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781.
D. H. Weinstein 《Journal of biological physics》1993,19(3):189-197
The ability of ATP powered motor proteins to convert chemical free energy into the mechanical work required to move intra-cellular organelles is discussed in terms of the molecular and dynamic fundamentals involved in producing such movements. This is carried out in detail for muscle contraction with the result that in order for a myosin head to act as a motor protein, it is necessary for it to be able to impose a unique series of impacts on an actin filament. It is further shown that these impacts can be generated when a single water molecule is transiently attached to the ADP formed during one step of an ATP cycle in the myosin head. This analysis leads to the conclusion that muscle must be a type of heat machine which has the capability of attaining mechanochemical efficiencies that approach 100%. An extension of ATP powered motor proteins in general is made with the finding that they must share the same motor mechanism of the transiently attached water molecule. A possible application of these considerations to the problem of the active transport of ions is also pointed out. 相似文献
782.
Zhixin Zhang Stefano Mammola Zhiqiang Liang César Capinha Qiwei Wei Yuanan Wu Jin Zhou Chongrui Wang 《Freshwater Biology》2020,65(5):971-980
- Being the largest extant amphibian in the world, the IUCN Critically Endangered Chinese giant salamander Andrias davidianus is a charismatic species with great international public interest. While threats such as commercial overexploitation and habitat degradation have been extensively documented to affect natural populations of A. davidianus, still no information is available about the species sensitivity to climate change.
- Here, we develop an ensemble of species distribution models (SDMs) for A. davidianus and projected its habitat suitability under present-day and future climate change scenarios. We based our SDMs on bioclimatic and topographic predictors, and recent (2012–2018) field-collected occurrence data across the whole distribution range of the species.
- The ensemble SDMs exhibited good predictive capacity and suggested that slope, maximum temperature of warmest month, precipitation of driest month, and isothermality are the most influential predictors in determining distribution patterns in this species. The projections of our models point to a pronounced impact of climate changes over A. davidianus, with more than two-thirds of its suitable range expected to be lost in all scenarios of future climates tested.
- In concert with the numerous other threats that are affecting this species, climate change poses a serious hindrance to the long-term survival of A. davidianus. We emphasise the urgent need of undertaking strict measures to manage this species and safeguard the few remaining available suitable habitats. We suggest that adaptive management strategies including designation of new reserves should be considered to mitigate the impacts of climate change on A. davidianus.
783.
A. Y. Belanger A. J. McComas 《European journal of applied physiology and occupational physiology》1989,58(6):563-567
Using a combination of single maximal stimuli and maximum voluntary contractions, a comparison has been made of muscle properties in pre- and post-pubertal male subjects. In the dorsiflexor and plantarflexor muscles of the ankle, the twitch and maximum voluntary torques were approximately twice as large in the older subjects; the mean height and mean weight increased by factors of 1.20 and 1.86 respectively. The only other muscle parameter that changed, as a function of age, was the contraction time of the ankle dorsiflexors; the mean value was significantly longer in the older subjects. In the younger subjects, there were already clear differences between the dorsiflexor and plantarflexor muscles, the former developing smaller torques and having shorter contraction and half-relaxation times, greater post-activation potentiation and more susceptibility to fatigue. Even in the youngest subject, motor unit activation was complete in the ankle dorsiflexors; although this was not always true of the plantarflexors, the difference between the two subject groups was not significant. 相似文献
784.
785.
786.
D. S. Ushakov 《Biophysics》2008,53(6):505-509
The review summarizes the recent data on the structure and function of the essential light chain of myosin. It is known that the essential light chain of myosin stabilizes the lever arm. Consistent with the model of the shift of the dynamic population of conformations, the conformational flexibility of the essential light chain is emphasized, which opens the way to determining its new functions. It is proposed that the interaction between the C-terminal domain of the essential light chain and the N-terminal subdomain of the heavy chain of myosin may be involved in the coupling of ATP hydrolysis and rotation of the lever arm. The recent data indicate that the isoforms of the essential light chain with the additional N-terminal peptide are capable of interacting with actin and src-homologous domain 3 of myosin. The structural aspects of these interactions and the modulatory role of the isoforms of the essential light chain of myosin are discussed. 相似文献
787.
The influence of agonist premotor silence and the stretch-shortening cycle on contractile rate in active skeletal muscle 总被引:1,自引:0,他引:1
Charles B. Walter 《European journal of applied physiology and occupational physiology》1988,57(5):577-582
Agonist premotor silence (PMS), a brief period of relative quiescence in active skeletal muscle prior to phasic activation, was investigated in subjects performing maximal contractions. The frequency of occurrence and potential function of the silent period were examined for elbow flexions and extensions. PMS was evident for movements in both directions, indicating that the mechanism is not primarily limited to extensors as previously hypothesized. Flexions demonstrating PMS exhibited increased velocity and acceleration; however, kinematic facilitation was only evident on trials exhibiting the muscular stretch-shortening cycle (SSC). The SSC was present on trials lacking PMS, demonstrating that biceps and triceps silence are not the sole determinants of preparatory agonist lengthening for elbow flexions and extensions, respectively. Taken together, the data indicate that agonist PMS is a mechanism under apparent central control that acts concomitantly with mechanical factors to potentiate elbow flexor contractions. 相似文献
788.
J. Celichowski K. Grottel E. Bichler 《European journal of applied physiology and occupational physiology》1998,78(4):283-288
In previous studies on mechanomyogram (MMG) signals no analysis of these signals accompanying force generation has been performed.
Therefore, we have recorded MMG signals (previously referred to as muscle sound or acoustomyographic signals) during voluntary
contractions of forefinger flexor muscles in 31 young subjects. These subjects made contractions to produce force records
of triangular or trapeziform shape. The peak target force amounted to 10, 20 or 40 N which represented less than 40% of maximal
voluntary contraction. The MMG signals during the transient phases of force generation at three different rates were analysed.
The MMG intensity level calculated for MMG records and the peak-to-peak amplitude of MMG signals correlated with both the
velocity of force increase and the contraction force. The occurrence of the strongest MMG signals corresponded to changes
in contractile force. Therefore, it is suggested that measurements of these parameters could be a useful tool in studies of
changes in contractile force.
Accepted: 11 March 1998 相似文献
789.
Intramuscular pressure and muscle blood flow in supraspinatus 总被引:2,自引:0,他引:2
Ulf J?rvholm Jorma Styf Madis Suurkula Peter Herberts 《European journal of applied physiology and occupational physiology》1988,58(3):219-224
Intramuscular pressure and muscle blood flow was measured in the supraspinatus muscle in 6 healthy subjects. The recordings were performed at rest, during isometric exercise, during an isometric muscle contraction of 5.6 kPa (42 mm Hg) and 10.4 kPa (78 mm Hg) and at rest after the contraction. Intramuscular pressure was measured by the microcapillary infusion technique, and muscle blood flow by the Xenon-133 washout technique. Intramuscular pressure was 38.2 kPa (SD 12.0) (287 mm Hg) during maximal voluntary contraction. A muscle contraction pressure of 5.6 kPa (42 mm Hg), which is 16% of maximal voluntary contraction, reduces local muscle blood flow significantly. It is concluded that the high intramuscular pressures found in supraspinatus during work with the arms elevated impedes local muscle blood flow. 相似文献
790.
The reproducibility of test contractions for calibration of electromyographic measurements 总被引:1,自引:0,他引:1
K. B. Veiersted 《European journal of applied physiology and occupational physiology》1991,62(2):91-98
The main purpose of this study was to evaluate the reproducibility of electromyographic (EMG) measurements and specifically to test a calibration procedure with submaximal test contractions. Bipolar surface electrodes (20 mm fixed distance) were repositioned by a tracing sheet on both trapezius muscles, halfway between acromion and processus prominens. Submaximal test contractions were performed by keeping both arms straight abducted 90 degrees and forward flexed 10 degrees for 15-s periods. The arm position could be precisely reproduced in the frontal plane, but deviated forwards by 4 degrees in the horizontal plane, where the sensitivity of the EMG response to arm position was lowest. The electrodes were repositioned within a radius of 3 mm with a probability of 90%. Large deviations in the EMG response were found within this radius and a significant depression of the EMG response was recorded over the middle part of the muscle (the innervation zone?). This change in sensitivity of the EMG response with electrode position occurred in parallel for the test and maximal contractions. The total coefficient of variation was estimated to be 23% for recurrent EMG measurements using the calibration procedure described. 相似文献