Müntener M, Käser L, Weber J, Berchtold M W
Institute of Anatomy, University of Zürich-Irchel, Switzerland.
Proc Natl Acad Sci U S A. 1995 Jul 3;92(14):6504-8. doi: 10.1073/pnas.92.14.6504.
Parvalbumin (PV) is a high affinity Ca(2+)-binding protein found at high concentration in fast-contracting/relaxing skeletal muscle fibers of vertebrates. It has been proposed that PV acts in the process of muscle relaxation by facilitating Ca2+ transport from the myofibrils to the sarcoplasmic reticulum. However, on the basis of metal-binding kinetics of PV in vitro, this hypothesis has been challenged. To investigate the function of PV in skeletal muscle fibers, direct gene transfer was applied in normal and regenerating rat soleus muscles which do not synthesize detectable amounts of PV. Two weeks after in vivo transfection with PV cDNA, considerable levels of PV mRNA and protein were detected in normal muscle, and even higher amounts were detected in regenerating muscle. Twitch half-relaxation time was significantly shortened in a dose-dependent way in transfected muscles, while contraction time remained unaltered. The observed shortening of half-relaxation time is due to PV and its ability to bind Ca2+, because a mutant protein lacking Ca(2+)-binding capacity did not promote any change in physiology. These results directly demonstrate the physiological function of PV as a relaxing factor in mammalian skeletal muscle.
小白蛋白（PV）是一种高亲和力的钙结合蛋白，在脊椎动物快速收缩/舒张的骨骼肌纤维中含量很高。有人提出，PV通过促进钙离子从肌原纤维向肌浆网的转运，在肌肉舒张过程中发挥作用。然而，基于PV在体外的金属结合动力学，这一假设受到了挑战。为了研究PV在骨骼肌纤维中的功能，将直接基因转移技术应用于正常和正在再生的大鼠比目鱼肌，这些肌肉不会合成可检测到的PV。用PV cDNA进行体内转染两周后，在正常肌肉中检测到相当水平的PV mRNA和蛋白质，在再生肌肉中检测到的量甚至更高。在转染的肌肉中，颤搐半舒张时间以剂量依赖的方式显著缩短，而收缩时间保持不变。观察到的半舒张时间缩短是由于PV及其结合钙离子的能力，因为缺乏钙结合能力的突变蛋白没有引起任何生理变化。这些结果直接证明了PV作为哺乳动物骨骼肌舒张因子的生理功能。
