骨骼肌介电行为的理论模型仿真

在 10 0 Hz～ 10 0 MHz范围内 ,应用椭圆壳介电理论模型 ,经过模拟仿真蛙骨骼肌细胞的介电行为 ,确定了蛙骨骼肌细胞的椭圆壳模型各相参数。为将来对骨骼肌疲劳、肌营养不良和肌肉萎缩等病症的模型分析奠定理论基础。     

Force deficits after stretches of activated rat muscle-tendon complex with reduced collagen cross-linking

The forces produced during stretches of passive and activated muscles, and isometric force deficits after stretching of activated muscles were examined in rat plantor flexor muscle-tendon complexes with reduced collagen cross-links (pyridinoline). Female Sprague-Dawley rats (n=6, age 87 days) were injected twice daily for 43 days with β-aminopropionitrile (BAPN, 333 mg/kg/day i.p.), an inhibitor of lysyl oxidase, which is responsible for the production of collagen cross-links. The relative weights of the plantar flexor muscles were similar for BAPN and saline-injected (control, C) rats (n=6). Pyridinoline was lower in the tendon (22.9%), and in the plantaris (17.1%), and soleus (7.4%) muscles (P<0.05), with no changes observed in collagen content (hydroxyproline), as determined by high-pressure liquid chromatography. At an ankle position of 90°, groups had similar forces at 5, 10, 20, 40, 60 and 80 Hz before stretching. Forces at 40° with stretches of the passive muscles (five times from 90° to 40°) were lower for all stretches in BAPN-injected rats (P<0.05). Isometric force deficits resulting from stretches of activated muscles (80 Hz, 20 times from 90° to 40°, rest intervals 3 min) followed similar courses for BAPN-injected and C rats, and were 51.1 (2.4)% (C) and 54.7 (4.6)% (BAPN) before the last stretch. After 1 h of rest, isometric force deficits were 26% and 29% larger at 10 Hz and 5 Hz, respectively, in BAPN-treated rats (P<0.05). The reduction in BAPN-injected collagen cross-linking of the skeletal muscle-tendon complex reduced the forces produced during stretches without muscle stimulation (i.e. passive stretch), and stretching of activated muscles produced larger isometric force deficits only at low stimulation frequencies. Electronic Publication     

Conditioning of heteronymous H reflex in human temporalis muscle by stimulation of perioral afferents

A heteronymous H reflex in the temporalis muscle can be elicited by selective stimulation of the masseteric nerve. The present study aimed at defining the optimal amplitude of the H reflex to detect inhibitory changes induced by stimulation of the perioral afferents and at providing new information on the control of masticatory muscles. Sixteen healthy volunteers participated in the experiment. A conditioning stimulus (CS) to the perioral skin was applied at various delays before an ipsilateral selective masseteric nerve stimulation (test stimulus: TS) while the subject was clenching the teeth at 25% of the maximal voluntary contraction. Two intensities of CS and TS were employed, high and low. The peak-to-peak amplitude of the H reflex (TS) and the root-mean-square value of the preceding electromyography were measured and the data analyzed by three-way analysis of variance and Tukey's posthoc tests. For both intensities used the heteronymous H reflex in the temporalis muscle was significantly decreased by prior activation of perioral afferents for delays from 5 to 60 ms. With a delay of 5 and 35 ms the preceding EMG level was not changed, while it was reduced at 20 and 60 ms delay. The intensities used to elicit the heteronymous H reflex of the temporalis muscle were appropriate to detect a reduction in motoneuron excitability. The reduction in the H reflex without a change in the preceding EMG at 5 and 35 ms delays could be due to presynaptic inhibition of the masseteric afferents exerted by the ipsilateral perioral afferents.     

Effect of gaze direction on neck muscle activity during cervical rotation

Control of the neck muscles is coordinated with the sensory organs of vision, hearing and balance. For instance, activity of splenius capitis (SC) is modified with gaze shift. This interaction between eye movement and neck muscle activity is likely to influence the control of neck movement. The aim of this study was to investigate the effect of eye position on neck muscle activity during cervical rotation. In eleven subjects we recorded electromyographic activity (EMG) of muscles that rotate the neck to the right [right obliquus capitis inferior (OI), multifides (MF), and SC, and left sternocleidomastoid (SCM)] with intramuscular or surface electrodes. In sitting, subjects rotated the neck in each direction to specific points in range that were held statically with gaze either fixed to a guide (at three different positions) that moved with the head to maintain a constant intra-orbit eye position or to a panel in front of the subject. Although right SC and left SCM EMG increased with rotation to the right, contrary to anatomical texts, OI EMG increased with both directions and MF EMG did not change from the activity recorded at rest. During neck rotation SCM and MF EMG was less when the eyes were maintained with a constant intra-orbit position that was opposite to the direction of rotation compared to trials in which the eyes were maintained in the same direction as the head movement. The inter-relationship between eye position and neck muscle activity may affect the control of neck posture and movement.     

Fast- and slow-twitch isoforms (SERCA1 and SERCA2a) of sarcoplasmic reticulum Ca-ATPase are expressed simultaneously in chronically stimulated muscle fibers

 Using an immunohistochemical double-labeling technique, we observed that different isoforms of sarcoplasmic reticulum Ca-ATPase are co-expressed in single fibers of canine fast-twitch skeletal muscles stimulated chronically at low frequency. By 7 days of neuromuscular stimulation, the population of hybrid fibers expressing both SERCA1 and SERCA2a [fast- and slow-twitch isoforms of sarco(endo)plasmic reticulum Ca²⁺-ATPase] had increased from 1.5% to 9.2% of fibers. By 14 days of stimulation 90% of the pure fast-twitch fibers (expressing only SERCA1) were replaced by hybrid fibers. An additional 28 days of stimulation caused all fast-twitch fibers to express SERCA2a at the same level as found in nonstimulated slow-twitch fibers (expressing only SERCA2a). At this time, one-half of the previously hybrid fibers had become pure slow-twitch fibers. The remaining one-half of the hybrid fibers expressed SERCA1 at a very low level. Extending stimulation to 70 days did not further change the percentage of fibers that were slow-twitch or hybrid. Immunoblot studies at the whole-muscle level confirmed that changes in SERCA expression at 42 days of neuromuscular stimulation were complete. Immunohistochemical analysis of longitudinal sections of muscle showed that the changes in SERCA protein were uniform along the length of the muscle fiber, indicating that nuclei along its length responded equally to chronic stimulation. Received: 12 November 1996 / Received after revision and accepted: 16 December 1996     

Mechanical and energy characteristics during shortening in isolated type-1 muscle fibres from Xenopus laevis studied at maximal and submaximal activation

 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     

Maximal dynamic expiratory pressures with fast and slow inspirations

Maximal dynamic expiratory pressures are higher when forced expiration is preceded by a fast inspiration to total lung capacity (TLC) than when preceded by a slow inspiration and a few seconds pause at TLC. We hypothesized that these pressure differences are due to the stretch-shorten cycle (SSC), which refers to enhancement of muscle force when a concentric muscle contraction is immediately preceded by an eccentric contraction. Seven volunteers [36 (2) years; mean (SEM)] performed maximal forced expirations against minimal resistance with fast (F) or slow (S) maneuvers. F maneuvers consisted of a fast inspiration to TLC followed immediately by a fast expiration, whereas S consisted of a slow inspiration to TLC and a 4- to 5-s pause at TLC prior to forced expiration. We measured esophageal pressure (P _es), peak expiratory flow rate (PEFR), and the EMG activity of the transversus abdominis (Tr) by means of intramuscular fine-wire electrodes. The subjects performed several runs of each maneuver in a random order, and runs with the greatest expiratory P _es were analyzed. In comparison with S, F yielded greater P _es [182 (15) versus 167 (15) cmH₂O; P=0.003)] but similar PEFR [9.8 (0.7) versus 9.6 (0.7) l/s, P>0.05] and EMG activity of the Tr during forced expiration [221 (31) versus 208 (34) a.u., P>0.05]. Further analysis revealed significant EMG activity of Tr during end-inspiration (eccentric contraction) with F maneuvers only [73 (22) versus 32 (17) a.u., P<0.05]. We conclude that the ability of expiratory muscles to generate greater P _es with F maneuvers is related to the sequence of an eccentric contraction, which is followed immediately by concentric contraction in a manner analogous to SSC described in skeletal muscles. Electronic Publication     

Effects of β-escin and saponin on the transverse-tubular system and sarcoplasmic reticulum membranes of rat and toad skeletal muscle

 Mechanically skinned skeletal muscle fibres from rat and toad were exposed to the permeabilizing agents β-escin and saponin. The effects of these agents on the sealed transverse tubular system (t-system) and sarcoplasmic reticulum (SR) were examined by looking at changes in the magnitude of the force responses to t-system depolarization, the time course of the fluorescence of fura-2 trapped in the sealed t-system, and changes in the magnitude of caffeine-induced contractures following SR loading with Ca²⁺ under defined conditions. In the presence of 2 μg ml^–1β-escin and saponin, the response to t-system depolarization was not completely abolished, decreasing to a plateau, and a large proportion of fura-2 remained in the sealed t-system. At 10 μg ml^–1, both agents abolished the ability of both rat and toad preparations to respond to t-system depolarization after 3 min of exposure, but a significant amount of fura-2 remained in sealed t-tubules even after exposure to 100 μg ml^–1β-escin and saponin for 10 min. β-Escin took longer than saponin to reduce the t-system depolarizations and fura-2 content of the sealed t-system to a similar level. The ability of the SR to load Ca²⁺ was reduced to a lower level after treatment with β-escin than saponin. This direct effect on the SR occurred at much lower concentrations for rat (2 μg ml^–1β-escin and 10 μg ml^–1 saponin) than toad (10 μg ml^–1β-escin and 150 μg ml^–1 saponin). The reverse order in sensitivities to β-escin and saponin of t-system and SR membranes indicates that the mechanisms of action of β-escin and saponin are different in the two types of membrane. In conclusion, this study shows that: (1) β-escin has a milder action on the surface membrane than saponin; (2) β-escin is a more potent modifier of SR function; (3) simple permeabilization of membranes is not sufficient to explain the effects of β-escin and saponin on muscle membranes; and (4) the t-system network within muscle fibres is not a homogeneous compartment. Received: 18 November 1998 / Received after revision: 6 January 1999 / Accepted: 7 January 1999     

郃郎喘必消冲剂的药理研究

本文通过对小鼠急性毒性实验,抗炎实验,对胸腺脾脏的影响及对豚鼠在体、离体气管平滑肌作用实验,观察了郃郎喘必消冲剂的药理学效应。结果表明,该制剂无明显毒性,最大耐受量为1000g/kg/d。它有明显的对抗二甲苯致小鼠耳炎及延长组胺诱发哮喘发作潜伏期的作用,对豚鼠离体气管平滑肌无松驰作用,对小鼠胸腺和脾脏有使其重量减小的趋势,但与对照组比较无显著性差异。