Kandarian S C, Peters D G, Favero T G, Ward C W, Williams J H
Department of Health Sciences, Boston University, Massachusetts 02215, USA.
Am J Physiol. 1996 Jun;270(6 Pt 1):C1588-94. doi: 10.1152/ajpcell.1996.270.6.C1588.
In the present study, we examined whether weight-bearing condition can regulate the sarcoplasmic reticulum (SR) Ca(2+)-release mechanism. Measurements of alpha 1-subunit dihydropyridine (alpha 1-DHP) and ryanodine receptor levels were made in hypertrophied fast-twitch plantaris muscles 5 wk after surgical removal of synergist muscles (increased weight bearing) and in atrophied slowtwitch soleus muscles (14 days of non-weight bearing) of the rat. Rates of AgNO3-induced SR Ca2+ release were measured with fura 2 as the Ca2+ indicator and pyrophosphate as the precipitating ion during vesicular Ca2+ loading. Ca(2+)-release rates were 38, 49, and 58% lower in vesicles from hypertrophied vs. control muscles at AgNO3 concentrations of 0.05, 0.5, and 5 microM, respectively (control = 18.2 +/- 1.4 microM.mg-1. min-1). Western blots showed no differences in the relative expression of alpha 1-DHP or ryanodine receptor when IIID5 (monoclonal) or GP3 (polyclonal) antibodies were used. There was also no difference in ryanodine (10 nM) binding in Ca(2+)-incubated SR vesicles from hypertrophied muscles, suggesting no difference in the number of channels. In contrast, expression of alpha 1-DHP and ryanodine receptors was increased by 144 and 157% in non-weight-bearing soleus muscles, respectively. Scatchard analysis of DHP binding showed a 40% increase in maximum binding capacity and no change in the dissociation constant with non-weight-bearing muscles. The direction of modification of the SR Ca(2+)-release mechanism is opposite with increased and decreased weight bearing, but the mechanism by which this is achieved appears to be different.
在本研究中，我们检测了负重状态是否能调节肌浆网（SR）的Ca(2+)释放机制。在大鼠手术切除协同肌（增加负重）5周后，对其肥大的快肌型比目鱼肌以及（非负重14天）萎缩的慢肌型比目鱼肌中的α1-亚基二氢吡啶（α1-DHP）和兰尼碱受体水平进行了测量。在囊泡Ca(2+)负载过程中，以fura 2作为Ca(2+)指示剂，焦磷酸作为沉淀离子，测量了AgNO3诱导的SR Ca2+释放速率。在AgNO3浓度分别为0.05、0.5和5 microM时，肥大肌肉囊泡中的Ca(2+)释放速率分别比对照肌肉低38%、49%和58%（对照 = 18.2 +/- 1.4 microM.mg-1.min-1）。当使用IIID5（单克隆）或GP3（多克隆）抗体时，蛋白质免疫印迹显示α1-DHP或兰尼碱受体的相对表达没有差异。在肥大肌肉的Ca(2+)孵育SR囊泡中，兰尼碱（10 nM）结合也没有差异，这表明通道数量没有差异。相比之下，非负重比目鱼肌中α1-DHP和兰尼碱受体的表达分别增加了144%和157%。对DHP结合的Scatchard分析显示，非负重肌肉的最大结合能力增加了40%，解离常数没有变化。SR Ca(2+)释放机制的改变方向在负重增加和减少时相反，但实现这一改变的机制似乎不同。
