Gerrits Karin, Pauw-Gommans Inge, van Engelen Baziel, de Haan Arnold
Institute for Fundamental and Clinical Human Movement Sciences, Research Institute MOVE, Faculty of Human Movement Sciences, VU University Amsterdam, The Netherlands.
Clin Physiol Funct Imaging. 2007 Jul;27(4):217-24. doi: 10.1111/j.1475-097X.2007.00740.x.
Patients with nemaline myopathy, a muscle disorder primarily affecting the thin filaments, suffer from weakness which is poorly understood. As disturbed excitation-contraction coupling has been suggested as a possible mechanism, the present study was designed to investigate whether the contractile properties of the knee-extensor muscles in patients from a single family with nemaline myopathy were different from able-bodied individuals. To assess central neural as well as more peripheral intrinsic aspects of muscle activation, isometric voluntary and electrically elicited quadriceps contractions were evoked at different knee angles. Interestingly, across the range of 30-70 degrees of knee flexion, the capacity to achieve maximal voluntary activation of the muscles, assessed by a super-imposed stimulation technique, was significantly higher in patients compared with controls. Furthermore, the torque-frequency relation differed between groups, with the muscles of patients producing higher torques at low (twitch and 10 Hz) stimulation frequencies relative to maximal (150 Hz) stimulation than controls at both 30 degrees and 60 degrees of knee flexion. These results suggest that no impairment was present at relatively low activation frequencies. It may, however, be indicative for a reduced cross-bridge attachment as part of the excitation-contraction coupling specifically at high activation frequencies. In conclusion, the quadriceps weakness observed in this specific patient group cannot be explained by an impaired capacity to maximally activate these muscles. However, the data of relatively high torques produced at submaximal activation frequencies are compatible with the hypothesis that patients with nemaline myopathy may have an impaired acto-myosin interaction specifically at high levels of activation.
杆状体肌病是一种主要影响细肌丝的肌肉疾病，患有该病的患者会出现肌无力症状，但其病因尚不清楚。由于兴奋 - 收缩偶联紊乱被认为是一种可能的机制，本研究旨在调查来自一个患有杆状体肌病的家族的患者的膝伸肌收缩特性是否与健康个体不同。为了评估肌肉激活的中枢神经以及更外周的内在方面，在不同的膝关节角度诱发了等长自愿和电刺激股四头肌收缩。有趣的是，在膝关节屈曲30 - 70度的范围内，通过叠加刺激技术评估，患者实现肌肉最大自愿激活的能力显著高于对照组。此外，两组之间的扭矩 - 频率关系不同，在膝关节屈曲30度和60度时，患者的肌肉在低（单收缩和10赫兹）刺激频率下相对于最大（150赫兹）刺激产生的扭矩高于对照组。这些结果表明在相对较低的激活频率下不存在损伤。然而，这可能表明作为兴奋 - 收缩偶联的一部分，尤其是在高激活频率下，横桥附着减少。总之，在这个特定患者群体中观察到的股四头肌无力不能用最大程度激活这些肌肉的能力受损来解释。然而，在次最大激活频率下产生相对高扭矩的数据与杆状体肌病患者可能在高水平激活时肌动蛋白 - 肌球蛋白相互作用受损的假设相符。
