Ring Tension Research Articles

Two Isoforms of Myosin-II Account for the Tension of the Fission Yeast Cytokinetic Ring

During cytokinesis, an actomyosin contractile ring constricts and drives or regulates division of the cell into two. Tension production is thought to be the principal function of the cytokinetic ring, but measurements of this fundamental property have not been available. Myosin-II is thought to generate tension, but a requirement was not demonstrated.Here, we developed a method to measure ring tension in fission yeast protoplasts, cells that lack cell wall in which furrowing by the contractile ring is supported by plasma membrane tension alone as demonstrated by the almost perfectly spherical lobes flanking the furrow. We use a force balance at the furrow to deduce the ring tension, after measuring the membrane tension using micropipette aspiration and accurately measuring the furrow geometry.Applying the technique to wild type and myosin-II mutant cells, we show for the first time that myosin-II is required for normal tension, and we measured the contributions of the two myosin-II isoforms present in the fission yeast ring, Myo2 and Myp2. As rings constricted, the tension increased from ∼400 to ∼800 pN. Tension was lowered by the myosin-II inhibitor blebbistatin, and tension in cells with mutations in Myo2p or Myp2p showed that the two isoforms account for all of the tension, with contributions of ∼ 65% and ∼ 40%, respectively.A molecularly detailed 3D simulation of the ring, together with the experimental tension measurements, suggest that tension is generated solely by the pulling of myosin-II on actin filaments anchored at their barbed ends to the plasma membrane. The simulations reproduced experiment, including the steady increase of ring tension as rings constricted, with best fit forces per myosin head of ∼ 1 pN for both isoforms, similar to muscle myosin II.

Roles of different mitochondrial electron transport chain complexes in hypoxia-induced pulmonary vasoconstriction.

This study was designed to investigate the roles of different mitochondrial electron transport chain (ETC) complexes (I, II, III, and IV) on hypoxia-induced hypoxic pulmonary vasoconstriction (HPV). The third and fourth pulmonary arteries were collected from the normal tissues adjacent to tumors in 16 patients with lung cancer who had undergone lung cancer resections to isolate pulmonary artery smooth muscle cells (PASMCs). PASMCs were divided into seven groups and exposed to one of the following treatments: (1) normoxia (21% O(2), 5% CO(2), and 74% N(2)); (2) hypoxia (1% O(2), 5% CO(2), 94% N(2)); (3) hypoxia plus ETC complex I inhibitor MPP; (4) hypoxia plus ETC complex II inhibitor TTFA; (5) hypoxia plus ETC complex III Q(o) (pre) site inhibitor myxothiazol; (6) hypoxia plus ETC complex III Qi (post) site inhibitor antimycin A; (7) hypoxia plus ETC complex IV inhibitor NaN(3). Intracellular [Ca(2+) ]i and [ROS]i, mitochondrial [ROS]i, and PA rings tension were measured. Intracellular [Ca(2+) ]i and [ROS]i, mitochondrial [ROS]i, and PA ring tension were increased after hypoxia for 10 min. Mitochondrial ETC complex inhibitor MPP, TTFA, and myxothiazol significantly reduced [Ca(2+) ]i [ROS]i and PA tension (P < 0.01), whereas antimycin A and NaN(3) did not effectively reduce them. These results demonstrated it were mitochondrial ETC complex I, II, and III Q(o) site but not III Q(i) site and complex IV contribute to hypoxic pulmonary vasoconstriction and pulmonary hypertension.

Comparison of early and delayed transplantation of adipose tissue-derived mesenchymal stem cells on pulmonary arterial function in monocrotaline-induced pulmonary arterial hypertensive rats

The aim of this article was to investigate the effects of early and delayed transplantation of adipose tissue-derived mesenchymal stem cells (ADMSCs) on pulmonary vasomotion in monocrotaline (MCT)-induced pulmonary arterial hypertensive (PAH) rats. Adipose tissue-derived mesenchymal stem cells were isolated from inguinal subcutaneous adipose tissue of Sprague-Dawley (SD) rats. Eighty male SD rats were divided into four groups ( n = 20 per group): normal control (Ctr), PAH, early (at day 7, ADMSCs-7), and delayed (at day 14, ADMSCs-14) ADMSC intervention. PAH was induced by a single dose intraperitoneal injection of 40 mg/kg MCT. About 1 × 106 ADMSCs were delivered via left external jugular vein. Mean pulmonary arterial pressure (MPAP) was measured by catheterization at days 21 and 28 after MCT injection. Pulmonary arteriolar endothelium-dependent relaxation (EDdR), endothelium-independent relaxation (EDiR), and vasoconstriction function were evaluated by the physiological vascular ring tension recording system. Mean pulmonary arterial pressure (mmHg) was increased on days 21 (26.88 ± 0.86 vs. 14.88 ± 0.98, P < 0.05) and 28 (32.22 ± 0.71 vs. 15.16 ± 0.95, P < 0.05) after MCT administration; EDdR and EDiR were lower in PAH rats at the 21st day (pD2:EDdR: 4.85 ± 0.29 vs. 8.12 ± 0.48 and EDiR: 6.28 ± 0.38 vs. 8.64 ± 0.35; all P < 0.05) and 28th day (pD2:EDdR: 3.22 ± 0.61 vs. 7.93 ± 0.5 and pD2:EDiR: 5.4 ± 0.55 vs. 8.58 ± 0.41; all P < 0.05). Mean pulmonary arterial pressure in ADMSCs-7 was decreased on the 21st day (16.37 ± 0.94 vs. 26.88 ± 0.86 mmHg, P < 0.05) and 28th day (18.26 ± 1.41 vs. 32.22 ± 0.71 mmHg, P < 0.05). Similarly, MPAP in ADMSC-14 was also lowered on days 21 and 28. EDdR in ADMSCs-7 was increased on day 21 (pD2: 7.48 ± 0.31 vs. 4.85 ± 0.29, P < 0.05) and day 28 (6.29 ± 0.52 vs. 3.22 ± 0.61, P < 0.05). EDdR in ADMSCs-14 was also increased on day 21 (pD2: 8.08 ± 0.37 vs. 4.85 ± 0.29, P < 0.05) and day 28 (6.21 ± 0.67 vs. 3.22 ± 0.61, P < 0.05). EDiR in both ADMSCs-7 and ADMSCs-14 was increased on days 21 and 28. There was no significant difference in EDdR and EDiR between ADMSCs-EI and ADMSCs-DI. The impairment of EDdR and EdiR in PA was ameliorated, and PAH was reduced by both early and delayed transplantation of ADMSCs.

ChemInform Abstract: Cellular Uptake: Lessons from Supramolecular Organic Chemistry

AbstractReview: 78 refs.+ subrefs.

Modeling Epoxidation of Drug-like Molecules with a Deep Machine Learning Network.

Drug toxicity is frequently caused by electrophilic reactive metabolites that covalently bind to proteins. Epoxides comprise a large class of three-membered cyclic ethers. These molecules are electrophilic and typically highly reactive due to ring tension and polarized carbon–oxygen bonds. Epoxides are metabolites often formed by cytochromes P450 acting on aromatic or double bonds. The specific location on a molecule that undergoes epoxidation is its site of epoxidation (SOE). Identifying a molecule’s SOE can aid in interpreting adverse events related to reactive metabolites and direct modification to prevent epoxidation for safer drugs. This study utilized a database of 702 epoxidation reactions to build a model that accurately predicted sites of epoxidation. The foundation for this model was an algorithm originally designed to model sites of cytochromes P450 metabolism (called XenoSite) that was recently applied to model the intrinsic reactivity of diverse molecules with glutathione. This modeling algorithm systematically and quantitatively summarizes the knowledge from hundreds of epoxidation reactions with a deep convolution network. This network makes predictions at both an atom and molecule level. The final epoxidation model constructed with this approach identified SOEs with 94.9% area under the curve (AUC) performance and separated epoxidized and non-epoxidized molecules with 79.3% AUC. Moreover, within epoxidized molecules, the model separated aromatic or double bond SOEs from all other aromatic or double bonds with AUCs of 92.5% and 95.1%, respectively. Finally, the model separated SOEs from sites of sp2 hydroxylation with 83.2% AUC. Our model is the first of its kind and may be useful for the development of safer drugs. The epoxidation model is available at http://swami.wustl.edu/xenosite.

Enhanced store-operated Ca2+ entry and canonical transient receptor potential expression in new rat model of pulmonary hypertension

Objective To investigate the role of canonical transient receptor potential 1 (TRPC1)in pneumonectomy(PE) plus subcutaneous injection of monocrotaline(MCT)- induced pulmonary artery hypertension(PH)in rats. Methods SD rats underwent unilateral lobectomy, and 1 week later, rats were intraperitoneally injected with 2% MCT(50 mg/kg).After 3 weeks, mean right ventricular pressure(m RVP) and right ventricular mass index(RVMI) were measured. The lung sections were stained by hematoxylin and eosin(HE)and observed under light microscope.Real - time reverse transcriptase- polymerase chain reaction(RT- qPCR) was performed to detect TRPC1 m RNA expression in rat pulmonary arteries(PAs).Store- operated calcium channel(SOCC) agonist cyclopiazonic acid(CPA)- induced PAs contraction was measured by vascular ring tension analysis and the intracellular Ca2+ concentration([Ca2+]i)of pulmonary artery smooth muscle cells (PASMCs) was monitored by Fluo3- AM assay.Meanwhile the effect of endothelin- 1(ET- 1)-induced vasocontration, and the relaxation of gadolinium(Gd3+) on ET- 1- induced PAs contraction was measured. Results In comparison to the control group, rats developed severe PAH, and right ventricular hypertrophy in PE+ MCT group.The expression of TRPC1 m RNA in control group was more than 3 folds of that in PE+ MCT group.CPA- induced vasoconstriction was increased from(16.6±1.5)% in control group to(126.6±15.4)% in PE+ MCT group(n= 8,P< 0.01), and Ca2+ influx in PASMCs evoked by CPA was enhanced from(268±76) nmol/L in control group to(1 832±867) nmol/L in PE+ MCT group(n= 8,P< 0.01).Gd3+- induced relaxation to Endothelin- 1 vasoconstriction was also potentiated from(36.9±3.7)% in control group to(70.1± 2.6)% in PE+ MCT group(n= 8,P< 0.05) Conclusion PE+ MCT- induced PH is associated with increased TRPC1 expression and TRPC/SOCC- induced store operated Ca2+ entry. Key words: Ca2+; Pneumonectomy; Monocrotaline

Ring Tension Applied to Thiol‐Mediated Cellular Uptake

AbstractThe objective of the study was to explore the potential of ring tension in cyclic disulfides for thiol‐mediated cellular uptake. Fluorescent probes that cannot enter cells were equipped with cyclic disulfides of gradually increasing ring tension. As demonstrated by flow cytometry experiments, uptake into HeLa Kyoto cells increased with increasing tension. Differences in carbon‐sulfur‐sulfur‐carbon (CSSC) dihedral angles as small as 8° caused significant changes in uptake efficiency. Uptake with high ring tension was better than with inactivated or activated linear disulfides or with thiols. Conversion of thiols on the cell surface into sulfides and disulfides decreased the uptake. Reduction of exofacial disulfides into thiols increased the uptake of transporters with disulfides and inactivated controls with thiols. These results confirm the occurrence of dynamic covalent disulfide‐exchange chemistry on cell surfaces. Mechanistic and colocalization studies indicate that endocytosis does not fully account for this cellular uptake with ring tension.

Ring Tension Applied to Thiol-Mediated Cellular Uptake.

The objective of the study was to explore the potential of ring tension in cyclic disulfides for thiol-mediated cellular uptake. Fluorescent probes that cannot enter cells were equipped with cyclic disulfides of gradually increasing ring tension. As demonstrated by flow cytometry experiments, uptake into HeLa Kyoto cells increased with increasing tension. Differences in carbon-sulfur-sulfur-carbon (CSSC) dihedral angles as small as 8° caused significant changes in uptake efficiency. Uptake with high ring tension was better than with inactivated or activated linear disulfides or with thiols. Conversion of thiols on the cell surface into sulfides and disulfides decreased the uptake. Reduction of exofacial disulfides into thiols increased the uptake of transporters with disulfides and inactivated controls with thiols. These results confirm the occurrence of dynamic covalent disulfide-exchange chemistry on cell surfaces. Mechanistic and colocalization studies indicate that endocytosis does not fully account for this cellular uptake with ring tension.

Double Compression Expansion Engine Concepts: A Path to High Efficiency

Internal combustion engine (ICE) fuel efficiency is a balance between good indicated efficiency and mechanical efficiency. High indicated efficiency is reached with a very diluted air/fuel-mixture and high load resulting in high peak cylinder pressure (PCP). On the other hand, high mechanical efficiency is obtained with very low peak cylinder pressure as the piston rings and bearings can be made with less friction. This paper presents studies of a combustion engine which consists of a two stage compression and expansion cycle. By splitting the engine into two different cycles, high-pressure (HP) and low-pressure (LP) cycles respectively, it is possible to reach high levels of both indicated and mechanical efficiency simultaneously. The HP cycle is designed similar to today's turbo-charged diesel engine but with an even higher boost pressure, resulting in high PCP. To cope with high PCP, the engine needs to be rigid. The usage of higher piston ring tension and larger bearings are examples of measures to cope with higher PCP. These measures will cost in terms of friction. Hence, mechanical efficiency is not as good as other engine concepts with lower PCP. The low-pressure cycle on the other hand, uses a design more similar to current naturally aspirated (NA) spark ignited (SI) engines, but designed for even lower PCP. Because of this, the engine does not need to be as rigidly designed and the overall friction levels will be much lower. By combining these two engine philosophies, a total engine concept with both high indicated and mechanical efficiencies can be achieved. Simulations show net indicated efficiency above 60% and a brake efficiency of 56%. (Less)

Levels of autoantibodies against AT1-receptor in hypertensive patients with acute coronary syndromes and its role in coronary artery vasoconstriction

To explore the levels of autoantibodies against AT1-receptor (AT1-AA) in hypertensive patients with acute coronary syndrome (ACS) and observe the in vitro effects of AT1-AA on resting tension of isolated anterior descending artery of vascular ring in male Wistar rats. All patients were recruited from June 2007 to August 2008. There were hypertensive patients with ACS (n = 120), those with simple hypertension (n = 253) and those with simple ACS (n = 115). And the outpatients for health examination during the same period were selected as healthy control group (n = 188). The second extracellular loop amino acid sequences of peptides of ATI receptor was synthesized and used as antigen (AT1-Ag) and sialic acid-enzyme-linked immunosorbent assay (SA-ELISA) for detect the serum levels of AT1-AA. Microvascular ring tension technology was used to test the vascular loop resting tension of anterior descending coronary artery from rats induced by a high-fat diet. The positive rates of AT1-AA in patients with simple hypertension (35.2%) and those with simple ACS (30.4%) were significantly higher than those in healthy control group (7.2%, P < 0.01). And the positive rate of AT1-AA in hypertensive patients with ACS (43.3%) was significantly higher than that in those with simple hypertension (35.2%, P < 0.05) and that in healthy control group (7.2%, P < 0.05).Furthermore, AT1-AA increased the vascular loop resting tension of anterior descending coronary artery rings in rats induced by a high-fat diet in a dose-dependant manner. And the vasoconstrictive action of AT1-AA was equal to 46.4% of AngII's action. And such an action was blocked by losartan and antigens. The level of AT1-AA increases markedly in hypertensive patients with ACS. And AT1-AA induces vasoconstrictive effects on anterior descending artery rings in rats induced by a high-fat diet.

Vasodilative effect and the underlying mechanism of gingerol on isolated thoracic aorta ring of rabbits

Objective To observe the effect of gingerol on the isolated thoracic aorta ring of rabbits and investigate its underlying mechanisms. Methods The thoracic aortic ring muscle strips with intact and denuded endothelium were prepared and placed in an organ chamber containing physiological salt solution(PSS).Every strip was connected to the tension transducer and the change of the vascular ring tension was recorded and analyzed by the biological signal collection and analysis computer system.Th isotonic tension of thoracic aortic rings with intact and denuded endothelium precontracted by norepinephrine(NE,1×10-5 mol/L)or KCl(20 mmol/L)was recorded before and after administrating gingerol.Meanwhile, we also observed the effects of N-nitro-L-arginine methyl ester(L-NAME,1×10-4 mol/L)and indomethacin(1×10-8 mol/L)on the action of gingerol in the rings. Results (1) Administration of 1×10-5 mol/L NE or 20 mmol/L KCl could produce the contraction effect in the thoracic aortic rings with intact endothelium.gingerol induced the muscle relaxation of aorta in both intact and denuded endothelium groups in a dose-dependant manner, meanwhile, the relaxation effect of gingerol was stronger in intact endothelium group than that in denuded endothelium group(P<0.05).(2)L-NAME could inhibit the vasodilative role caused by gingerol in intact endothelium group(%,94.83±3.63 vs.96.83±1.82, 91.17±2.89 vs.94.83±2.68, 83.83±2.23 vs.94.67±2.7, 78.00±3.54 vs.92.33±2.91,67.83±2.37 vs.90.83±3.77, 62.83±3.42 vs.89.67±3.15 respectively in NE-treated group and 90.33±8.33 vs.98.17±7.56,80.83±7.24 vs.96.83±7.28,70.83±7.57 vs.92.17 ±7.31,67.83±7.68 vs.89.83±7.23,62.83±7.49 vs.90.33±8.87,57.33±8.32 vs.87.67±8.97 respectively in KCl-treated group, P<0.05).(3)Indomethacin could inhibit the vasodilative role caused by gingerol in intact endothelium group(%,93.83±7.61 vs.97.83±7.45,92.50±10.13 vs.95.33±8.36,86.67 ±8.24 vs.93.83±7.28, 79.83±7.36 vs.89.83±7.63, 67.83±7.46 vs.85.33±8.94, 61.83±7.55 vs. 81.83±7.25 respectively in NE-treated group and 90.17±7.77 vs.96.17±7.31,79.67±8.65 vs.91.33± 8.62,72.17±7.48 vs.85.67±8.76,70.83±7.78 vs.83.17±7.79,56.83±7.62 vs.77.83±7.29,54.17± 7.68 vs.74.83±7.34 respectively in KCl-treated group, P< 0.05). Conclusion (1)Gingero preferentially antagonized the contraction effect induced by NE or KCl in a dose-dependent manner.(2)The vasorelaxation effect of gingerol on the thoracic aortic ring muscle strips was relevant to the production of NO and prostacyclin. Key words: Gingerol; Thoracic aorta; Endothelium; Nitric oxide; Prostacyclin

Measurements and Simulations of the Fission Yeast Cytokinetic Ring Tension during Constriction

Cytokinesis in animals and fungi requires the assembly and constriction of an actomyosin contractile ring at the site of cell division. However, the ring tension_the ring's principal mechanical property_has rarely been measured. Consequently, it has not been possible to relate the organization of the ring to its principal function. To address this, we recently developed a method to measure the cytokinetic ring tension in fission yeast for the first time (Stachowiak et al., Dev. Cell, 2014). We used micropipette aspiration on yeast protoplasts (whose cell walls have been enzymatically digested) to measure the membrane tension and imaged the geometry of the membrane furrow induced by the tense ring by fluorescence microscopy in order to deduce the ring tension from a force balance at the furrow. The availability of a method to measure cytokinetic ring tension has opened the door to observing the effect of mutations and drug treatments on ring tension that were previously invisible. Here, we develop the ring tension measurement to track ring tension in real time throughout the full course of constriction, and we measured tension in fission yeast mutants and wild type cells following drug treatments where the activity and dynamics of myosin or actin are compromised. We coordinated these measurements with a mathematical model of the constricting ring to test the mechanism of tension production and constriction. Insights into this mechanism that have resulted highlight the sensitivity to actin filament length and polymerization and the role of myosin activity in maintenance of steady state tension.

The fission yeast cytokinetic contractile ring regulates septum shape and closure.

During cytokinesis, fission yeast and other fungi and bacteria grow a septum that divides the cell in two. In fission yeast closure of the circular septum hole by the β-glucan synthases (Bgs) and other glucan synthases in the plasma membrane is tightly coupled to constriction of an actomyosin contractile ring attached to the membrane. It is unknown how septum growth is coordinated over scales of several microns to maintain septum circularity. Here, we documented the shapes of ingrowing septum edges by measuring the roughness of the edges, a measure of the deviation from circularity. The roughness was small, with spatial correlations indicative of spatially coordinated growth. We hypothesized that Bgs-mediated septum growth is mechanosensitive and coupled to contractile ring tension. A mathematical model showed that ring tension then generates almost circular septum edges by adjusting growth rates in a curvature-dependent fashion. The model reproduced experimental roughness statistics and showed that septum synthesis sets the mean closure rate. Our results suggest that the fission yeast cytokinetic ring tension does not set the constriction rate but regulates septum closure by suppressing roughness produced by inherently stochastic molecular growth processes.

Coarse-Grained Simulations Reveal Mechanisms of Fission Yeast Cytokinesis

Cytokinesis in fission yeast requires the presence of the actomyosin ring that constricts the membrane to divide the cell. Despite lots of effort, the molecular mechanism by which the ring tension is created remains poorly understood. This is largely due to the lack of structural details of of the ring, e.g., how actin filaments (F-actin) are arranged and what myosin conformations exist. As several models exist we decided to develop a computational approach to test whether these models are biophysically reasonable when simulated. Starting with a very simple model in which only actin filaments and bipolar myosin molecules are present we showed that myosin could slide F-actin but contraction did not occur. Addition of actin crosslinkers then helped contract the ring which in turn could pull down a coarse-grained membrane added to the system later. By tuning parameters and properties of the ring's components to match with data from electron cryotomography, we showed that coarse-grained simulations could help reveal the mechanism for the ring constriction.

Ring-opening polymerization of rac-lactide using anilinotropone-based aluminum complexes-sidearm effect on the catalysis

A series of anilinotropone-based aluminum complexes of general formula (Ar-NC7H5O)AlMe2 (1, Ar = Ph; 2, Ar = 2,6-iPrC6H3; 3, Ar = (2-O-Ph)C6H4; 4, Ar = (2-O-2,6-iPr2-Ph)C6H4; 5, Ar = (2-S-Ph)C6H4) were synthesized at high yields. These complexes were characterized by 1H, 13C NMR spectroscopy, elemental analysis and mass spectroscopy. X-ray analysis of complexes 1, 3 and 5 showed that they exist as dimeric species in solid state and the Al center adopts a distorted trigonal-bipyramidal geometry. Complexes 1–5 are highly active in the ring-opening polymerization (ROP) of rac-lactide (rac-LA) in the presence of benzyl alcohol as an initiator. Sidearm on the ligand has a dramatic effect on the catalysis, and complexes 3–5 bearing heteroatom containing sidearm are much more active than complexes 1 and 2. Especially, near complete consumption of the monomer was observed for complex 3 at rac-LA/Al ratio of 100 and 80 °C, representing one of the most active aluminum catalysts for ROP of rac-LA. The smaller aluminum chelate ring size and the resulting bigger ring tension may contribute to the high activity. In addition to the catalytic activity, the isotacticity of the resulting polylactide is also affected by the sidearm.

A Practical Approach to Evaluate Stress–Strain Behavior of Remotely Handled Pressure Tubes of Nuclear Reactors Using Ring Tension Test

Determination of transverse mechanical properties of nuclear reactor pressure tubes is important to perform integrity assessment of these components, especially for those which have been subjected to extended duration of reactor operation. Machining of standard tensile specimens is difficult in case the specimens are to be obtained from these thin tubular components. However, the more practicable option would be to fabricate the ring tensile type of specimens by directly machining them from the tube as it is a less cumbersome option in comparison to that of machining of the miniature plate tensile specimens especially when the component has been discharged from the nuclear reactor and are to be handled remotely due to activity. But, adopting this approach requires certain specific standardization work to be done to make the technique fully acceptable, adaptable and reliable when compared to the conventional techniques. In this work, we have developed a practical approach to evaluate the transverse mechanical properties and the stress–strain behavior of tubular components using ring tensile test. Different types of mandrel design and gauge length orientations of the specimens with respect to loading axis have been explored and the dependence of the results on the above parameters has been discussed. Two different types of Zirconium based alloys as used in Indian nuclear reactors have been tested with this technique and the material stress–strain behavior have been evaluated. Finally, the advantages of this method to evaluate the transverse mechanical properties of remotely-operated tubular components have been highlighted and use of appropriate loading and mandrel geometry for the ring tensile test have been recommended. The paper elucidates the methodology followed in validating the ring tensile test results in order to make the test suitable for the estimation of the irradiation-induced alteration in mechanical properties of nuclear reactor pressure tubes.

Development of the indirect ring tension fracture test for hot-mix asphalt

Almost all of the current hot-mix asphalt (HMA) fracture tests are considered to be research tools. This paper describes the development of the indirect ring tension (IRT) fracture test for HMA, which was designed to be an effective and user-friendly test that could be used at the Department of Transportation level. Numerical modelling was utilised to calibrate the stress intensity factor formula of the IRT fracture test for various specimen dimensions. The results of this extensive analysis were encapsulated in a single equation. An experimental plan was developed to optimise the test parameters for HMA specimens. The experiment results revealed that the test is highly repeatable, and capable of capturing the variations in the fracture properties of HMA. Moreover, the data from laboratory tests were utilised to estimate the maximum allowable crack lengths for the pavements based on a viscoelastic model.

Mechanism of Cytokinetic Contractile Ring Constriction in Fission Yeast

Cytokinesis involves constriction of a contractile actomyosin ring. The mechanisms generating ring tension and setting the constriction rate remain unknown because the organization of the ring is poorly characterized, its tension was rarely measured, and constriction is coupled to other processes. To isolate ring mechanisms, we studied fission yeast protoplasts, in which constriction occurs without the cell wall. Exploiting the absence of cell wall and actin cortex, we measured ring tension and imaged ring organization, which was dynamic and disordered. Computer simulations based on the amounts and biochemical properties of the key proteins showed that they spontaneously self-organize into a tension-generating bundle. Together with rapid component turnover, the self-organization mechanism continuously reassembles and remodels the constricting ring. Ring constriction depended on cell shape, revealing that the ring operates close to conditions of isometric tension. Thus, the fission yeast ring sets its own tension, but other processes set the constriction rate.

P48 Regulation of hydrogen sulfide in digestive stystem

Recently, we have studied the pathophysiological significance of H 2 S in the gastrointestinal diseases such as slow transmit constipation, intestinal I/R injury, abdominal infection, and omental arteries of human. We applied in vitro vascular ring tension measurement techniques by the means of measuring the tension of H 2 S and NO effects on human omental arteries ring tension, to reach the aims of exploring Regulation of H 2 S and NO in the blood vessels of adult omentum. The results showed that H 2 S and NO can relaxed human omental arteries with concentration-dependent; We also explore the possible relationship between H 2 S and the pathology of slow transmit constipation. We compound Diphenoxylate to set up the mice models of STC, and recorded the area under the curve (AUC) of spontaneous contractions and contraction frequency after drug additional to study the contraction of colonic tissues in vitro. The evidences showed that H 2 S has an obvious effect on colon smooth muscle contraction, and can increase the intestinal movements in slow transmit constipation. Our experiment states that H 2 S has anti-inflammation effect in prophase of acute peritoneal cavity infection. We used cecal ligation and puncture (CLP) to make up the rat models of acute peritoneal cavity infection, gave them different dispose include giving the donor of H 2 S, then observed the contents of TNF- α and H 2 S in serum and the content of MPO in intestinal tissues. And stated that H 2 S could alleviated CLP-induced inflammation obviously, decreased the content of TNF- α in serum when inflammation, and attenuate the infiltration of neutrophilic granulocyte in small intestine.

The effect of three-dimensional deformations of a cylinder liner on the tribological performance of a piston ring–cylinder liner system

This paper describes a numerical simulation model for prediction of the tribological effects of an oil control ring running against an out-of-round cylinder liner in a heavy duty diesel engine. The model considers the full three-dimensional geometry of the oil control ring and includes the effect of both surface roughness and global deformation. Results that test the model’s ability to do this under stationary conditions are presented. Furthermore, stationary results for prediction of the friction reduction possible by reduced ring tension in combination with reduced out-of-roundness are given. The model predicts the friction for the oil control ring at mid-stroke to be 78% larger in an out-of-round cylinder liner compared to a perfectly cylindrical one.