Tension Development Research Articles

Potentiation of Hypoxic Pulmonary Vasoconstriction by Hydrogen Sulfide Precursors 3-Mercaptopyruvate and D-Cysteine Is Blocked by the Cystathionine γ Lyase Inhibitor Propargylglycine.

Although the gasotransmitter hydrogen sulfide (H(2)S) generally dilates systemic arteries in mammals, it causes constriction of pulmonary arteries. In isolated rat pulmonary arteries, we have shown that the H(2)S precursor cysteine enhances both hypoxic pulmonary vasoconstriction and tension development caused by the agonist prostaglandin F(2α) under normoxic conditions. These effects were blocked by propargylglycine (PAG), a blocker of the enzyme cystathionine γ lyase which metabolises cysteine to sulfide. In the present study, we evaluated whether 3-mercaptopyruvate (3-MP), a sulfide precursor which is thought to give rise to sulfide when it is metabolised by the enzyme mercaptopyruvate sulfurtransferase, also enhanced contraction. Application of 3-MP prior to hypoxic challenge caused a marked enhancement of HPV which was completely blocked by both L- and D,L-PAG (both 1 mM). Cumulative application of 3-1,000 μM 3-MP during an ongoing contraction to PGF(2α) under normoxic conditions also caused a marked increase in tension. Application of D-cysteine (1 mM) also enhanced HPV, and this effect was prevented by both the D-amino acid oxidase inhibitor sodium benzoate (500 μM) and 1 mM L-PAG.

Gentrified sustainability: inequitable development and Seattle's skewed riskscape

This paper examines the tensions of sustainable development in Seattle, Washington, a commonly recognised urban environmental leader. Drawing on the perspective of sustainability as a conflicted process, this research expected a negative relationship between gentrification and environmental justice when affluent residents outcompete less affluent ones for neighbourhoods with fewer environmental hazards. The methods combine geographic cluster analysis and longitudinal air toxic emission comparisons to analyse socioeconomic changes in Seattle Census block-groups between 1990, 2000, and 2009 coupled with measures of relative potential risk and pollution volume. The property and development conflicts embedded within sustainability lead to pollution exposure risk and socioeconomic vulnerability converging in the same areas and reveal one of the 'Emerald City's' significant environmental challenges. Inequitable development and environmental injustice remain overlooked dimensions of sustainability that interdisciplinary research should address.

Influence of Simulated Microgravity on Mechanical Properties in the Human Triceps Surae Muscle in vivo

Purpose. The aim of the study was to investigate the effects of a simulated microgravity on the mechanical properties of the human triceps surae (TS) and to assess the effectiveness of physical training (PT) in preventing detrimental effects. Methods. Eight women (aged 26-36 years) underwent 120-d of Bed rest (BR): four underwent Bed rest only (BR group) and four performed PT during this period (BRPT group). The training sessions were conducted for 60 min each day for 6 days a week for 14 weeks, and 30-40 min twice a day for 2 weeks under the experiment conditions. PT was performed over a 4-d cycle: 3-d of training and 1-d of rest. The maximal voluntary contraction (MVC), and isometric twitch contraction (Pt), and electrically evoked tetanic tension at 150 impulses × s -1 (Ро), time-to-peak tension (TPT) of the twitch were determined. The difference between Ро and MVC expressed as a percentage of Ро and referred to a force deficiency (Рd). The MTS was determined according to the electromechanical delay (EMD) value during the explosive voluntary contraction. Surface electrodes sensed electromyographic (EMG) activity in the soleus muscle. Electromechanical delay (EMD) was the time interval between the change in EMG and movement muscle force production. Results. In the BR group, Рt, MVC, and Ро had decreased by 12, 36, 24%, respectively, but Рd had increased by 39%. TPT of the twitch had increased by 14%. The rate of increase of voluntary contractions reduced, but in the electrically evoked contraction no changes were observed. The EMD had increased by 27%. In the BREx group, МVС, Рt, and Ро decreased by 3%, and 14%, and 9%, respectively. TPT had decreased by 4%. The Pd had decreased significantly by 10%. The rate of rise increase of electrically evoked tetanic did not change significantly, but the rate of rise in isometric voluntary tension development was increased. The EMD had decreased by 12%. Conclusion. Unloading decreased function and EMD muscle and, although the PT did attenuate these effects, they did not completely prevent them. It is suggested that the total loading volume (mainly its intensity) was not sufficient to completely prevent alterations in tendon mechanical properties

Development of Warp Yarn Tension During Shedding: A Theoretical Approach

Theoretical investigation on the process of development of warp yarn tension during weaving for tappet shedding is carried out, based on the dynamic nature of shed geometry. The path of warp yarn on a weaving machine is divided into four different zones. The tension developed in each zone is estimated for every minute rotation of the bottom shaft. A model has been developed based on the dynamic nature of shed geometry and the possible yarn flow from one zone to another. A computer program, based on the model of shedding process, is developed for predicting the warp yarn tension variation during shedding. The output of the model and the experimental values of yarn tension developed in zone-D i.e. between the back rest and the back lease rod are compared, which shows a good agreement between them. The warp yarn tension values predicted by the model in zone-D are 10–13 % lesser than the experimentally measured values. By analyzing the theoretical data of the peak value of developed yarn tension at four zones i.e. zone-A, zone-B, zone-C and zone-D, it is observed that the peak yarn tension value of A, B, C-zones are much higher than the peak tension near the back rest i.e. at zone-D. It is about twice or more than the yarn tension near the back rest. The study also reveals that the developed yarn tension peak values are different for the extreme positions of a heald. The impact of coefficient of friction on peak value of yarn tension is nominal.

A novel role for RhoA GTPase in the regulation of airway smooth muscle contraction.

Recent studies have demonstrated a novel molecular mechanism for the regulation of airway smooth muscle (ASM) contraction by RhoA GTPase. In ASM tissues, both myosin light chain (MLC) phosphorylation and actin polymerization are required for active tension generation. RhoA inactivation dramatically suppresses agonist-induced tension development and completely inhibits agonist-induced actin polymerization, but only slightly reduces MLC phosphorylation. The inhibition of MLC phosphatase does not reverse the effects of RhoA inactivation on contraction or actin polymerization. Thus, RhoA regulates ASM contraction through its effects on actin polymerization rather than MLC phosphorylation. Contractile stimulation of ASM induces the recruitment and assembly of paxillin, vinculin, and focal adhesion kinase (FAK) into membrane adhesion complexes (adhesomes) that regulate actin polymerization by catalyzing the activation of cdc42 GTPase by the G-protein-coupled receptor kinase-interacting target (GIT) - p21-activated kinase (PAK) - PAK-interacting exchange factor (PIX) complex. Cdc42 is a necessary and specific activator of the actin filament nucleation activator, N-WASp. The recruitment and activation of paxillin, vinculin, and FAK is prevented by RhoA inactivation, thus preventing cdc42 and N-WASp activation. We conclude that RhoA regulates ASM contraction by catalyzing the assembly and activation of membrane adhesome signaling modules that regulate actin polymerization, and that the RhoA-mediated assembly of adhesome complexes is a fundamental step in the signal transduction process in response to a contractile agonist.

Weekly versus monthly testosterone administration on fast and slow skeletal muscle fibers in older adult males.

In older adults, loss of mobility due to sarcopenia is exacerbated in men with low serum T. T replacement therapy is known to increase muscle mass and strength, but the effect of weekly (WK) vs monthly (MO) administration on specific fiber types is unknown. To determine the efficacy of WK vs MO T replacement on the size and functional capacity of individual fast and slow skeletal muscle fiber types. Subjects were randomized into a 5-month, double-blind, placebo-controlled trial. All subjects (ages, 61-71 y) were community-dwelling men who had T levels < 500 ng/dL. Subjects were dosed weekly for 5 months, receiving continuous T (WK, n = 5; 100 mg T enanthate, im injection), monthly cycled T (MO, n = 7; alternating months of T and placebo), or placebo (n = 7). Muscle biopsies of the vastus lateralis were obtained before and after treatment. Main outcomes for individual slow and fast fibers included fiber diameter, peak force (P0), rate of tension development, maximal shortening velocity, peak power, and Ca(2+) sensitivity. Both treatments increased fiber diameter and peak power, with WK treatment 5-fold more effective than MO in increasing type I fiber P0. WK effects on fiber diameter and force were 1.5-fold higher in slow fibers compared to fast fibers. In fast type II fibers, diameter and P0 increased similarly between treatments. The increased power was entirely due to increased fiber size and force. In conclusion, T replacement effects were fiber-type dependent, restricted to increases in cell size, P0, and peak power, and dependent on the paradigm selected (WK vs MO).

Pathomechanisms in heart failure: the contractile connection.

Heart failure is a multi-factorial progressive disease in which eventually the contractile performance of the heart is insufficient to meet the demands of the body, even at rest. A distinction can be made on the basis of the cause of the disease in genetic and acquired heart failure and at the functional level between systolic and diastolic heart failure. Here the basic determinants of contractile function of myocardial cells will be reviewed and an attempt will be made to elucidate their role in the development of heart failure. The following topics are addressed: the tension generating capacity, passive tension, the rate of tension development, the rate of ATP utilisation, calcium sensitivity of tension development, phosphorylation of contractile proteins, length dependent activation and stretch activation. The reduction in contractile performance during systole can be attributed predominantly to a loss of cardiomyocytes (necrosis), myocyte disarray and a decrease in myofibrillar density all resulting in a reduction in the tension generating capacity and likely also to a mismatch between energy supply and demand of the myocardium. This leads to a decline in the ejection fraction of the heart. Diastolic dysfunction can be attributed to fibrosis and an increase in titin stiffness which result in an increase in stiffness of the ventricular wall and hampers the filling of the heart with blood during diastole. A large number of post translation modifications of regulatory sarcomeric proteins influence myocardial function by altering calcium sensitivity of tension development. It is still unclear whether in concert these influences are adaptive or maladaptive during the disease process.

Simulations of texture evolution for HCP metals: Influence of the main slip systems

Deformation of hexagonal close packed (HCP) metals is accompanied by the development of a strong texture, which depends on the predominant deformation mechanism of the metal and the deformation path. This study investigates texture rotations in HCP deforming by basal 〈a〉 , prismatic 〈a〉 , pyramidal 〈a〉 or pyramidal 〈c+a〉 slip. This study uses crystal plasticity models to simulate the development of tension, compression and plane strain deformation textures. Basal slip causes rotation of the 〈c〉 axis toward the compression direction, as well as pyramidal 〈a〉 slip, whereas pyramidal 〈c+a〉 slip makes the 〈c〉 axis rotate toward the extension direction. Prismatic slip generates a rotation of the lattice around its 〈c〉 axis, but the 〈c〉 axis position does not change; however a prismatic plane rotates toward the extension direction. The development of textures in constrained crystals deforming with multiple slip modes is compared with the effect of the dominant slip system activity.

Low-dose ouabain administration increases Na+,K+-ATPase activity and reduces cardiac force development in rats

BackgroundOuabain is a digitalis compound that inhibits the Na+,K+-ATPase (NKA) activity inducing increment in cardiac force. However, this effect seems to be dose dependent. At low concentration, ouabain can induce an increase of NKA activity. MethodsWe investigated the effects of ouabain administration (25μg/kg/day) for 15 days on cardiac contractility and NKA activity. Blood pressure and left ventricular papillary muscle contraction from placebo and ouabain-treated rats for 15 (OUA15) days were evaluated. Isometric force, post-rest potentiation, positive inotropic intervention produced by isoproterenol, and tetanic tension were measured. The activity and protein expression levels of α1 and α2 isoforms of NKA, sodium calcium exchanger (NCX), sarcoplasmic reticulum calcium ATPase (SERCA2a) and phospholamban (PLB) were also measured. ResultsSystolic and diastolic blood pressures increased after treatment with ouabain. However, isometric tension was reduced in the ouabain treated group. Post-rest potentiation, time parameters, inotropic interventions by isoproterenol and tetanic tension did not change. In the ouabain treated group, NKA activity was increased (Oua 406.16±70.6 vs. CT 282.80±80.5) while protein expression of the α1 isoform of NKA was reduced (Oua 0.97±0.06 vs. CT 0.76±0.05). No changes were observed in protein expression of α2 isoform of NKA, NCX, SERCA2a and PLB. Therefore, although 15-day ouabain treatment increases blood pressure (Oua: 116.4±3 vs. CT: 99.9±3), treatment also reduces isometric tension development (Oua: 0.34±0.14 vs. CT: 0.56±0.22). ConclusionWe suggest that the effects induced by ouabain in the isolated cardiac muscle could be related at least in part, to changes in NKA activity.

ACUTE KIDNEY INJURY DECREASED ENDOGENOUS HYDROGEN SULFIDE PRODUCTION AND INCREASED CYTOKINE EXPRESSION: IMPACT ON CARDIOVASCULAR SYSTEM

BACKGROUND: In some pathologic circumstances (e.g., septicemia) nitric oxide (NO) synthesis is higher and it is implicated in lowering of the blood pressure that usually is less responsive to conventional therapy with adrenaline and vasopressin. Thus, new specific therapeutic approaches using high affinity NO scavengers are of great relevance. Accordingly, some new ruthenium compounds with this putative property were synthesized. The aim of this work was to evaluate the NO scavenging activity of those compounds. METHODS: Aorta rings obtained from the thoracic aorta of adult male Wistar rats were suspended under 60% of maximal tension in an organ bath, containing 15 mL of Krebs-Henseleit solution (36.5 0.1oC, pH 7.2-7.4, gassed with 95% O2:5% CO2). After 60 min stabilization period, maximum contraction of aortic rings was obtained in response to noradrenaline. After that, acetylcholine was added in order to obtain maximal relaxation. Cumulative concentration-response curves were obtained to the compounds: trans-[Ru(NH3)4(SO4)(4-picoline)](BF4) (Ru-pic); trans-[Ru(NH3)4 (SO4) (nicotinamida)](BF4) (Ru-ina); trans-[Ru(NH3)4(SO4) (isonicotina mide)] (BF4) (Ru-isn); [Ru(NH3)5Cl]Cl2 (Ru-Cl); [Ru(edta)Cl] (RuEDTA); cis-[Ru(NH3)4oxalato](TFMS)3 (Ru-cis-Ox); cis[Ru(NH3)4(H2O)2 (TFMS)3 (Ru-cis-aquo) and trans [Ru(NH3)5(H2O)(TFMS)3 (Ru-trans-aquo). The same procedure was performed in the presence of L-NAME, an inhibitor of nitric oxide synthase. Control rings were not exposed to any ruthenium compound. RESULTS: The mean sem of the tension developed by the tissues following exposition to noradrenaline was 1.94 0.17 gf. Acetylcholine reduced the developed tension to 0.17 0.04 gf. In the presence of the all Ru-compounds, the developed tensions (gf) were: 1.68 0.19 (Ru-pic; n1⁄45); 1.43 0.15 (Ru-isn; n1⁄45); 1.47 0.16 (Ru-ina; n1⁄45); 1.74 0.13 (Ru-EDTA; n1⁄45); 2.93 0.24 (Ru-Cl; n1⁄45); 2.85 0.07 (Ru-cis-Ox; n1⁄45); 3.08 0.15 (Ru-cis-aquo; n1⁄45); 3.12 0.12 (Ru-trans-aquo; n1⁄45); [p<0.05 compared to control, Student t test]. All the analyzed compounds were able to cancel the effect of acetylcholine and had similar potencies (pD2; mean sem): 5.60 0.18 (Ru-pic); 5.34 0.25 (Ru-isn); 5.40 0.27 (Ru-ina); 5.48 0.23 (Ru-Cl); 6.45 0.39 (Ru-EDTA); 5.19 0.30 (Ru-cis-Ox); 5.59 0.24 (Ru-cis-aquo); 5.03 0.37 (Ru-trans-aquo). None of the effects of acetylcholine or compounds were observed when they were tested in the presence of L-NAME. CONCLUSION: The data suggested that all compounds were able to scavenge NO in rat aortic rings and to restore the vascular tone.

Is contraction-stimulated glucose transport feedforward regulated by Ca2+?

In many cell types, Ca(2+) signals to increase the movement and surface membrane insertion of vesicles. In skeletal muscle, Ca(2+) is predominantly released from the sarcoplasmic reticulum (SR) to initiate contraction. Sarcoplasmic reticulum Ca(2+) release is widely believed to be a direct feedforward regulator of the translocation of glucose transporter4 to the cell surface to facilitate transmembrane glucose transport. This review summarizes the evidence supporting the Ca(2+) feedforward model and its proposed signalling links to regulation of glucose transport in skeletal muscle and other cell types. The literature is contrasted against our recent findings suggesting that SR Ca(2+) release is neither essential nor adequate to stimulate glucose transport in muscle. Instead, feedback signals through AMPK and mechanical stress are likely to account for most of contraction-stimulated glucose transport. A revised working model is proposed, in which muscle glucose transport during contraction is not directly regulated by SR Ca(2+) release but rather responds exclusively to feedback signals activated secondary to cross-bridge cycling and tension development.

Planetary boundaries: at the threshold… again: sustainable development ideas and politics

The implications of the planetary boundaries (PBs) proposal involves scientific, moral and political dimensions. The core of the PBs idea is that humankind is transgressing global environmental tipping points resulting in changed conditions that threaten to unravel human progress. The growing status of the proposal potentially makes it a highly influential organising concept that seems to contain within it aspirations to dramatically reconstitute the relationship between society and the environment—thereby transforming the politics of sustainable development. This paper situates PBs in contemporary green thinking. Key planning events and related documents supporting the Post-2015 Development Agenda process are then examined to identify strategies and reactions to the PB proposal. The findings show that divisions reminiscent of older North/South environment and development tensions related to the role of experts, democracy and the Right to Development threaten to prevent PBs from being mainstreamed in key UN environment and development programmes and fora.

Abstract MP06: The Protein Tyrosine Phosphatase Inhibitors Induce The Vasoconstriction Via Src/epidermal growth factor/rho-kinase Cascade

Orthovanadate (OVA), a protein tyrosine phosphatase (PTPase) inhibitor, exerts contractile effects on smooth muscle in a Rho-kinase-dependent manner, but the precise mechanisms are not elucidated. The aim of this study was to determine the potential roles of Src and epidermal growth factor receptor (EGFR) in the OVA-induced contraction of rat aortas and the phosphorylation of myosin phosphatase target subunit 1 (MYPT1; an index of Rho-kinase activity) in vascular smooth muscle cells (VSMCs). The concentration-response curves for OVA (8–1000μM) were constructed in endothelium-denuded rings using stepwise increases in the concentration of OVA, and the maximal force was observed at concentrations of &gt;500 μM (16 ± 2 in % of 60 mmol/L KCl). OVA (500 μM) evoked rapid contraction of endothelium-denuded aortas, presenting as a hyperbolic rise in tension development within 10 min followed by a slow linear rise. Aortic contraction by OVA was significantly blocked not only by Rho kinase inhibitors Y-27632 and hydroxyfasudil, but also by Src inhibitors PP2 and Src inhibitor No. 5 and the EGFR inhibitors AG1478 and EGFR inhibitor 1. OVA induced rapid increases in the phosphorylation of MYPT1 (Thr-853; 180 ± 24 % in OVA vs 98 ± 22 in vehicle), Src (Tyr-416; 225 ± 34 % in OVA vs 102 ± 30 in vehicle), and EGFR (Tyr-1173; 173 ± 31 % in OVA vs 101 ± 18 in vehicle) in VSMCs, and Src inhibitors abolished these effects. OVA-induced Src phosphorylation was abrogated by Src inhibitors, but not affected by inhibitors of EGFR and Rho-kinase. Inhibitors of Src and EGFR, but not Rho-kinase, also blocked OVA-induced EGFR phosphorylation. Furthermore, a metalloproteinase inhibitor TAPI-0 and an inhibitor of heparin-binding EGF not only abrogated the OVA-induced aortic contraction, but also OVA-induced EGFR and MYPT1 phosphorylation, suggesting the involvement of EGFR transactivation. OVA also induced EGFR phosphorylation at Tyr-845, one of residues phosphorylated by Src. These results suggest that OVA-induced vasocontraction is mediated by the Rho-kinase-dependent inactivation of myosin light chain phosphatase via signaling downstream of Src-induced transactivation of EGFR.

Research on Tension Control System of Wire Saw Slicing Machine

Nowadays, wire sawing becomes the most advanced brittle crystals slicing technology because of its advantages of slicing larger crystals ingots into very small thickness, high surface quality, high yield wafers. In the process, the thin wire, which is the processing tools, travels at high speed, and subjects to external excitation from many aspects. Wire saw tension control is the core and difficulty of the control system. Mathematical models of tension subsystems were studied. The control strategy of swing arm motor tension direct closed-loop combination of speed difference indirect closed-loop was proposed. The developed tension control hardware and software system reached the functional requirements and technical indicators, and constant tension precision control was solved effectively.

Indirect evidence for elastic energy playing a role in limb recovery during toad hopping.

Elastic energy is critical for amplifying muscle power during the propulsive phase of anuran jumping. In this study, we use toads (Bufo marinus) to address whether elastic recoil is also involved after take-off to help flex the limbs before landing. The potential for such spring-like behaviour stems from the unusually flexed configuration of a toad's hindlimbs in a relaxed state. Manual extension of the knee beyond approximately 90° leads to the rapid development of passive tension in the limb as underlying elastic tissues become stretched. We hypothesized that during take-off, the knee regularly extends beyond this, allowing passive recoil to help drive limb flexion in mid-air. To test this, we used high-speed video and electromyography to record hindlimb kinematics and electrical activity in a hindlimb extensor (semimembranosus) and flexor (iliofibularis). We predicted that hops in which the knees extended further during take-off would require less knee flexor recruitment during recovery. Knees extended beyond 90° in over 80% of hops, and longer hops involved greater degrees of knee extension during take-off and more intense semimembranosus activity. However, knee flexion velocities during recovery were maintained despite a significant decrease in iliofibularis intensity in longer hops, results consistent with elastic recoil playing a role.

Selective regulation of cytoskeletal tension and cell–matrix adhesion by RhoA and Src

The crosstalk between cells and their microenvironment enables cellular adaptation to external mechanical cues through the remodeling of cytoskeletal structures and cell-matrix adhesions to ensure normal cell function. This study investigates the relationship between the cytoskeletal tension and integrin α5β1 adhesion strength to the matrix (i.e. fibronectin) in the context of RhoA-Src crosstalk. Integration of atomic force microscopy (AFM) with total internal reflection fluorescence and spinning-disk confocal microscopy enabled acquisition of complementary structural and functional measurements on live vascular smooth muscle cells expressing RhoA and c-Src variants (wild-type, dominant negative, constitutively active). Single ligand-receptor interaction measurements performed with AFM probes functionalized with fibronectin showed that RhoA and c-Src activation have different effects on cytoskeletal tension development, inducing two distinct force-stiffness functional regimes for α5β1-integrin binding to fibronectin. Moreover, fluorescence measurements showed that c-Src activation had a modest effect on actin morphology, while RhoA significantly modulated stress fiber formation. In addition, c-Src was associated with regulation of myosin light chain (MLC) phosphorylation, suggesting a c-Src-dependent modulation of RhoA pathway through activation of downstream effectors. Therefore, c-Src may be a possible component of cytoskeletal tension regulation through MLC activation. Our findings suggest that Src and RhoA coordinate a regulatory network that determines cytoskeletal tension through activation of actomyosin contractility. In turn, the cytoskeletal tension state modulates integrin α5β1-fibronectin adhesion force.

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.

Timing and magnitude of systolic stretch affect myofilament activation and mechanical work.

Dyssynchronous activation of the heart leads to abnormal regional systolic stretch. In vivo studies have suggested that the timing of systolic stretch can affect regional tension and external work development. In the present study, we measured the direct effects of systolic stretch timing on the magnitude of tension and external work development in isolated murine right ventricular papillary muscles. A servomotor was used to impose precisely timed stretches relative to electrical activation while a force transducer measured force output and strain was monitored using a charge-couple device camera and topical markers. Stretches taking place during peak intracellular Ca(2+) statistically increased peak tension up to 270%, whereas external work due to stretches in this interval reached values of 500 J/m. An experimental analysis showed that time-varying elastance overestimated peak tension by 100% for stretches occurring after peak isometric tension. The addition of the force-velocity relation explained some effects of stretches occurring before the peak of the Ca(2+) transient but had no effect in later stretches. An estimate of transient deactivation was measured by performing quick stretches to dissociate cross-bridges. The timing of transient deactivation explained the remaining differences between the model and experiment. These results suggest that stretch near the start of cardiac tension development substantially increases twitch tension and mechanical work production, whereas late stretches decrease external work. While the increased work can mostly be explained by the time-varying elastance of cardiac muscle, the decreased work in muscles stretched after the peak of the Ca(2+) transient is largely due to myofilament deactivation.

Hypoxic pulmonary hypertension: the paradigm is changing.

Hypoxic pulmonary hypertension: the paradigm is changing.

Leading and Learning in the Psychotherapy Supervision Seminar: Some Thoughts on the Beginnings of Supervisor Development

Supervisor development theories typically give focus to growth of the supervisor via practice. But in what ways does the foundational psychotherapy supervision seminar stimulate and first set in motion the supervisor development process? That question is subsequently considered. Based on personal experience in training supervisors via seminars and ongoing reflection about that learning process, five seminar-induced themes that potentially reflect beginning tensions of supervisor development are proposed, and their seeming evolution over the course of the supervision seminar is considered. Points that are raised include the following: (a) the supervision seminar is the first, primary stimulus of supervisor development and sets the stage for later growth via practice; (b) early themes that are identified in supervisor development theories also make appearance in the supervision seminar experience; (c) to best understand the full arc of supervisor development, the seminar as both developmental initiator and intervention preparedness foundation merits more careful scrutiny; and (d) through more completely understanding the seminar as instigator of supervisor development, supervisor educators might be better positioned to develop seminars that most constructively affect the very beginnings of the supervisor development process.