甲状腺功能亢进大鼠比目鱼肌肌浆网Ca2+-ATP酶活性增高可加速强直收缩疲劳

甲状腺功能亢进(甲亢)时甲状腺素分泌增加,不仅使具有神经支配的慢缩型肌纤维向快缩型转化,而且改变骨骼肌的强直收缩功能.因此,甲亢性肌病的肌肉乏力可能与骨骼肌强直收缩易发生疲劳有关.本实验在离体条件下,观测甲亢4周引起的大鼠慢缩肌--比目鱼肌(soleus, SOL)单收缩与间断强直收缩功能的变化.结果显示,甲亢4周大鼠体重明显低于同步对照组[(292±13)g vs (354±10)g],但SOL湿重没有明显改变[(107.3±8.6)mg vs (115.1±6.9)mg].甲亢大鼠SOL单收缩张力达到峰值的时间(time to peak tension, TPT)、从峰值降至75%舒张时间(time from peak tension to 75% relaxation, TR75)均明显缩短;强直收缩的TR75也明显缩短[(102.8±4.1)ms vs (178.8±15.8)ms];强直收缩的最适频率从对照组的100Hz增加到140Hz;间断强直收缩期间容易发生疲劳.甲亢大鼠SOL肌浆网Ca2 -ATP酶(sarcoplasmic-reticulum Ca2 -ATPase, SERCA)活性增高.采用SERCA特异性抑制剂CPA (1.0μmol/L)处理后,对照组与甲亢大鼠SOL间断强直收缩的TR75均延长,同时不易出现疲劳.5.0μmol/L CPA灌流虽可进一步抵抗甲亢大鼠SOL间断强直收缩引起的疲劳,但强直收缩期间的静息张力却明显升高.将CPA浓度增至10.0μmol/L,甲亢大鼠SOL间断强直收缩又趋向易发生疲劳.这些结果提示,与心肌相同,骨骼肌肌纤维SERCA活性亦可影响单收缩与强直收缩的舒张时间,SERCA活性升高可加速间断强直收缩发生疲劳.     

Sprint training attenuates the deficits of force and dynamic stiffness in rat soleus muscle caused by eccentric contractions

We investigated whether sprint training attenuates the deficits in force and dynamic stiffness caused by eccentric contractions to the soleus muscles of Wistar rats. Two groups of male rats were analyzed: sedentary (C, n=8) and trained (T, n=8). T rats were sprint trained for 10 weeks. Subsequently, the right soleus muscles of rats were freed under anesthesia, leaving the bone insertion and blood supply intact. Eccentric contractions were induced by lengthening muscles during tetanic contractions. Force and dynamic stiffness were tested before and after 20 rounds of eccentric contractions. Tension decline was analyzed using a two-state model (first-order kinetics) in the context of Kramer's theory. Training improved the twitch tension (C, 6.44+/-0.6N/cm(2); T, 10.90+/-0.8N/cm(2)), tetanic force (C, 61.74+/-0.6N/cm(2); T, 85.62+/-0.8N/cm(2)), and increased the dynamic stiffness (C, 41.28+/-1.0N/cm(2); T, 49.56+/-3.2N/cm(2)). Twitch tension after eccentric contractions declined to 73% and 75% in C and T groups, respectively, while tetanic tension decreased to 60% and 36% in C and T groups, respectively. After eccentric contractions, dynamic stiffness decreases were smaller in T rats (from 49.56+/-3.2 to 36.09+/-2.1N/cm(2)) than in C rats (from 41.28+/-1.0 to 20.73+/-1.8N/cm(2)). Sprint training increased the dynamic stiffness and tetanic tension of the soleus muscle and protected against the attenuation induced by eccentric contractions. Finally, the two-state model provided evidence that the number of force-generating cross-bridges increases in trained muscle.     

萎缩比目鱼肌间断强直收缩疲劳后恢复速率的影响因素

为研究模拟失重大鼠萎缩比目鱼肌强直收缩疲劳后恢复速率的影响因素,采用尾部悬吊模拟失重大鼠模型及离体骨骼肌条灌流技术,观测其在不同收缩模式下疲劳后的恢复过程。正常大鼠离体比目鱼肌条实验显示,10s短时程（S10P）与300s长时程（L10P）强直收缩轻度疲劳[强直收缩最大张力（P0）下降10％]后,在20min恢复期末,均可恢复至疲劳前P0,且恢复程度不受疲劳持续时间的影响;轻度疲劳后,在灌流液中加入10μmol／L钌红抑制肌浆网Ca^2＋释放功能,恢复速率减慢,恢复程度最大仅至94％P0,然后呈下降趋势,提示轻度疲劳可能仅抑制肌原纤维功能。60s短时程（S50P）与300s长时程（L50P）强直收缩中度疲劳（P0下降50％）后,在20min恢复期末,收缩张力分别恢复至95％P0和90％P0,表明中度疲劳持续时间影响恢复的速率;相同条件中度疲劳后,在灌流液中加入5mmol／L咖啡因促进肌浆网Ca62＋释放功能,恢复速率明显加快,无论疲劳持续时间长短,5min便可完全恢复,提示中度疲劳不仅抑制肌原纤维功能,还抑制肌浆网Ca^2＋释放功能。尾部悬吊1周的大鼠比目鱼肌明显萎缩,其重量／体重之比仅为对照大鼠的60％。采用短与长持续时间的轻与中度疲劳作用后,在20min恢复期末,收缩张力分别恢复至94％P0（S10P）、95％P0（L10P）、92％P0（S50P）、84％P0（L50P）,均与同步对照组有显著差异。以上结果提示：模拟失重1周大鼠萎缩的比目鱼肌,轻度与中度疲劳均可抑制肌原纤维功能与肌浆网Ca^2＋释放功能,使恢复速率减慢。     

Differences between VO2 maxima of twitch and tetanic contractions are related to blood flow

The purpose of this investigation was to compare oxygen uptake (VO2) and fatigue characteristics of isotonic tetanic contractions with those observed during isotonic twitches in dog gastrocnemius-plantaris muscle. Tetanic contractions (1/s, 200-ms trains of 50 impulses/s) elicited a peak VO2 of 9.01 +/- 0.42 mumol.g-1.min-1, which declined 29% in 30 min. The peak was significantly lower during 4/s twitches (6.23 +/- 0.36 mumol.g-1.min-1), but the rate of decline was similar. Peak blood flow (Q) was 37% higher and decreased more slowly during tetanic than twitch contractions. VO2/Q and VO2/venous PO2 were similar in both groups at peak VO2 and later declined or remained constant over time. Power was significantly greater with tetanic contractions with the relative decline between 3 and 30 min similar in both groups (32 and 37%). In conclusion, tetanic contractions result in significantly higher VO2 and power than do twitch contractions. This was derived primarily from increased Q because the arteriovenous O2 difference was similar. A significant determinant of the difference in Q between twitch and tetanic contractions is mechanical hindrance of Q. There is relatively more time for unhindered flow in the tetanic contractions. In electrically stimulated muscles, maximal VO2 is related to Q and reflects mainly Q through the muscle rather than the VO2 capacity of the muscle.     

Elevated muscle vitamin E does not attenuate eccentric exercise-induced muscle injury.

The purpose of this study was to evaluate the effect of elevated muscle vitamin E content on skeletal muscle damage from eccentric exercise. Sixty Sprague-Dawley rats were put on a normal (40 IU vitamin E/kg food) or supplemented (10,000 IU vitamin E/kg food) diet for 5 wk. Injury in soleus muscle was determined using several criteria: reductions in maximal tetanic force and number of intact fibers per square millimeter and elevations in muscle glucose 6-phosphate dehydrogenase activity and plasma creatine kinase activity, either immediately (0 h) or 2 days (48 h) after a downhill walking protocol. Sedentary animals were also tested but did not exercise. Muscle vitamin E levels were significantly elevated (approximately 3- to 4-fold), and susceptibility of the muscles to oxidant stress was decreased, after supplementation. However, vitamin E supplementation did not attenuate injury by any of the criteria employed. Maximal tetanic force decreased approximately 20% at 0 and 48 h after exercise in both groups. The number of intact fibers per square millimeter decreased approximately 30-35% in both groups at 0 and 48 h. Glucose 6-phosphate dehydrogenase activity increased approximately 50-100% in both groups at 48 h, and plasma creatine kinase activity was elevated approximately 2- to 2.5-fold at 0 h in both groups. These findings do not support a major role for free radical damage to muscle membranes in the initiation of injury from eccentric exercise, although they do not disprove free radical involvement in the etiology.     

Low-level laser therapy attenuates the acute inflammatory response induced by muscle traumatic injury

The purpose of this work was to investigate the effect of early and long-term low-level laser therapy (LLLT) on oxidative stress and inflammatory biomarkers after acute-traumatic muscle injury in Wistar rats. Animals were randomly divided into the following four groups: control group (CG), muscle injury group (IG), CG?+?LLLT, and IG?+?LLLT: laser treatment with doses of 3 and 5 J/cm². Muscle traumatic injury was induced by a single-impact blunt trauma in the rat gastrocnemius. Irradiation for 3 or 5 J/cm² was initiated 2, 12, and 24?h after muscle trauma induction, and the treatment was continued for five consecutive days. All the oxidant markers investigated. namely thiobarbituric acid-reactive substance, carbonyl, superoxide dismutase, glutathione peroxidase, and catalase, were increased as soon as 2?h after muscle injury and remained increased up to 24?h. These alterations were prevented by LLLT at a 3 J/cm² dose given 2?h after the trauma. Similarly, LLLT prevented the trauma-induced proinflammatory state characterized by IL-6 and IL-10. In parallel, trauma-induced reduction in BDNF and VEGF, vascular remodeling and fiber-proliferating markers, was prevented by laser irradiation. In order to test whether the preventive effect of LLLT was also reflected in muscle functionality, we tested the locomotor activity, by measuring distance traveled and the number of rearings in the open field test. LLLT was effective in recovering the normal locomotion, indicating that the irradiation induced biostimulatory effects that accelerated or resolved the acute inflammatory response as well as the oxidant state elicited by the muscle trauma.     

Attenuation of force deficit after lengthening contractions in soleus muscle from trained rats.

The purposes of this study were 1) to determine the extent to which endurance training reduces the functional deficit induced by lengthening contractions in the soleus (Sol) muscle and 2) to determine whether young and old rats training at a comparable relative exercise intensity would demonstrate a similar protective effect from lengthening-contraction-induced injury. Young (3-mo-old) and old (23-mo-old) male Fischer 344 rats were randomly assigned to either a control or exercise training group [young control (YC), old control (OC), young trained (YT), old trained (OT)]. Exercise training consisted of 10 wk of treadmill running (15% grade, 45 min/day, and 5 days/wk) such that by the end of training the young and old rats were exercising at 27 and 15 m/min, respectively. After training, contractile properties of the Sol muscle were measured in vitro at 26 degrees C. The percent decrease in maximal isometric specific force (P(o)) was determined after a series of 20 lengthening contractions (20% strain from optimal muscle length, 1 contraction every 5 s). After the lengthening-contraction protocol, Sol muscle P(o) was decreased by approximately 26% (19.6 vs. 14.6 N/cm(2)) and 28% (14.8 vs. 9.6 N/cm(2)) in the YC and OC rats, respectively. After exercise training, the reduction in P(o) was significantly (P < 0.05) attenuated to a similar degree ( approximately 13%) in both YT rats (18.7 vs. 16.2 N/cm(2)) and OT rats (15.8 vs. 13.7 N/cm(2)). It is concluded that exercise training attenuates the force deficit after repeated lengthening contractions to a comparable extent in young and old rats training at a similar exercise intensity.     

Red and Infrared Low-Level Laser Therapy Prior to Injury with or without Administration after Injury Modulate Oxidative Stress during the Muscle Repair Process

IntroductionMuscle injury is common among athletes and amateur practitioners of sports. Following an injury, the production of reactive oxygen species (ROS) occurs, which can harm healthy muscle fibers (secondary damage) and delay the repair process. Low-level laser therapy (LLLT) administered prior to or following an injury has demonstrated positive and protective effects on muscle repair, but the combination of both administration times together has not been clarified.AimTo evaluate the effect of LLLT (660 nm and 780 nm, 10 J/cm², 40 mW, 3.2 J) prior to injury with or without the administration after injury on oxidative stress during the muscle repair process.MethodsWistar rats were divided into following groups: control; muscle injury alone; LLLT 660 nm + injury; LLLT 780 nm + injury; LLLT 660 nm before and after injury; and LLLT 780 nm before and after injury. The rats were euthanized on days 1, 3 and 7 following cryoinjury of the tibialis anterior (TA) muscle, which was then removed for analysis.ResultsLipid peroxidation decreased in the 660+injury group after one day. Moreover, red and infrared LLLT employed at both administration times induced a decrease in lipid peroxidation after seven days. CAT activity was altered by LLLT in all periods evaluated, with a decrease after one day in the 780+injury+780 group and after seven days in the 780+injury group as well as an increase in the 780+injury and 780+injury+780 groups after three days. Furthermore, increases in GPx and SOD activity were found after seven days in the 780+injury+780 group.ConclusionThe administration of red and infrared laser therapy at different times positively modulates the activity of antioxidant enzymes and reduces stress markers during the muscle repair process.     

Influence of nitric oxide on vascular resistance and muscle mechanics during tetanic contractions in situ.

Studies of the effect of nitric oxide (NO) synthesis inhibition were performed in the isometrically contracting blood-perfused canine gastrocnemius-plantaris muscle group. Muscle blood flow (Q) was controlled with a pump during continuous NO blockade produced with either 1 mM L-argininosuccinic acid (L-ArgSA) or N(G)-nitro-L-arginine methyl ester (L-NAME) during repetitive tetanic contractions (50-Hz trains, 200-ms duration, 1/s). Pump Q was set to match maximal spontaneous Q (1.3-1.4 ml. min(-1). g(-1)) measured in prior, brief (3-5 min) control contraction trials in each muscle. Active tension and oxygen uptake were 500-600 g/g and 200-230 microl. min(-1). g(-1), respectively, under these conditions. Within 3 min of L-ArgSA infusion, vascular resistance across the muscle (R(v)) increased significantly (from approximately 100 to 300 peripheral resistance units; P < 0.05), whereas R(v) increased to a lesser extent with L-NAME (from approximately 100 to 175 peripheral resistance units; P < 0.05). The increase in R(v) with L-ArgSA was unchanged by simultaneous infusion of 0.5-10 mM L-arginine but was reduced with 1-3 microg/ml sodium nitroprusside (41-54%). The increase in R(v) with L-NAME was reversed with 1 mM of L-arginine. Increased fatigue occurred with infusion of L-ArgSA; active tension and intramuscular pressure decreased by 62 and 66%, whereas passive tension and baseline intramuscular pressure increased by 80 and 30%, respectively. These data indicate a possible role for NO in the control of R(v) and contractility within the canine gastrocnemius-plantaris muscle during repetitive tetanic contractions.     

Oxidation/reduction state of cytochrome oxidase during repetitive contractions

There is disagreement regarding whether inadequate O2 determines maximal O2 uptake (VO2max) and lactic acid output (L) during muscular activity. Direct assessment of mitochondrial cytochrome oxidase (cytochrome a-a3) oxidation/reduction (O/R) state should provide an unequivocal answer for this issue. A new near-infrared spectrophotometric method was used to measure the O/R state of cytochrome a-a3 of dog gastrocnemius-plantaris muscle in situ during repetitive isotonic twitch and tetanic contractions. Three contraction frequencies were used for each contraction type in alternating sequence to provide a wide range of VO2 up to VO2max. VO2 and L were measured after 3 and 9 min of a 10-min contraction period, and 15 min were allowed for recovery between contraction periods. VO2 increased with contraction frequency. L was variably increased with contraction frequency at 3 min and uptake usually occurred at 9 min, except at the highest tetanic frequency. The O/R span of cytochrome a-a3 was determined by respiring the animals with 100% N2 to determine the most reduced state. This was followed by respiration with 100% O2, which gave the most oxidized state transiently during recovery. Within this span in muscles at rest, cytochrome a-a3 was 50-80% oxidized. During contractions of both types at all frequencies, cytochrome a-a3 always became more oxidized by an additional 10-20%. These findings should put to rest any arguments that inadequate O2 is a determinant of VO2max or L under the conditions of these experiments: repetitive contractions with free flow in self-perfused muscles and normoxia.     

Muscle weakness following sustained and rhythmic isometric contractions in man

The effects of sustained and rhythmically performed isometric contractions on electrically evoked twitch and tetanic force generation of the triceps surae have been investigated in 4 healthy male subjects. The isometric contractions were performed separately and on different occasions at 30%, 60% and 100% of the force of maximal voluntary contraction (MVC). The area under the maximal voluntary contraction (MVC) force/time curve during the rhythmic and sustained contractions was the same for each experiment. The results showed that following rhythmic isometric exercise there was a small decrease in low (10 and 20 Hz) and high (40 Hz) frequency tetanic tension which was associated with % MVC. However, there was no change in the 20/40 ratio of tetanic forces, MVC or the contraction times and force of the maximal twitch. In contrast, following sustained isometric exercise tetanic forces were markedly reduced, particularly at low frequencies of stimulation. The 20/40 ratio decreased and the induced muscle weakness was greater at 30% than 60% or 100% MVC. The performance of sustained isometric contractions also effected a decrease in contraction time of the twitch and MVC. The results are in accord with previous findings for dynamic work (Davies and White 1982), and show that if isometric exercise is performed rhythmically the effect on tetanic tensions is small and there is no evidence of a preferential loss of electrically evoked force at either high or low frequencies of stimulation following the contractions. For sustained contractions, however, the opposite is true, the ratio of 20/40 Hz forces is markedly reduced and following 30% sustained MVC there is a significant (p less than 0.05) change in the time to peak tension (TPT) of the maximal twitch.     

Skeletal muscle relaxation rate after fasting or hypocaloric feeding

The effect of malnutrition on skeletal muscle relaxation is not entirely clear; some studies indicate no change and others a slowing of the relaxation rate. We investigated whether these different results were due to type of malnutrition, muscle fiber type composition, or the index used to express relaxation rate. The effect of a 2-day fast (16% body wt loss) or 1 wk of hypocaloric feeding (22.6% wt loss) on relaxation rates of soleus and extensor digitorum longus (EDL) muscles was studied in situ with the use of anesthetized adult Wistar rats. Relaxation rates were assessed for twitch contractions using half-relaxation times and exponential phase half-times and for tetanic contractions using exponential phase half-times. The rate of relaxation was unaffected by fasting, whereas hypocaloric feeding reduced relaxation rates after twitch and tetanic contractions in both soleus and EDL muscles. We conclude that slowing of skeletal muscle relaxation rate occurs after 1 wk of hypocaloric feeding but not after 2 days of fasting. The slowing is independent of muscle fiber composition, type of contraction, or the index used to express relaxation rate.     

Postactivation potentiation in a human muscle: effect on the load-velocity relation of tetanic and voluntary shortening contractions.

Recently it was demonstrated that postactivation potentiation (PAP), which refers to the enhancement of the muscle twitch torque as a result of a prior conditioning contraction, increased the maximal rate of torque development of tetanic and voluntary isometric contractions (3). In this study, we investigated the effects of PAP and its decay over time on the load-velocity relation. To that purpose, angular velocity of thumb adduction in response to a single electrical stimulus (twitch), a high-frequency train of 15 pulses at 250 Hz (HFT(250)), and during ballistic voluntary shortening contractions, performed against loads ranging from 10 to 50% of the maximum torque, were recorded before and after a conditioning 6-s maximal voluntary contraction (MVC). The results showed an increase of the peak angular velocity for the different loads tested after the conditioning MVC (P < 0.001), but the effect was greatest for the twitch ( approximately 182%) compared with the HFT(250) or voluntary contractions ( approximately 14% for both contraction types). The maximal potentiation occurred immediately following the conditioning MVC for the twitch, whereas it was reached 1 min later for the tetanic and ballistic voluntary contractions. At that time, the load-velocity relation was significantly shifted upward, and the maximal power of the muscle was increased ( approximately 13%; P < 0.001). Furthermore, the results also indicated that the effect of PAP on shortening contractions was not related to the modality of muscle activation. In conclusion, the findings suggest a functional significance of PAP in human movements by improving muscle performance of voluntary dynamic contractions.     

Effects of acute creatine kinase inhibition on metabolism and tension development in isolated single myocytes.

This study investigated the effects of acute creatine kinase (CK) inhibition (CKi) on contractile performance, cytosolic Ca2+ concentration ([Ca2+]c), and intracellular PO2 (PIO2) in Xenopus laevis isolated myocytes during a 2-min bout of isometric tetanic contractions (0.33-Hz frequency). Peak tension was similar between trials during the first contraction but was significantly (P < 0.05) attenuated for all subsequent contractions in CKi vs. control (Con). The fall in PIO2 (DeltaPIO2) from resting values was significantly greater in Con (26.0 +/- 2.2 Torr) compared with CKi (17.8 +/- 1.8 Torr). However, the ratios of Con to CKi end-peak tension (1.53 +/- 0.11) and DeltaPO2 (1.49 +/- 0.11) were similar, suggesting an unaltered aerobic cost of contractions. Additionally, the mean response time (MRT) of DeltaPIO2was significantly faster in CKi vs. Con during both the onset (31.8 +/- 5.5 vs. 49.3 +/- 5.7 s; P < 0.05) and cessation (21.2 +/- 4.1 vs. 68.0 +/- 3.2 s; P < 0.001) of contractions. These data demonstrate that initial phosphocreatine hydrolysis in single skeletal muscle fibers is crucial for maintenance of sarcoplasmic reticulum Ca2+ release and peak tension during a bout of repetitive tetanic contractions. Furthermore, as PIO2 fell more rapidly at contraction onset in CKi compared with Con, these data suggest that CK activity temporally buffers the initial ATP-to-ADP concentration ratio at the transition to an augmented energetic demand, thereby slowing the initial mitochondrial activation by mitigating the energetic control signal (i.e., ADP concentration, phosphorylation potential, etc.) between sites of ATP supply and demand.     

Force-velocity shifts with repetitive isometric and isotonic contractions of canine gastrocnemius in situ.

The force-velocity (F-V) relationships of canine gastrocnemius-plantaris muscles at optimal muscle length in situ were studied before and after 10 min of repetitive isometric or isotonic tetanic contractions induced by electrical stimulation of the sciatic nerve (200-ms trains, 50 impulses/s, 1 contraction/s). F-V relationships and maximal velocity of shortening (Vmax) were determined by curve fitting with the Hill equation. Mean Vmax before fatigue was 3.8 +/- 0.2 (SE) average fiber lengths/s; mean maximal isometric tension (Po) was 508 +/- 15 g/g. With a significant decrease of force development during isometric contractions (-27 +/- 4%, P < 0.01, n = 5), Vmax was unchanged. However, with repetitive isotonic contractions at a low load (P/Po = 0.25, n = 5), a significant decrease in Vmax was observed (-21 +/- 2%, P < 0.01), whereas Po was unchanged. Isotonic contractions at an intermediate load (P/Po = 0.5, n = 4) resulted in significant decreases in both Vmax (-26 +/- 6%, P < 0.05) and Po (-12 +/- 2%, P < 0.01). These results show that repeated contractions of canine skeletal muscle produce specific changes in the F-V relationship that are dependent on the type of contractions being performed and indicate that decreases in other contractile properties, such as velocity development and shortening, can occur independently of changes in isometric tension.     

810nm弱激光照射对大鼠急性脊髓损伤后巨噬细胞极化的作用研究

本研究构建急性大鼠脊髓夹伤模型,并将大鼠随机分为单纯脊髓损伤对照组及脊髓损伤联合弱激光照射组。照射组应用810 nm波长,150 m W照射功率,照射光斑0.3 cm^2的弱激光对脊髓损伤区进行经皮照射,连续照射3天,7天或14天。应用免疫荧光、免疫印迹实验方法,测定脊髓损伤区巨噬细胞及小胶质细胞的极化表达。应用酶联免疫吸附法测定脊髓损伤区白细胞介素4的表达情况。应用坚牢蓝髓鞘染色测定两组损伤脊髓中髓鞘保留的差异。采用BBB评分对两组大鼠后肢运动功能的恢复进行评估。结果表明,810 nm弱激光对脊髓损伤区连续照射3天,7天后,可显著减少M1型巨噬细胞及其标志物诱导型一氧化氮合酶的表达,在7天时间增加M2型巨噬细胞及其标志物精氨酸酶1的表达。弱激光照射组白细胞介素4的表达明显增加。损伤后14天,弱激光照射组脊髓损伤区髓鞘保留面积比值明显提高。损伤后7天及14天时,弱激光照射组大鼠的BBB评分明显升高。该实验结果表明,810 nm弱激光经皮照射,可增加大鼠急性脊髓损伤区M2型巨噬细胞及小胶质细胞的表达,并减少脊髓损伤后的髓鞘脱失,促进脊髓损伤大鼠运动功能的恢复。     

The effects of isotonic contractions on the rate of fatigue development and the resting membrane potential in the sartorius muscle of the frog, Rana pipiens.

The goal of this study was to characterize how isotonic contractions affect the rate of fatigue development. Muscle bundles dissected from frog sartorius muscles were stimulated with 100-ms long train of pulses (0.5 ms, 6 V, 140 Hz). To measure the effect of the isotonic contractions, isometric tetanus were elicited at regular time intervals during the stimulation to fatigue. In general, isotonic contractions caused a faster decrease in tetanic force than isometric contractions. The difference in tetanic force between an isotonic and isometric fatigue increased gradually over a 20-min period to 7.9 and 13.5% at 0.04 and 0.1 trains/s (TPS), respectively. At 0.2, 0.5, and 1.0 TPS, the decrease in tetanic force was also faster during an isotonic fatigue, which resulted in an initial difference in tetanic force between the two types of fatigue. The difference did not exceed 18.5% and did not persist throughout the stimulation period; i.e., the difference disappeared before the end of the fatigue stimulation. The half-relaxation time was prolonged during fatigue development, and the prolongation was greater during an isotonic fatigue, except at 0.04 TPS. The increases in the half-relaxation time at 0.2, 0.5, and 1.0 TPS were followed by a decrease, and the decreases were especially pronounced during an isotonic fatigue at 0.5 and 1.0 TPS. The results showed for the first time that isotonic contractions cause a faster rate of fatigue development in frog sartorius muscles, and this effect depends on the frequency of stimulation.     

Low-Level Laser Irradiation Improves Functional Recovery and Nerve Regeneration in Sciatic Nerve Crush Rat Injury Model

The development of noninvasive approaches to facilitate the regeneration of post-traumatic nerve injury is important for clinical rehabilitation. In this study, we investigated the effective dose of noninvasive 808-nm low-level laser therapy (LLLT) on sciatic nerve crush rat injury model. Thirty-six male Sprague Dawley rats were divided into 6 experimental groups: a normal group with or without 808-nm LLLT at 8 J/cm² and a sciatic nerve crush injury group with or without 808-nm LLLT at 3, 8 or 15 J/cm². Rats were given consecutive transcutaneous LLLT at the crush site and sacrificed 20 days after the crush injury. Functional assessments of nerve regeneration were analyzed using the sciatic functional index (SFI) and hindlimb range of motion (ROM). Nerve regeneration was investigated by measuring the myelin sheath thickness of the sciatic nerve using transmission electron microscopy (TEM) and by analyzing the expression of growth-associated protein 43 (GAP43) in sciatic nerve using western blot and immunofluorescence staining. We found that sciatic-injured rats that were irradiated with LLLT at both 3 and 8 J/cm² had significantly improved SFI but that a significant improvement of ROM was only found in rats with LLLT at 8 J/cm². Furthermore, the myelin sheath thickness and GAP43 expression levels were significantly enhanced in sciatic nerve-crushed rats receiving 808-nm LLLT at 3 and 8 J/cm². Taken together, these results suggest that 808-nm LLLT at a low energy density (3 J/cm² and 8 J/cm²) is capable of enhancing sciatic nerve regeneration following a crush injury.     

Increased cAMP as a positive inotropic factor for mammalian skeletal muscle in vitro

To test the hypothesis that an increased cAMP concentration improves skeletal muscle force development, we stimulated mouse soleus and extensor digitorum longus (EDL) in the presence of isoproterenol (1 x 10(-5) mol.L-1), a beta-adrenergic agonist, or N6,2'-O-dibutyryladenosine 3':5'-cyclic monophosphate (dcAMP) (1 x 10(-3) mol.L-1), a membrane-permeable cAMP analogue. Drugs used in the challenges were dissolved in Krebs-Henseleit bicarbonate buffer (Krebs) at 27 degrees C and gassed with 95% O2 - 5% CO2. Stimulation at 50 impulses.s-1 for 0.5 s produced an isometric tetanic contraction. Over 25 min of contractions at 0.6 contractions.min-1, developed force increased significantly with the addition of isoproterenol (soleus, 2.5% +/- 1.1%; EDL, 13.8% +/- 2.0%) or dcAMP (soleus, 2.3% +/- 0.5%; EDL, 10.9% +/- 1.9%) as compared with vehicle controls (cont) with Krebs added (soleus, 0.0% +/- 0.2%; EDL, -2.5% +/- 0.7%). To investigate the role of Ca2+ availability, we amplified or attenuated sarcolemmal L-type Ca2+ channels with Bay K 8644 (Bay K) (5.6 x 10(-6) mol.L-1) or diltiazem hydrochloride (dilt) (10(-4) mol.L-1), respectively. Ca2+ release from the sarcoplasmic reticulum was increased with caffeine (2 x 10(-3) mol.L-1) or decreased with dantrolene sodium (dant) (4.2 x 10(-7) mol.L-1). With Ca2+availability modified, dcAMP addition in soleus significantly increased force development above control (cont, 2.3% +/- 0.4%; Bay K, 4.0% +/- 1.0%; dilt, 52.3% +/- 3.6%; caffeine, 2.3% +/- 0.7%; dant, 6.0% +/- 2.0%; dilt + dant, 55.0% +/- 23.0%). In EDL, the addition of dcAMP also increased force development above control (cont, 13.7% +/- 1.9%; Bay K, 17.0% +/- 4.0%; dilt, 170.0% +/- 40.0%; caffeine, 23.0% +/- 4.0%; dant, 72.0% +/- 10.0%; dilt + dant, 54.0% +/- 14.0%). Thus, a positive inotropic effect of cAMP existed in both fast- and slow-twitch mammalian skeletal muscle with both normal and altered Ca2+ flux into the sarcoplasm.     

Effect of low-level laser therapy on the expression of inflammatory mediators and on neutrophils and macrophages in acute joint inflammation

Introduction

Inflammation of the synovial membrane plays an important role in the pathophysiology of osteoarthritis (OA). The synovial tissue of patients with initial OA is characterized by infiltration of mononuclear cells and production of proinflammatory cytokines and other mediators of joint injury. The objective was to evaluate the effect of low-level laser therapy (LLLT) operating at 50 mW and 100 mW on joint inflammation in rats induced by papain, through histopathological analysis, differential counts of inflammatory cells (macrophages and neutrophils), as well as gene expression of interleukin 1-beta and 6 (IL-1β and IL-6), and protein expression of tumor necrosis factor alpha (TNFα).

Methods

Male Wistar rats (n = 60) were randomly divided into four groups of 15 animals, namely: a negative control group; an inflammation injury positive control group; a 50 mW LLLT group, subjected to injury and treated with 50 mW LLLT; and a 100 mW LLLT group, subjected to injury and treated with 100 mW LLLT. The animals were subject to joint inflammation (papain solution, 4%) and then treated with LLLT (808 nm, 4 J, 142.4 J/cm², spot size 0.028 for both groups). On the day of euthanasia, articular lavage was collected and immediately centrifuged; the supernatant was saved for analysis of expression of TNFα protein by enzyme-linked immunosorbent assay and expression of IL-1β and IL-6 mRNA by real-time polymerase chain reaction. A histologic examination of joint tissue was also performed. For the statistical analysis, analysis of variance with Tukey''s post-hoc test was used for comparisons between each group. All data are expressed as mean values and standard deviation, with P < 0.05.

Results

Laser treatment with 50 mW was more efficient than 100 mW in reducing cellular inflammation, and decreased the expression of IL-1β and IL-6. However, the 100 mW treatment led to a higher reduction of TNFα compared with the 50 mW treatment.

Conclusions

LLLT with 50 mW was more efficient in modulating inflammatory mediators (IL-1β, IL-6) and inflammatory cells (macrophages and neutrophils), which correlated with the histology that showed a reduction in the inflammatory process.