreatment, we also observed sporadic zonnula occludens-1 immunolocalization along the cell-cell border, and increased BAEC permeability to FD40 Dextran, indicating barrier reduction. These effects were blocked by 5-nitro-2-(3-phenylpropylamino)benzoic acid (VacA inhibitor) and were not observed with conditioned media prepared from either VacA-deleted H. pylori or E. coli. The cellular mechanism mediating these events was also considered. Vac+HPCM (but not Vac−) reduced nitric oxide (NO) by >50%, whereas S-nitroso- N-acetylpenicillamine, an NO donor, recovered all Vac+HPCM-dependent effects on cell functions. We further demonstrated that laminar shear stress, an endothelial NO synthase/NO stimulus in vivo, could also recover the Vac+HPCM-induced decreases in BAEC functions. This study shows, for the first time, a significant proatherogenic effect of H. pylori-secreted factors on a range of vascular endothelial dysfunction markers. Specifically, the VacA-dependent reduction in endothelial NO is indicated in these events. The atheroprotective impact of laminar shear stress in this context is also evident.
Endogenous hydrogen sulphide mediates the cardioprotection induced by ischemic postconditioning
Authors: Yong Qian Chen , Lee Shiau Wei , Foo Chun Shin , Neo Kay Li , Chen Xin , Bian Jin-Song
Published: July 2008

The present study aimed to investigate the role of hydrogen sulphide (H2S) in the cardioprotection induced by ischemic postconditioning and to examine the underlying mechanisms. Cardiodynamics and myocardial infarction were measured in isolated rat hearts. Postconditioning with six episodes of 10-s ischemia (IPostC) significantly improved cardiodynamic function, which was attenuated by the blockade of endogenous H2S production with d-l-propargylglycine. Moreover, IPostC significantly stimulated H2S synthesis enzyme activity during the early period of reperfusion. However, d-l-propargylglycine only attenuated the IPostC-induced activation of PKC-α and PKC-ε but not that of PKC-δ, Akt, and endothelial nitric oxide synthase (eNOS). These data suggest that endogenous H2S contributes partially to the cardioprotection of IPostC via stimulating PKC-α and PKC-ε. Postconditioning with six episodes of a 10-s infusion of NaHS (SPostC) or 2 min continuous NaHS infusion (SPostC2) stimulated activities of Akt and PKC, improved the cardiodynamic performances, and reduced myocardial infarct size. The blockade of Akt with LY-294002 (15 μM) or PKC with chelerythrine (10 μM) abolished the cardioprotection induced by H2S postconditioning. SPostC2, but not SPostC, also additionally stimulated eNOS. We conclude that endogenous H2S contributes to IPostC-induced cardioprotection. H2S postconditioning confers the protective effects against ischemia-reperfusion injury through the activation of Akt, PKC, and eNOS pathways.
Femoral artery occlusion augments TRPV1-mediated sympathetic responsiveness
Authors: Xing Jihong , Gao Zhaohui , Lu Jian , Sinoway Lawrence I. , Li Jianhua
Published: July 2008

Muscle metabolic by-products stimulate thin fiber muscle afferent nerves and evoke reflex increases in blood pressure and sympathetic nerve activity. Previous studies reported that chemically sensitive transient receptor potential vanilloid type 1 (TRPV1) channels present on sensory muscle afferent neurons have an important impact on sympathetically mediated cardiovascular responses. The reflex-mediated reduction in blood flow to skeletal muscle leads to limited exercise capacity in patients with peripheral arterial occlusive disease. Thus, in this study, we tested the hypothesis that the expression of enhanced TRPV1 receptor and its responsiveness in primary afferent neurons innervating muscles initiate exaggerated reflex sympathetic responses after vascular insufficiency to the muscle. Muscle vascular insufficiency was induced by the femoral artery ligation in rats for 24 h. Our data show that 1) the ligation surgery leads to the upregulation of TRPV1 expression in the dorsal root ganglion; 2) the magnitude of the dorsal root ganglion neuron TRPV1 response induced by capsaicin is greater in vascular insufficiency (4.0 ± 0.31 nA, P < 0.05 vs. sham-operated control) than that in sham-operated control (2.9 ± 0.23 nA); and 3) renal sympathetic nerve activity and mean arterial pressure responses to capsaicin (0.5 μg/kg body wt) are also enhanced by vascular insufficiency (54 ± 11%, 9 ± 2 mmHg in sham-operated controls vs. 98 ± 13%, 33 ± 5 mmHg after vascular insufficiency, P < 0.05). In conclusion, sympathetic nerve responses to the activation of metabolite-sensitive TRPV1 receptors are augmented in rats with the femoral artery occlusion compared with sham-operated control animals, due to alterations in the expression of TRPV1 receptor and its responsiveness in sensory neurons.
Angiotensin converting enzyme-2 confers endothelial protection and attenuates atherosclerosis
Authors: Lovren Fina , Pan Yi , Quan Adrian , Teoh Hwee , Wang Guilin , Shukla Praphulla C. , Levitt Kevin S. , Oudit Gavin Y. , Al-Omran Mohammed , Stewart Duncan J. , Slutsky Arthur S. , Peterson Mark D. , Backx Peter H. , Penninger Josef M. , Verma Subodh
Published: July 2008

The endothelium plays a central role in the maintenance of vascular homeostasis. One of the main effectors of endothelial dysfunction is ANG II, and pharmacological approaches to limit ANG II bioactivity remain the cornerstone of cardiovascular therapeutics. Angiotensin converting enzyme-2 (ACE2) has been identified as a critical negative modulator of ANG II bioactivity, counterbalancing the effects of ACE in determining net tissue ANG II levels; however, the role of ACE2 in the vasculature remains unknown. In the present study, we hypothesized that ACE2 is a novel target to limit endothelial dysfunction and atherosclerosis. To this aim, we performed in vitro gain and loss of function experiments in endothelial cells and evaluated in vivo angiogenesis and atherosclerosis in apolipoprotein E-knockout mice treated with AdACE2. ACE2-deficient mice exhibited impaired endothelium-dependent relaxation. Overexpression of ACE2 in human endothelial cells stimulated endothelial cell migration and tube formation, and limited monocyte and cellular adhesion molecule expression; effects that were reversed in ACE2 gene silenced and endothelial cells isolated from ACE2-deficient animals. ACE2 attenuated ANG II-induced reactive oxygen species production in part through decreasing the expression of p22phox. The effects of ACE2 on endothelial activation were attenuated by pharmacological blockade of ANG-(1-7) with A779. ACE2 promoted capillary formation and neovessel maturation in vivo and reduced atherosclerosis in apolipoprotein E-knockout mice These data indicate that ACE2, in an ANG-(1-7)-dependent fashion, functions to improve endothelial homeostasis via a mechanism that may involve attenuation of NADPHox-induced reactive oxygen species production. ACE2-based treatment approaches may be a novel approach to limit aberrant vascular responses and atherothrombosis.
Mechanisms of conduction slowing during myocardial stretch by ventricular volume loading in the rabbit
Authors: Mills Robert W. , Narayan Sanjiv M. , McCulloch Andrew D.
Published: July 2008

Acute ventricular loading by volume inflation reversibly slows epicardial electrical conduction, but the underlying mechanism remains unclear. This study investigated the potential contributions of stretch-activated currents, alterations in resting membrane potential, or changes in intercellular resistance and membrane capacitance. Conduction velocity was assessed using optical mapping of isolated rabbit hearts at end-diastolic pressures of 0 and 30 mmHg. The addition of 50 μM Gd3+ (a stretch-activated channel blocker) to the perfusate had no effect on slowing. The effect of volume loading on conduction velocity was independent of changes in resting membrane potential created by altering the perfusate potassium concentration between 1.5 and 8 mM. Bidomain model analysis of optically recorded membrane potential responses to a unipolar stimulus suggested that the cross-fiber space constant and membrane capacitance both increased with loading (21%, P = 0.006, and 56%, P = 0.004, respectively), and these changes, when implemented in a resistively coupled one-dimensional network model, were consistent with the observed slowing (14%, P = 0.005). In conclusion, conduction slowing during ventricular volume loading is not attributable to stretch-activated currents or altered resting membrane potential, but a reduction of intercellular resistance with a concurrent increase of effective membrane capacitance results in a net slowing of conduction.
New insights into the atrial electrophysiology of rodents using a novel modality: the miniature-bipolar hook electrode
Authors: Etzion Yoram , Mor Michal , Shalev Aryeh , Dror Shani , Etzion Ohad , Dagan Amir , Beharier Ofer , Moran Arie , Katz Amos
Published: July 2008

Studies of atrial electrophysiology (EP) in rodents are challenging, and available data are sparse. Herein, we utilized a novel type of bipolar electrode to evaluate the atrial EP of rodents through small lateral thoracotomy. In anesthetized rats and mice, we attached two bipolar electrodes to the right atrium and a third to the right ventricle. This standard setup enabled high-resolution EP studies. Moreover, a permanent implantation procedure enabled EP studies in conscious freely moving rats. Atrial EP was evaluated in anesthetized rats, anesthetized mice (ICR and C57BL6 strains), and conscious rats. Signal resolution enabled atrial effective refractory period (AERP) measurements and first time evaluation of the failed 1:1 atrial capture, which was unexpectedly longer than the AERP recorded at near normal cycle length by 27.2 ± 2.3% in rats ( P < 0.0001; n = 35), 31.7 ± 8.3% in ICR mice ( P = 0.0001; n = 13), and 57.7 ± 13.7% in C57BL6 mice ( P = 0.015; n = 4). While AERP rate adaptation was noted when 10 S1s at near normal basic cycle lengths were followed by S2 at varying basic cycle length and S3 for AERP evaluation, such rate adaptation was absent using conventional S1S2 protocols. Atrial tachypacing in rats shortened the AERP values on a timescale of hours, but a reverse remodeling phase was noted thereafter. Comparison of left vs. right atrial pacing in rats was also feasible with the current technique, resulting in similar AERP values recorded in the low right atrium. In conclusion, our findings indicate that in vivo rate adaptation of the rodent atria is different than expected based on previous ex vivo recordings. In addition, atrial electrical remodeling of rats shows unique remodeling-reverse remodeling characteristics that are described here for the first time. Further understanding of these properties should help to determine the clinical relevance as well as limitations of atrial arrhythmia models in rodents.
Interaction between cardiac sympathetic afferent reflex and chemoreflex is mediated by the NTS AT1 receptors in heart failure
Authors: Wang Wei-Zhong , Gao Lie , Wang Han-Jun , Zucker Irving H. , Wang Wei
Published: July 2008

Several sympathoexcitatory reflexes, such as the cardiac sympathetic afferent reflex (CSAR) and arterial chemoreflex, are significantly augmented and contribute to elevated sympathetic outflow in chronic heart failure (CHF). This study was undertaken to investigate the interaction between the CSAR and the chemoreflex in CHF and to further identify the involvement of angiotensin II type 1 receptors (AT1Rs) in the nucleus of the tractus solitarius (NTS) in this interaction. CHF was induced in rats by coronary ligation. Acute experiments were performed in anesthetized rats. The chemoreflex-induced increase in cardiovascular responses was significantly greater in CHF than in sham-operated rats after either chemical or electrical activation of the CSAR. The inhibition of the CSAR by epicardial lidocaine reduced the chemoreflex-induced effects in CHF rats but not in sham-operated rats. Bilateral NTS injection of the AT1R antagonist losartan (10 and 100 pmol) dose-dependently decreased basal sympathetic nerve activity in CHF but not in sham-operated rats. This procedure also abolished the CSAR-induced enhancement of the chemoreflex. The discharge and chemosensitivity of NTS chemosensitive neurons were significantly increased following the stimulation of the CSAR in sham-operated and CHF rats, whereas CSAR inhibition by epicardial lidocaine significantly attenuated chemosensitivity of NTS neurons in CHF but not in sham-operated rats. Finally, the protein expression of AT1R in the NTS was significantly higher in CHF than in sham-operated rats. These results demonstrate that the enhanced cardiac sympathetic afferent input contributes to an excitatory effect of chemoreflex function in CHF, which is mediated by an NTS-AT1R-dependent mechanism.
A comparison of reactive oxygen species metabolism in the rat aorta and vena cava: focus on xanthine oxidase
Authors: Szasz Theodora , Thompson Janice M. , Watts Stephanie W.
Published: July 2008

Reactive oxygen species (ROS) are important mediators in vascular biology. Venous function, although relevant to cardiovascular disease, is still understudied. We compared aspects of ROS metabolism between a major artery (the aorta) and a major vein (the vena cava, VC) of the rat, with the hypothesis that venous ROS metabolism would be overall increased compared with its arterial counterpart. Superoxide and hydrogen peroxide (H2O2) release in basal conditions was higher in VC compared with aorta. The antioxidant capacity for H2O2was also higher in VC than in aorta. Exogenous superoxide induced a higher contraction in VC compared with aorta. Protein expression of three major ROS metabolizing enzymes, xanthine oxidase (XO), CuZn-SOD, and catalase, was higher in VC compared with aorta. Because XO seemed a likely source of the higher VC ROS levels, we examined it further and found higher mRNA expression and activity of XO in VC compared with aorta. We also investigated the impact of XO inhibition by allopurinol on aorta and VC functional responses to norepinephrine, ANG II, ET-1, and ACh. Maximal ET-1-mediated contraction was decreased by allopurinol in VC but not in the aorta. Our results suggest that there are overall differences in ROS metabolism between aorta and VC, with the latter operating normally at a higher set point, releasing but also being able to handle, higher ROS levels. We propose XO to be an important source for these differences. The result of this particular comparison may be reflective of a general arteriovenous contrast.
Exogenous zinc protects cardiac cells from reperfusion injury by targeting mitochondrial permeability transition pore through inactivation of glycogen synthase kinase-3β
Authors: Chanoit Guillaume , Lee SungRyul , Xi Jinkun , Zhu Min , McIntosh Rachel A. , Mueller Robert A. , Norfleet Edward A. , Xu Zhelong
Published: July 2008

The purpose of this study was to determine whether exogenous zinc prevents cardiac reperfusion injury by targeting the mitochondrial permeability transition pore (mPTP) via glycogen synthase kinase-3β (GSK-3β). The treatment of cardiac H9c2 cells with ZnCl2 (10 μM) in the presence of zinc ionophore pyrithione for 20 min significantly enhanced GSK-3β phosphorylation at Ser9, indicating that exogenous zinc can inactivate GSK-3β in H9c2 cells. The effect of zinc on GSK-3β activity was blocked by the phosphatidylinositol 3-kinase (PI3K) inhibitor LY-294002 but not by the mammalian target of rapamycin (mTOR) inhibitor rapamycin or the PKC inhibitor chelerythrine, implying that PI3K but not mTOR or PKC accounts for the action of zinc. In support of this interpretation, zinc induced a significant increase in Akt but not mTOR phosphorylation. Further experiments found that zinc also increased mitochondrial GSK-3β phosphorylation. This may indicate an involvement of the mitochondria in the action of zinc. The effect of zinc on mitochondrial GSK-3β phosphorylation was not altered by the mitochondrial ATP-sensitive K+ channel blocker 5-hydroxydecanoic acid. Zinc applied at reperfusion reduced cell death in cells subjected to simulated ischemia/reperfusion, indicating that zinc can prevent reperfusion injury. However, zinc was not able to exert protection in cells transfected with the constitutively active GSK-3β (GSK-3β-S9A-HA) mutant, suggesting that zinc prevents reperfusion injury by inactivating GSK-3β. Cells transfected with the catalytically inactive GSK-3β (GSK-3β-KM-HA) also revealed a significant decrease in cell death, strongly supporting the essential role of GSK-3β inactivation in cardioprotection. Moreover, zinc prevented oxidant-induced mPTP opening through the inhibition of GSK-3β. Taken together, these data suggest that zinc prevents reperfusion injury by modulating the mPTP opening through the inactivation of GSK-3β. The PI3K/Akt signaling pathway is responsible for the inactivation of GSK-3β by zinc.
MAPK signaling pathways are needed for survival of H9c2 cardiac myoblasts under extracellular alkalosis
Authors: Stathopoulou Konstantina , Beis Isidoros , Gaitanaki Catherine
Published: July 2008

pH is one of the most important physiological parameters, with its changes affecting the function of vital organs like the heart. However, the effects of alkalosis on the regulation of cardiac myocyte function have not been extensively investigated. Therefore, we decided to study whether the mitogen-activated protein kinase (MAPK) signaling pathways [c-Jun NH2-terminal kinases (JNKs), extracellular signal-regulated kinases (ERKs), and p38 MAPK] are activated by alkalosis induced with Tris-Tyrode buffer at two pH values, 8.5 and 9.5, in H9c2 rat cardiac myoblasts. These buffers also induced intracellular alkalinization comparable to that induced by 1 mM NH4Cl. The three MAPKs examined presented differential phosphorylation patterns that depended on the severity and the duration of the stimulus. Inhibition of Na+/H+ exchanger (NHE)1 by its inhibitor HOE-642 prevented alkalinization and partially attenuated the alkalosis (pH 8.5)-induced activation of these kinases. The same stimulus also promoted c-Jun phosphorylation and enhanced the binding at oligonucleotides bearing the activator protein-1 (AP-1) consensus sequence, all in a JNK-dependent manner. Additionally, mitogen- and stress-activated kinase 1 (MSK1) was transiently phosphorylated by alkalosis (pH 8.5), and this was abolished by the selective inhibitors of either p38 MAPK or ERK pathways. JNKs also mediated Bcl-2 phosphorylation in response to incubation with the alkaline medium (pH 8.5), while selective inhibitors of the three MAPKs diminished cell viability under these conditions. All these data suggest that alkalosis activates MAPKs in H9c2 cells and these kinases, in turn, modify proteins that regulate gene transcription and cell survival.
Roles of cell and microvillus deformation and receptor-ligand binding kinetics in cell rolling
Authors: Pawar Parag , Jadhav Sameer , Eggleton Charles D. , Konstantopoulos Konstantinos
Published: July 2008

Polymorphonuclear leukocyte (PMN) recruitment to sites of inflammation is initiated by selectin-mediated PMN tethering and rolling on activated endothelium under flow. Cell rolling is modulated by bulk cell deformation (mesoscale), microvillus deformability (microscale), and receptor-ligand binding kinetics (nanoscale). Selectin-ligand bonds exhibit a catch-slip bond behavior, and their dissociation is governed not only by the force but also by the force history. Whereas previous theoretical models have studied the significance of these three “length scales” in isolation, how their interplay affects cell rolling has yet to be resolved. We therefore developed a three-dimensional computational model that integrates the aforementioned length scales to delineate their relative contributions to PMN rolling. Our simulations predict that the catch-slip bond behavior and to a lesser extent bulk cell deformation are responsible for the shear threshold phenomenon. Cells bearing deformable rather than rigid microvilli roll slower only at high P-selectin site densities and elevated levels of shear (≥400 s−1). The more compliant cells (membrance stiffness = 1.2 dyn/cm) rolled slower than cells with a membrane stiffness of 3.0 dyn/cm at shear rates >50 s−1. In summary, our model demonstrates that cell rolling over a ligand-coated surface is a highly coordinated process characterized by a complex interplay between forces acting on three distinct length scales.
Endothelial cell barrier protection by simvastatin: GTPase regulation and NADPH oxidase inhibition
Authors: Chen Weiguo , Pendyala Srikanth , Natarajan Viswanathan , Garcia Joe G. N. , Jacobson Jeffrey R.
Published: July 2008

The statins, hydroxy-3-methylglutaryl-CoA reductase inhibitors that lower serum cholesterol, exhibit myriad clinical benefits, including enhanced vascular integrity. One potential mechanism underlying increased endothelial cell (EC) barrier function is inhibition of geranylgeranylation, a covalent modification enabling translocation of the small GTPases Rho and Rac to the cell membrane. While RhoA inhibition attenuates actin stress fiber formation and promotes EC barrier function, Rac1 inhibition at the cell membrane potentially prevents activation of NADPH oxidase and subsequent generation of superoxides known to induce barrier disruption. We examined the relative regulatory effects of simvastatin on RhoA, Rac1, and NADPH oxidase activities in the context of human pulmonary artery EC barrier protection. Confluent EC treated with simvastatin demonstrated significantly decreased thrombin-induced FITC-dextran permeability, a reflection of vascular integrity, which was linked temporally to simvastatin-mediated actin cytoskeletal rearrangement. Compared with Rho inhibition alone (Y-27632), simvastatin afforded additional protection against thrombin-mediated barrier dysfunction and attenuated LPS-induced EC permeability and superoxide generation. Statin-mediated inhibition of both Rac translocation to the cell membrane and superoxide production were attenuated by geranylgeranyl pyrophosphate (GGPP), indicating that these effects are due to geranylgeranylation inhibition. Finally, thrombin-induced EC permeability was modestly attenuated by reduced Rac1 expression (small interfering RNA), whereas these effects were made more pronounced by simvastatin pretreatment. Together, these data suggest EC barrier protection by simvastatin is due to dual inhibitory effects on RhoA and Rac1 as well as the attenuation of superoxide generation by EC NADPH oxidase and contribute to the molecular mechanistic understanding of the modulation of EC barrier properties by simvastatin.
Role of matrix metalloprotease-9 in hyperoxic injury in developing lung
Authors: Chetty Anne , Cao Gong-Jie , Severgnini Mariano , Simon Amy , Warburton Rod , Nielsen Heber C.
Published: July 2008

Matrix metalloprotease-9 (MMP-9) is increased in lung injury following hyperoxia exposure in neonatal mice, in association with impaired alveolar development. We studied the role of MMP-9 in the mechanism of hyperoxia-induced functional and histological changes in neonatal mouse lung. Reduced alveolarization with remodeling of ECM is a major morbidity component of oxidant injury in developing lung. MMP-9 mediates oxidant injury in developing lung causing altered lung remodeling. Five-day-old neonatal wild-type (WT) and MMP-9 (−/−) mice were exposed to hyperoxia for 8 days. The lungs were inflation fixed, and sections were examined for morphometry. The mean linear intercept and alveolar counts were evaluated. Immunohistochemistry for MMP-9 and elastin was performed. MMP-2, MMP-9, type I collagen, and tropoelastin were measured by Western blot analysis. Lung quasistatic compliance was studied in anaesthetized mice. MMP-2 and MMP-9 were significantly increased in lungs of WT mice exposed to hyperoxia compared with controls. Immunohistochemistry showed an increase in MMP-9 in mesenchyme and alveolar epithelium of hyperoxic lungs. The lungs of hyperoxia-exposed WT mice had less gas exchange surface area and were less compliant compared with room air-exposed WT and hyperoxia-exposed MMP-9 (−/−) mice. Type I collagen and tropoelastin were increased in hyperoxia-exposed WT with aberrant elastin staining. These changes were ameliorated in hyperoxia-exposed MMP-9 (−/−) mice. MMP-9 plays an important role in the structural changes consequent to oxygen-induced lung injury. Blocking MMP-9 activity may lead to novel therapeutic approaches in preventing bronchopulmonary dysplasia.