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排序方式: 共有155条查询结果,搜索用时 724 毫秒
1.
H. P. J. Buschman M. Linari G. Elzinga R. C. Woledge 《Pflügers Archiv : European journal of physiology》1997,435(1):145-150
The mechanical and energy characteristics of isolated fast-twitch muscle fibres (type 1) of Xenopus laevis in isometric- and isovelocity contractions were measured at 20°C. The fibres were stimulated at either 60 Hz or 20 Hz to
produce contractions at different levels of activation. The high stimulation frequency gave fused contractions, while at the
low stimulation frequency tension fluctuated. When maximum isometric force had been reached, the fibres were shortened by
10% of the fibre length at different velocities. At 60 Hz stimulation during shortening the rate of heat production increased
above the isometric rate of heat production. At 20 Hz stimulation during shortening, however, the rate of heat production
was not different from the isometric rate of heat production. Mechanical efficiency was the same at the high and low level
of activation. The actomyosin efficiency (i.e. the mechanical efficiency corrected for ”activation heat”) was highest at the
low level of activation. We conclude that in fast-twitch muscle fibres from X. laevis, actomyosin efficiency is highest for partially activated muscle. From a comparison of the present results with those obtained
from a study of slow-twitch muscle fibres presented earlier, it is concluded that fast-twitch muscle fibres are less efficient
than slow-twitch muscle fibres.
Received after revision: 13 May 1997 / Accepted: 1 July 1997 相似文献
2.
Shin-ya Kuno Mitsuharu Inaki Kiyoji Tanaka Yuji Itai Katsumi Asano 《European journal of applied physiology》1994,69(4):301-304
Four well-trained combination skiers were studied through pre- and post-training for the effects of short-term intermittent training during hypoxia on muscle energetics during submaximal exercise as measured by Phosphorus-31 nuclear magnetic resonance and maximal aerobic power (
O2max). The hypoxia and training in the cold was conducted in a hypobaric chamber and comprised 60-min aerobic exercise (at an intensity equivalent to the blood lactate threshold), using a cycle ergometer or a treadmill twice a day for 4, consecutive days at 5°C, in conditions equivalent to an altitude of 2000 m (593 mm Hg). No change in
O2max was observed over the training period, while in the muscle energetics during submaximal exercise, the values of phosphocreatine/(phosphocreatine + inorganic phosphate) and intracellular pH were found to be significantly increased by training during hypoxia. During recovery, the time constant of phosphocreatine was found to have been significantly reduced [pre, 27.9 (SD 6.7) s; post, 22.5 (SD 4.7) s, P < 0.01]. The observed inhibition of phosphocreatine as well as that of intracellular pH changes after training during hypoxia and quicker recovery of phosphocreatine in submaximal exercise tests, may indicate improved oxidative capacity (i.e. a high adenosine 5-triphosphate formation rate) despite the short-term hypoxia training.
Present address: Department Life Sciences, Univ. of Tokyo, Komaba 3-8-1, Meguro-ku 153, Japan 相似文献
3.
An adenoviral vector expressing the glucose transporter protects cultured striatal neurons from 3-nitropropionic acid 总被引:2,自引:0,他引:2
Considerable interest has focused on the possibility of using gene transfer techniques to introduce protective genes into neurons around the time of necrotic insults. We have previously used herpes simplex virus amplicon vectors to overexpress the rat brain glucose transporter, Glut-1 (GT), and have shown it to protect against a variety of necrotic insults both in vitro and in vivo, as well as to buffer neurons from the steps thought to mediate necrotic injury. It is critical to show the specificity of the effects of any such transgene overexpression, in order to show that protection arises from the transgene delivered, rather than from the vector delivery system itself. As such, we tested the protective potential of GT overexpression driven, in this case, by an adenoviral vector, against a novel insult, namely exposure of primary striatal cultures to the metabolic poison, 3-nitropropionic acid (3NP). We observed that GT overexpression buffered neurons from neurotoxicity induced by 3NP. 相似文献
4.
《Gait & posture》2022
BackgroundIndividuals with lower limb amputation exhibit lower residual limb strength compared to their sound limb. Deficits in residual limb knee flexion and extension strength may impact functional performance during tasks relevant to daily living.Research questionDoes knee flexor and extensor strength in the residual limb impact functional outcome measures, such as walking energetics and performance metrics, in individuals with unilateral transtibial amputation?MethodsFourteen individuals with traumatic unilateral transtibial amputation were recruited for this observational study. Participants completed metabolic testing at three standardized speeds based on leg length, as well maximum isokinetic knee flexion and extension strength for both residual and sound limbs. Participants also completed a series of functional outcome tests, including a two-minute walk test, timed stair ascent test, and four-square step test. Walking energetics (metabolic cost, heart rate, and rating of perceived exertion) and performance metrics were compared to percent deficit of residual limb to sound limb knee flexion and extension muscle strength. A linear regression assessed significant relationships (p < 0.05).ResultsA significant relationship was observed between percent deficit of knee extension strength and heart rate (p = 0.024) at a fast walking speed. Additionally, percent deficit knee flexion strength related to rating of perceived exertion at slow and moderate walking speeds (p = 0.038, p = 0.024). Percent deficit knee extension strength related to two-minute walk time performance (p = 0.035) and percent deficit knee flexion strength related to timed stair ascent time (p = 0.025).SignificanceThese findings suggest the importance of strength retention of the residual limb knee flexion and extension musculature to improve certain functional outcomes in individuals with unilateral transtibial amputation. 相似文献
5.
Summary We have recently shown that the mechanical efficiency of the contractile machinery of the canine left ventricle is constant at 30%–50%, independent of its loading, heart rate, and inotropic conditions. In contrast, the conventional mechanical efficiency of the ventricle is known to vary between 0 and 30%, depending on these conditions. In this study, we derived an equation for the conventional mechanical efficiency as a function of ventricular preload, afterload, and contractility, based on the constant mechanical efficiency of the contractile machinery. In deriving this equation, we fully utilized our new concept of the total mechanical energy of the left ventricle, i.e., systolic pressure-volume area, and our recent findings of the linear relationship between left ventricular oxygen consumption and the systolic pressure-volume area as well as the dependence of this relation on the ventricular inotropic state. As a result, the conventional mechanical efficiency of the left ventricle was found to change between 0 and 25% as an explicit function of these cardiodynamic and inotropic conditions. Using this function, we obtained combinations of loading and inotropic conditions to maximize the conventional mechanical efficiency of the left ventricle. 相似文献
6.
S M Davidson G D Lopaschuk M Spedding P M Beart 《British journal of pharmacology》2014,171(8):1795-1797
While the mitochondrion has long fascinated biologists and the sheer diversity of druggable targets has made it attractive for potential drug development, there has been little success translatable to the clinic. Given the diversity of inborn errors of metabolism and mitochondrial diseases, mitochondrially mediated oxidative stress (myopathies, reperfusion injury, Parkinson''s disease, ageing) and the consequences of disturbed energetics (circulatory shock, diabetes, cancer), the potential for meaningful gain with novel drugs targeting mitochondrial mechanisms is huge both in terms of patient quality of life and health care costs. In this themed issue of the British Journal of Pharmacology, we highlight the key directions of the contemporary advances in the field of mitochondrial biology, emerging drug targets and new molecules which are close to clinical application. Authors'' contributions are diverse both in terms of species and organs in which the mitochondrially related studies are performed, and from the perspectives of mechanisms under study. Defined roles of mitochondria in disease are updated and previously unknown contributions to disease are described in terms of the interface between basic science and pathological relevance.
Linked Articles
This article is part of a themed issue on Mitochondrial Pharmacology: Energy, Injury & Beyond. To view the other articles in this issue visit http://dx.doi.org/10.1111/bph.2014.171.issue-8 相似文献7.
Stanislaw Pogorzelski Katarzyna Boniewicz-Szmyt Maciej Grzegorczyk Pawel Rochowski 《Materials》2022,15(5)
The aim of the work was to quantify the surface wettability of metallic (Fe, Al, Cu, brass) surfaces covered with sprayed paints. Wettability was determined using the contact angle hysteresis approach, where dynamic contact angles (advancing ΘA and receding ΘR) were identified with the inclined plate method. The equilibrium, ΘY, contact angle hysteresis, CAH = ΘA − ΘR, film pressure, Π, surface free energy, γSV, works of adhesion, WA, and spreading, WS, were considered. Hydrophobic water/solid interactions were exhibited for the treated surfaces with the dispersive term contribution to γSV equal to (0.66–0.69). The registered 3D surface roughness profiles allowed the surface roughness and surface heterogeneity effect on wettability to be discussed. The clean metallic surfaces turned out to be of a hydrophilic nature (ΘY < 90°) with high γSV, heterogeneous, and rough with a large CAH. The surface covering demonstrated the parameters’ evolution, ΘA↑, ΘR↑, γSV↓, WA↓, and WS↓, corresponding to the surface hydrophobization and exhibiting base substratum-specific signatures. The dimensionless roughness fluctuation coefficient, η, was linearly correlated to CAH. The CAH methodology based on the three measurable quantities, ΘA, ΘR, and liquid surface tension, γLV, can be a useful tool in surface-mediated process studies, such as lubrication, liquid coating, and thermoflow. 相似文献
8.
Purpose. To characterize the surface thermodynamic properties of two polymorphic forms (I and II) of salmeterol xinafoate (SX) prepared from supercritical fluids and a commercial micronized SX (form I) sample (MSX).
Methods. Inverse gas chromatographic analysis was conducted on the SX samples at 30, 40, 50, and 60°C using the following probes at infinite dilution: nonpolar probes (NPs; alkane C5-C9 series); and polar probes (PPs; i.e., dichloromethane, chloroform, acetone, ethyl acetate, diethyl ether, and tetrahydrofuran). Surface thermodynamic parameters of adsorption and Hansen solubility parameters were calculated from the retention times of the probes.
Results. The free energies of adsorption (-GA) of the three samples obtained at various temperatures follow this order: SX-II > MSX SX-I for the NPs; and SX-II > MSX > SX-I for the PPs. For both NPs and PPs, SX-II exhibits a less negative enthalpy of adsorption (HA) and a much less negative entropy of adsorption (SA) than MSX and SX-I, suggesting that the high -GA of SX-II is contributed by a considerably reduced entropy loss. The dispersive component of surface free energy (s
D) is the highest for MSX but the lowest for SX-II at all temperatures studied, whereas the specific component of surface free energy of adsorption (-GA
SP) is higher for SX-II than for SX-I. That SX-II displays the highest -GA for the NP but the lowest s
D of all the SX samples may be explained by the additional -GA change associated with an increased mobility of the probe molecules on the less stable and more disordered SX-II surface. The acid and base parameters, KA and KD, that were derived from HA
SP reveal significant differences in the relative acid and base properties among the samples. The calculated Hansen solubility parameters (D, P, and H) indicate that the surface of SX-II is the most polar and most energetic of all the three samples in terms of specific interactions (mostly hydrogen bonding).
Conclusions. The metastable SX-II polymorph possesses a higher surface free energy, higher surface entropy, and a more polar surface than the stable SX-I polymorph. 相似文献
9.
Pan JW Kim JH Cohen-Gadol A Pan C Spencer DD Hetherington HP 《Acta neurologica Scandinavica》2005,111(4):218-224
OBJECTIVES: There is increasing evidence for a dysfunctional metabolic network in human mesial temporal lobe epilepsy (MTLE). To further describe this, we evaluated the bioenergetic status in unilateral MTLE inter-regionally and in relation to neuropathology. MATERIALS AND METHODS: We used whole brain high field (4 T) 31P MR spectroscopic imaging to determine in vivo PCr and ATP, studying n=22 patients (all candidates for hippocampal resection) and n=14 control volunteers. The degree of bioenergetic impairment was assessed by calculating the ratio of PCr to ATP. RESULTS: Compared to controls, patients demonstrated significant decreases in PCr/ATP from the ipsilateral amygdala and pes (0.84 +/- 0.14, 0.87 +/- 0.10, respectively, patients vs 0.97 +/- 0.15, 0.98 +/- 0.16, controls). In patients, the ipsilateral thalamic energetics positively correlated with contralateral hippocampal energetics. In addition, the ipsilateral thalamic and striatal energetics negatively correlated with hippocampal total glial counts. CONCLUSIONS: These data are consistent with a view that in MTLE, the bilateral hippocampi, ipsilateral thalamus and striatum are linked in their energetic depression, possibly reflecting the propagation of seizures throughout the brain. 相似文献
10.
Adaptive evolution of cytochrome c oxidase: Infrastructure for a carnivorous plant radiation
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Jobson RW Nielsen R Laakkonen L Wikström M Albert VA 《Proceedings of the National Academy of Sciences of the United States of America》2004,101(52):18064-18068
Much recent attention in the study of adaptation of organismal form has centered on developmental regulation. As such, the highly conserved respiratory machinery of eukaryotic cells might seem an unlikely target for selection supporting novel morphologies. We demonstrate that a dramatic molecular evolutionary rate increase in subunit I of cytochrome c oxidase (COX) from an active-trapping lineage of carnivorous plants is caused by positive Darwinian selection. Bladderworts (Utricularia) trap plankton when water-immersed, negatively pressured suction bladders are triggered. The resetting of traps involves active ion transport, requiring considerable energy expenditure. As judged from the quaternary structure of bovine COX, the most profound adaptive substitutions are two contiguous cysteines absent in approximately 99.9% of databased COX I sequences from Eukaryota, Archaea, and Bacteria. This motif lies directly at the docking point of COX I helix 3 and cytochrome c, and modeling of bovine COX I suggests the possibility of an unprecedented helix-terminating disulfide bridge that could alter COX/cytochrome c dissociation kinetics. Thus, the key adaptation in Utricularia likely lies in molecular energetic changes that buttressed the mechanisms responsible for the bladderworts' radical morphological evolution. Along with evidence for COX evolution underlying expansion of the anthropoid neocortex, our findings underscore that important morphological and physiological innovations must often be accompanied by specific adaptations in proteins with basic cellular functions. 相似文献