Klug G A, Biedermann M, Houston M E, Stuart D, Mumby M, Stull J T
Department of Exercise and Movement Science, University of Oregon, Eugene 97403.
Can J Physiol Pharmacol. 1992 Jun;70(6):859-65. doi: 10.1139/y92-115.
The effect of 1-12 days of electrical stimulation (10 Hz) on the ability to phosphorylate the P-light chain of myosin was studied in rabbit tibialis anterior muscle. Myosin phosphorylation was induced by exposure of the stimulated muscle and that of the contralateral leg to a single conditioning stimulus train (5 Hz) for 25 s via the motor nerve. Isometric tension was measured as were the myosin light chain composition and the activities of the enzymes responsible for phosphorylation and dephosphorylation. A computer simulation of the potential effect of a stimulation-induced disruption of Ca2+ metabolism on phosphorylation was also performed. Chronic stimulation for as little as 1 day eliminated light chain phosphorylation and reduced the myosin light chain kinase activity by approximately 36%. Conversely, phosphatase activity and light chain composition were unaffected. The model demonstrated that a slight depression in the magnitude of the Ca2+ transient could potentially attenuate phosphorylation. The data suggest that phosphorylation of myosin is extremely sensitive to prolonged muscle activity. Furthermore, it appears more likely that this sensitivity is related to regulation of intracellular free Ca2+ than to the other elements of the calmodulin-dependent system for myosin phosphorylation examined.
在兔胫骨前肌中研究了1 - 12天的电刺激（10赫兹）对肌球蛋白P轻链磷酸化能力的影响。通过运动神经对受刺激肌肉和对侧腿给予单次条件刺激串（5赫兹）持续25秒，诱导肌球蛋白磷酸化。测量等长张力、肌球蛋白轻链组成以及负责磷酸化和去磷酸化的酶的活性。还进行了计算机模拟，以研究刺激诱导的Ca2+代谢紊乱对磷酸化的潜在影响。仅持续1天的慢性刺激就消除了轻链磷酸化，并使肌球蛋白轻链激酶活性降低了约36%。相反，磷酸酶活性和轻链组成未受影响。该模型表明，Ca2+瞬变幅度的轻微降低可能会减弱磷酸化。数据表明，肌球蛋白的磷酸化对长时间的肌肉活动极其敏感。此外，这种敏感性似乎更有可能与细胞内游离Ca2+的调节有关，而不是与所研究的肌球蛋白磷酸化的钙调蛋白依赖性系统的其他元素有关。
