Posttetanic potentiation and skeletal muscle fatigue: interactions with caffeine

1987 ◽  
Vol 65 (2) ◽  
pp. 260-268 ◽  
Author(s):  
Brian R. MacIntosh ◽  
Philip F. Gardiner
Keyword(s):  
Gastrocnemius Muscle ◽  
Additive Group ◽  
Repetitive Stimulation ◽  
Posttetanic Potentiation ◽  
Contraction Time ◽  
Twitch Response ◽  
Fatigued Muscle ◽  
Proportional Change ◽  
Before And After

The purpose of this study was to determine the interaction of three factors that modify twitch contraction amplitude in the rat gastrocnemius muscle in situ: posttetanic potentiation, fatigue, and caffeine. Posttetanic (200 Hz for 1 s) twitch responses were observed before and after 15 Hz stimulation for 6 min (group FS), injection of caffeine (75 mg/kg dissolved in saline, gropu NC), a combination of both repetitive stimulation and caffeine injection (group FC), or no treatment (group NS). Developed tension increased significantly with posttetanic potentiation and caffeine injection and these potentiating factors were additive (group NC). Repetitive stimulation attenuated the twitch response and the fatigued muscle was still responsive to the potentiating factors. Posttetanic potentiation was accomplished primarily by a significant increase in the peak rate of force development whereas caffeine potentiation and fatigue were effected with a proportional change in contraction time. It seems likely that the mechanism of posttetanic potentiation is not the same as the mechanism of caffeine-induced potentiation. Caffeine-induced potentiation is known to be related to increased release of calcium. Because changes in contraction time with fatigue were opposite to those associated with caffeine potentiation, it is proposed that the attenuated twitch response in fatigue results from reduced release of calcium.

Length dependence of staircase potentiation: interactions with caffeine and dantrolene sodium

2000 ◽  
Vol 78 (4) ◽  
pp. 350-357 ◽  
Author(s):  
Dilson E Rassier ◽  
Brian R MacIntosh
Keyword(s):  
Skeletal Muscle ◽  
Gastrocnemius Muscle ◽  
Repetitive Stimulation ◽  
Mammalian Skeletal Muscle ◽  
Optimal Length ◽  
Dantrolene Sodium ◽  
Length Dependence ◽  
Before And After ◽  
Isometric Twitch

In skeletal muscle, there is a length dependence of staircase potentiation for which the mechanism is unclear. In this study we tested the hypothesis that abolition of this length dependence by caffeine is effected by a mechanism independent of enhanced Ca2+ release. To test this hypothesis we have used caffeine, which abolishes length dependence of potentiation, and dantrolene sodium, which inhibits Ca2+ release. In situ isometric twitch contractions of rat gastrocnemius muscle before and after 20 s of repetitive stimulation at 5 Hz were analyzed at optimal length (Lo), Lo - 10%, and Lo + 10%. Potentiation was observed to be length dependent, with an increase in developed tension (DT) of 78 ± 12, 51 ± 5, and 34 ± 9% (mean ± SEM), at Lo - 10%, Lo, and Lo + 10%, respectively. Caffeine diminished the length dependence of activation and suppressed the length dependence of staircase potentiation, giving increases in DT of 65±13, 53 ± 11, and 45 ± 12% for Lo - 10%, Lo, and Lo + 10%, respectively. Dantrolene administered after caffeine did not reverse this effect. Dantrolene alone depressed the potentiation response, but did not affect the length dependence of staircase potentiation, with increases in DT of 58 ± 17, 26 ± 8, and 18 ± 7%, respectively. This study confirms that there is a length dependence of staircase potentiation in mammalian skeletal muscle which is suppressed by caffeine. Since dantrolene did not alter this suppression of the length dependence of potentiation by caffeine, it is apparently not directly modulated by Ca2+ availability in the myoplasm.

Absence of staircase following disuse in rat gastrocnemius muscle

1988 ◽  
Vol 66 (6) ◽  
pp. 707-713 ◽  
Author(s):  
Brian R. MacIntosh ◽  
Marie-Cristine Roberge ◽  
Phillip F. Gardiner
Keyword(s):  
Skeletal Muscles ◽  
Time Course ◽  
Gastrocnemius Muscle ◽  
Repetitive Stimulation ◽  
Muscle Weight ◽  
Twitch Contraction ◽  
Fast Twitch ◽  
Pulse Stimulation ◽  
Stimulation Of

Repetitive stimulation of mammalian fast-twitch skeletal muscles will normally result in a positive staircase response. This phenomenon was investigated in the rat gastrocnemius muscle following a 2-week period of tetrodotoxin-induced disuse. Muscle inactivity was imposed by superfusing tetrodotoxin in saline over the left sciatic nerve via an implanted osmotic pump. In situ isometric contractile responses to double pulse stimulation and repetitive stimulation at 10 Hz were determined the day after removal of the pump. Two weeks of disuse resulted in 40% muscle weight loss. A twitch contraction gave the same force when expressed per gram of wet muscle weight in control muscles, 317 ± 24.6 [Formula: see text] g/g, as compared with tetrodotoxin-treated muscles, 328 ± 24.2 g/g. Both contraction time and half-relaxation time were prolonged following treatment with tetrodotoxin. Repetitive stimulation at 10 Hz resulted in a positive staircase response in the control muscles, but not in muscles of the tetrodotoxin-treated rats. The observed changes in the time course of the twitch contraction with repetitive stimulation following tetrodotoxin-induced disuse are consistent with alterations in sarcoplasmic reticulum handling of calcium. It is not certain if there is a change following disuse in the mechanism normally associated with staircase or if this mechanism is merely opposed by an early fatigue.

Length-dependent potentiation and myosin light chain phosphorylation in rat gastrocnemius muscle

1997 ◽  
Vol 273 (1) ◽  
pp. C198-C204 ◽  
Author(s):  
D. E. Rassier ◽  
L. A. Tubman ◽  
B. R. MacIntosh
Keyword(s):  
Skeletal Muscle ◽  
Gastrocnemius Muscle ◽  
Average Rate ◽  
Muscle Length ◽  
Repetitive Stimulation ◽  
Mammalian Skeletal Muscle ◽  
Optimal Length ◽  
Regulatory Light Chains ◽  
Dependent Change

Changes in muscle length affect the degree of staircase potentiation in skeletal muscle, but the mechanism by which this occurs is unknown. In this study, we tested the hypothesis that length-dependent change in staircase is modulated by phosphorylation of the myosin regulatory light chains (RLC), since this is believed to be the main mechanism of potentiation. In situ isometric contractile responses of rat gastrocnemius muscle during 10 s of repetitive stimulation at 10 Hz were analyzed at optimal length (Lo), Lo - 10%, and Lo + 10%. The degree of enhancement of developed tension during 10 s of repetitive stimulation was observed to be length dependent, with increases of 118.5 +/- 7.8, 63.1 +/- 3.9, and 45.6 +/- 4.1% (means +/- SE) at Lo - 10%, Lo, and Lo + 10%, respectively. Staircase was accompanied by increases in the average rate of force development of 105.6 +/- 7.7, 55.6 +/- 4.1, and 37.2 +/- 4.4% for Lo - 10%, Lo, and Lo + 10%, respectively. RLC phosphorylation after 10 s of 10-Hz stimulation was higher than under resting conditions but not different among Lo - 10% (40 +/- 3.5%), Lo (35 +/- 3.5%), and Lo + 10% (41 +/- 3.5%). This study shows that there is a length dependence of staircase potentiation in mammalian skeletal muscle that may not be directly modulated by RLC phosphorylation. Interaction of RLC phosphorylation with length-dependent changes in Ca2+ release and intermyofilament spacing may explain these observations.

Increased V˙o 2 maxwith right-shifted Hb-O2dissociation curve at a constant O2 delivery in dog muscle in situ

1998 ◽  
Vol 84 (3) ◽  
pp. 995-1002 ◽  
Author(s):  
Russell S. Richardson ◽  
Kuldeep Tagore ◽  
Luke J. Haseler ◽  
Maria Jordan ◽  
Peter D. Wagner
Keyword(s):  
Gastrocnemius Muscle ◽  
Maximal Exercise ◽  
Diffusive Transport ◽  
Dissociation Curve ◽  
Before And After ◽  
Methylpropionic Acid ◽  
The Right ◽  
O2 Delivery ◽  
Diffusive Component

If the diffusive component of O2 transport in muscle is important in determining exercise capacity, an increased capillary-to-tissue [Formula: see text] difference should enhance gas exchange from blood to skeletal muscle during exercise. Thus a rightward shift in the O2 dissociation curve should theoretically increase O2extraction and improve maximal O2uptake (V˙o 2 max). To test this hypothesis, we used the canine gastrocnemius muscle to study maximal exercise in eight dogs at a normal P50 (33.1 ± 0.4 Torr) and with the O2 dissociation curve shifted to the right by an allosteric modifier of hemoglobin (Hb) (methylpropionic acid, RSR-13; P50 = 53.2 ± 5.0 Torr). Four control dogs were also studied before and after infusion of vehicle. O2 (100%) was inspired during exercise to maintain arterial saturation in both conditions. The muscle was surgically isolated and electrically stimulated (tetanic train: 0.2-ms stimuli for 200-ms duration at 50 Hz, once per s). To maintain O2 delivery (pre-RSR-13 = 19.1 ± 2.9; RSR-13 = 19.6 ± 2.5 ml ⋅ 100 g−1 ⋅ min−1), the muscle was pump perfused. At a constant O2 delivery, RSR-13 significantly increased percent O2 extraction (pre-RSR-13 = 61 ± 4.0; RSR-13 = 75.5 ± 4.7) and muscle V˙o 2 max(pre-RSR-13 = 11.8 ± 2.1; RSR-13 = 14.2 ± 1.5 ml ⋅ 100 g−1 ⋅ min−1). This improvement inV˙o 2 max with increased P50 demonstrates its O2 supply dependence when P50 is normal and the importance of O2 diffusive transport to muscle at maximal exercise.

The influence of osteopathic correction on the viscoelastic characteristics of the lower leg muscles

2019 ◽  
pp. 93-98
Author(s):  
E. M. Timanin ◽  
N. S. Sydneva ◽  
A. A. Zakharova
Keyword(s):  
Viscoelastic Properties ◽  
Gastrocnemius Muscle ◽  
Soft Tissues ◽  
Subjective Assessment ◽  
Lymphatic Drainage ◽  
Intercellular Substance ◽  
Leg Muscles ◽  
Before And After ◽  
Viscoelastic Characteristics ◽  
Instrumental Methods

Introduction. To date there is a lack of studies dedicated to the objectification of the palpation data obtained by a specialist during the osteopathic examination. The issue of the evidence of the results of osteopathic correction still remains important. Search for instrumental methods allowing to register and to measure various palpation phenomena and manifestations of somatic dysfunctions is very relevant for the development of osteopathy as a science. It is also very important to find objective characteristics of these methods.Goal of research — to study viscoelastic characteristics of the soft tissues of the lower legs by palpation and instrumental methods before and after osteopathic correction.Materials and methods. 22 volunteers (12 women and 10 men) aged 18–23 years without complaints of the musculoskeletal system were examined. Osteopathic diagnostics and measurement of the viscoelastic properties of muscles were carried out by the method of vibration viscoelastometry before and after osteopathic correction.Results. Correlation analysis by Spearman showed that the subjective assessment of an osteopath positively correlated with both elasticity (r=0,43, p<0,05) and viscosity of soft issues (r=0,29, p<0,05). For the gastrocnemius muscle, this pattern was even more pronounced — for elasticity r=0,51, p<0,05, for viscosity =0,34, p<0,05. After osteopathic correction no changes in the elasticity of the soft tissues were observed. The viscosity of the tissues reduced, but in the projection of the gastrocnemius muscle, these changes were not statistically significant (p=0,12), whereas in the projection of the soleus muscle statistically significant changes (p=0,034) were observed.Conclusion. Changes in the viscoelastic properties of tissues demonstrated that the effects of osteopathic correction with the use of myofascial mobilization techniques, articulation mobilization techniques, and lymphatic drainage techniques were not obvious. The elasticity of soft tissues of the lower legs did not change, while the viscosity decreased, especially in the projection of the soleus muscles. This effect of the osteopathic correction can be associated with the effect of thixotropy — the transformation of gel-like intercellular substance into sol. Thus, the research showed that vibration viscoelastometry can be used for the objectifi cation of the condition of soft tissues and of the effects of osteopathic correction.

Real-life Field Studies of the NOx Removing Properties of Photocatalytic Surfaces in Roskilde and Copenhagen Airport, Denmark

2020 ◽  
Vol 01 ◽  
Author(s):  
Henrik Jensen ◽  
Pernille D. Pedersen
Keyword(s):  
Air Quality ◽  
High Stability ◽  
Reference Site ◽  
Real Life ◽  
Field Studies ◽  
The Real ◽  
Before And After ◽  
Parking Lot ◽  
Photocatalytic Concrete

Aims: To evaluate the real-life effect of photocatalytic surfaces on the air quality at two test-sites in Denmark. Background: Poor air quality is today one of the largest environmental issues, due to the adverse effects on human health associated with high levels of air pollution, including respiratory issues, cardiovascular disease (CVD), and lung cancer. NOx removal by TiO2 based photocatalysis is a tool to improve air quality locally in areas where people are exposed. Methods: Two test sites were constructed in Roskilde and Copenhage airport. In Roskilde, the existing asphalt at two parking lots was treated with TiO2 containing liquid and an in-situ ISO 22197-1 test setup was developed to enable in-situ evaluation of the activity of the asphalt. In CPH airport, photocatalytic concrete tiles were installed at the "kiss and fly" parking lot, and NOx levels were continuously monitored in 0.5 m by CLD at the active site and a comparable reference site before and after installation for a period of 2 years. Results: The Roskilde showed high stability of the photocatalytic coating with the activity being largely unchanged over a period of 2 years. The CPH airport study showed that the average NOx levels were decreased by 12 % comparing the before and after NOx concentrations at the active and reference site. Conclusion: The joined results of the two Danish demonstration projects illustrate a high stability of the photocatalytic coating as well as a high potential for improvements of the real-life air quality in polluted areas.

scholarly journals Nanocomposites of Polyaniline and Cellulose Nanocrystals Prepared in Lyotropic Chiral Nematic Liquid Crystals

2013 ◽  
Vol 2013 ◽  
pp. 1-6 ◽  
Author(s):  
Dawei Zhang ◽  
Lihong Zhang ◽  
Bingzhe Wang ◽  
Guangzhe Piao
Keyword(s):  
Liquid Crystals ◽  
Cellulose Nanocrystals ◽  
Nematic Liquid Crystals ◽  
Weight Ratio ◽  
Asymmetric Reaction ◽  
Reaction Field ◽  
Electron Microscopies ◽  
Chiral Nematic ◽  
Before And After

Stable lyotropic chiral nematic liquid crystals (N*-LCs) of cellulose nanocrystals (CNs) were prepared via hydrolysis using sulfuric acid. The lyotropic N*-LCs were used as an asymmetric reaction field to synthesize polyaniline (PANI) onto CNs by in situ polymerization. As a primary step, we examined the mesophase transition of the N*-LCs of CNs suspension before and after in situ polymerization of aniline (ANI) by polarizing optical microscopy. The structure of nanocomposites of PANI/CNs was investigated at a microscopic level using Fourier transform infrared spectroscopy and X-ray diffraction. Influence of the CNs-to-ANI ratio on the morphology of the nanocomposites was also investigated at macroscopic level by scanning electron and transmission electron microscopies. It is found that the weight ratio of CNs to aniline in the suspension significantly influenced the size of the PANI particles and interaction between CNs and PANI. Moreover, electrical properties of the obtained PANI/CNs films were studied using standard four-probe technique. It is expected that the lyotropic N*-LCs of CNs might be available for an asymmetric reaction field to produce novel composites of conjugated materials.

In-Situ SEM Observations of Moving Interfaces during Recrystallisation

2006 ◽  
Vol 519-521 ◽  
pp. 1341-1348 ◽  
Author(s):  
Sybrand van der Zwaag ◽  
E. Anselmino ◽  
A. Miroux ◽  
David J. Prior
Keyword(s):  
Grain Boundaries ◽  
Small Groups ◽  
Detailed Understanding ◽  
Small Areas ◽  
Orientation Contrast ◽  
Moving Interfaces ◽  
Innovative Method ◽  
Before And After ◽  
In Situ Observations

To obtain further progress and a more detailed understanding of the mechanisms involved in recrystallisation, new and more accurate techniques such as in-situ observations are necessary. This innovative method has been used to monitor the recrystallisation process in a FEGSEM equipped with hot stage. Observations are done in backscatter mode with particular attention to orientation contrast. EBSD maps of the observed areas can be acquired before and after recrystallisation. Details of the movement of the interfaces between the recrystallised region and the parent structure are recorded and analysed. The results show that the grain boundaries observed do not move smoothly but with a jerky motion. The recrystallising front sweeps through small areas, corresponding to single sub-grains or small groups of them, very rapidly and then stops at other sub-grain boundaries for varying time before progressing to the following area.

Structural basis of muscle O2 diffusing capacity: evidence from muscle function in situ

2000 ◽  
Vol 88 (2) ◽  
pp. 560-566 ◽  
Author(s):  
Russell T. Hepple ◽  
Michael C. Hogan ◽  
Creed Stary ◽  
Donald E. Bebout ◽  
Odile Mathieu-Costello ◽  
...  
Keyword(s):  
Gastrocnemius Muscle ◽  
Capillary Density ◽  
Structural Basis ◽  
Diffusing Capacity ◽  
Diffusion Distance ◽  
Short Term ◽  
Cross Sectional ◽  
Intact Organism ◽  
Minimal Reduction

Although evidence for muscle O2 diffusion limitation of maximal O2 uptake has been found in the intact organism and isolated muscle, its relationship to diffusion distance has not been examined. Thus we studied six sets of three purpose-bred littermate dogs (aged 10–12 mo), with 1 dog per litter allocated to each of three groups: control (C), exercise trained for 8 wk (T), or left leg immobilized for 3 wk (I). The left gastrocnemius muscle from each animal was surgically isolated, pump-perfused, and electrically stimulated to peak O2 uptake at three randomly applied levels of arterial oxygenation [normoxia, arterial[Formula: see text]([Formula: see text]) 77 ± 2 (SE) Torr; moderate hypoxia, [Formula: see text]: 33 ± 1 Torr; and severe hypoxia, [Formula: see text]: 22 ± 1 Torr]. O2 delivery (ml ⋅ min−1 ⋅ 100 g− 1) was kept constant among groups for each level of oxygenation, with O2 delivery decreasing with decreasing [Formula: see text]. O2extraction (%) was lower in I than T or C for each condition, but calculated muscle O2 diffusing capacity (Dm[Formula: see text]) per 100 grams of muscle was not different among groups. After the experiment, the muscle was perfusion fixed in situ, and a sample from the midbelly was processed for microscopy. Immobilized muscle showed a 45% reduction of muscle fiber cross-sectional area ( P < 0.05), and a resulting 59% increase in capillary density ( P < 0.05) but minimal reduction in capillary-to-fiber ratio (not significant). In contrast, capillarity was not significantly different in T vs. C muscle. The results show that a dramatically increased capillary density (and reduced diffusion distance) after short-term immobilization does not improve Dm[Formula: see text] in heavily working skeletal muscle.

scholarly journals In Situ Coherent X-ray Diffraction during Three-Point Bending of a Au Nanowire: Visualization and Quantification

2018 ◽  
Vol 2 (4) ◽  
pp. 24 ◽  
Author(s):  
Anton Davydok ◽  
Thomas Cornelius ◽  
Zhe Ren ◽  
Cedric Leclere ◽  
Gilbert Chahine ◽  
...  
Keyword(s):  
Three Dimensional ◽  
Reciprocal Space ◽  
X Ray Diffraction ◽  
Complex Deformation ◽  
X Ray ◽  
Three Point Bending ◽  
Atomic Force ◽  
Au Nanowire ◽  
Before And After

The three-point bending behavior of a single Au nanowire deformed by an atomic force microscope was monitored by coherent X-ray diffraction using a sub-micrometer sized hard X-ray beam. Three-dimensional reciprocal-space maps were recorded before and after deformation by standard rocking curves and were measured by scanning the energy of the incident X-ray beam during deformation at different loading stages. The mechanical behavior of the nanowire was visualized in reciprocal space and a complex deformation mechanism is described. In addition to the expected bending of the nanowire, torsion was detected. Bending and torsion angles were quantified from the high-resolution diffraction data.

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