Sketelj J, Crne-Finderle N, Strukelj B, Trontelj J V, Pette D
Institute of Pathophysiology, School of Medicine, University of Ljubljana, 1000 Ljubljana, Slovenia.
J Neurosci. 1998 Mar 15;18(6):1944-52. doi: 10.1523/JNEUROSCI.18-06-01944.1998.
Acetylcholinesterase (AChE) mRNA levels are severalfold higher in fast rat muscles compared with slow. We hypothesized that AChE mRNA levels and AChE activity in the neuromuscular junction depend on a specific nerve-induced pattern of motor unit activation. Chronic low-frequency stimulation, mimicking the activation pattern in slow muscles, was applied to fast muscles in rats. Molecular forms of AChE were analyzed by velocity sedimentation, and AChE mRNA levels were analyzed by Northern blots. AChE mRNA levels in stimulated fast muscles dropped to 10-20% of control after 1 week and became comparable to those in slow soleus muscles. The activity of the junctional A12 AChE form in 35 d stimulated fast muscles decreased to 56% of control value, reaching that in the soleus muscle. Therefore, synaptic AChE itself depends on the muscle activation pattern. Complete inactivity after denervation also decreased the AChE mRNA level in fast muscles to <10% in 48 hr. In contrast, profuse fibrillations observed in noninnervated immature regenerating muscles maintain AChE mRNA levels at 80% of that in the innervated fast muscles. If protein synthesis was inhibited by cycloheximide, AChE mRNA levels in 3-d-old regenerating muscle, still containing myoblasts, increased approximately twofold. No significant increase after cycloheximide application was observed either in denervated mature fast muscles or in normal slow muscles. Low AChE mRNA levels observed in those muscles are probably not caused by decreased stability of AChE mRNA as demonstrated in myoblasts.
与慢肌相比，快肌中乙酰胆碱酯酶（AChE）的mRNA水平要高出数倍。我们推测，神经肌肉接头处的AChE mRNA水平和AChE活性取决于运动单位激活的特定神经诱导模式。对大鼠的快肌施加慢性低频刺激，模拟慢肌中的激活模式。通过速度沉降分析AChE的分子形式，通过Northern印迹分析AChE mRNA水平。刺激1周后，快肌中AChE mRNA水平降至对照的10% - 20%，与慢比目鱼肌中的水平相当。在刺激35天的快肌中，接头处A12 AChE形式的活性降至对照值的56%，达到比目鱼肌中的水平。因此，突触AChE本身取决于肌肉激活模式。去神经后完全失活也使快肌中的AChE mRNA水平在48小时内降至<10%。相反，在无神经支配的未成熟再生肌肉中观察到的大量肌纤维颤动使AChE mRNA水平维持在有神经支配的快肌的80%。如果用环己酰亚胺抑制蛋白质合成，3日龄仍含有成肌细胞的再生肌肉中的AChE mRNA水平会增加约两倍。在去神经支配的成熟快肌或正常慢肌中，应用环己酰亚胺后均未观察到显著增加。如在成肌细胞中所证明的，在这些肌肉中观察到的低AChE mRNA水平可能不是由AChE mRNA稳定性降低引起的。
