Johnson J D, Jiang Y, Rall J A
Department of Medical Biochemistry, The Ohio State University Medical Center, Columbus, Ohio 43210-1218 USA.
Biophys J. 1999 Mar;76(3):1514-22. doi: 10.1016/S0006-3495(99)77310-8.
Parvalbumin (PA) is an intracellular Ca2+-binding protein found in some muscle and nerves. Its ability to bind Ca2+ and facilitate skeletal muscle relaxation is limited by its Mg2+ off-rate. EDTA serves as an "artificial" PA in that it exhibited similar rate constants for Mg2+ (3 s-1) and Ca2+ (0.7 s-1) dissociation at 10 degrees C. When introduced into frog skeletal muscle, EDTA increased the relaxation rate by approximately 2.7-fold, and with increasing tetanus duration, EDTA lost its ability to contribute to relaxation (and Ca2+ sequestration) at its Mg2+ off-rate. Intracellular EDTA recovered its ability to contribute to muscle relaxation and Ca2+ sequestration at its Ca2+ off-rate. Like PA, EDTA's contribution to muscle relaxation and Ca2+ sequestration was more clearly observed when the SR Ca-ATPase was inhibited. Introduction of EDTA into rat soleus muscle, which has low [PA], increased the relaxation rate in a manner that was analogous to the way in which PA facilitates relaxation of frog skeletal muscle. Thus intracellular EDTA serves as an effective mimic of PA, and its use should aid in our understanding of PA's function in muscle and nerve.
小清蛋白（PA）是一种存在于某些肌肉和神经中的细胞内钙结合蛋白。其结合钙并促进骨骼肌松弛的能力受到其镁解离速率的限制。乙二胺四乙酸（EDTA）可作为一种“人工”小清蛋白，因为在10摄氏度时，它对镁（3 s⁻¹）和钙（0.7 s⁻¹）解离表现出相似的速率常数。当引入青蛙骨骼肌时，EDTA使松弛速率提高了约2.7倍，并且随着强直收缩持续时间的增加，EDTA以其镁解离速率失去了对松弛（和钙螯合）的作用能力。细胞内的EDTA以其钙解离速率恢复了对肌肉松弛和钙螯合的作用能力。与小清蛋白一样，当肌浆网钙ATP酶被抑制时，EDTA对肌肉松弛和钙螯合的作用更明显。将EDTA引入[小清蛋白]含量低的大鼠比目鱼肌中，其增加松弛速率的方式类似于小清蛋白促进青蛙骨骼肌松弛的方式。因此，细胞内的EDTA可有效模拟小清蛋白，其应用应有助于我们了解小清蛋白在肌肉和神经中的功能。
