Stollberg J, Fraser S E
Department of Physiology and Biophysics, College of Medicine, University of California, Irvine 92717.
J Cell Biol. 1990 Nov;111(5 Pt 1):2029-39. doi: 10.1083/jcb.111.5.2029.
Acetylcholine receptors become clustered at the neuromuscular junction during synaptogenesis, at least in part via lateral migration of diffusely expressed receptors. We have shown previously that electric fields initiate a specific receptor clustering event which is dependent on lateral migration in aneural muscle cell cultures (Stollberg, J., and S. E. Fraser. 1988. J. Cell Biol. 107:1397-1408). Subsequent work with this model system ruled out the possibility that the clustering event was triggered by increasing the receptor density beyond a critical threshold (Stollberg, J., and S. E. Fraser. 1990. J. Neurosci. 10:247-255). This leaves two possibilities: the clustering event could be triggered by the field-induced change in the density of some other molecule, or by a membrane voltage-sensitive mechanism (e.g., a voltage-gated calcium signal). Electromigration is a slow, linear process, while voltage-sensitive mechanisms respond in a rapid, nonlinear fashion. Because of this the two possibilities make different predictions about receptor clustering behavior in response to pulsed or alternating electric fields. In the present work we have studied subcellular calcium distributions, as well as receptor clustering, in response to such fields. Subcellular calcium distributions were quantified and found to be consistent with the predicted nonlinear response. Receptor clustering, however, behaves in accordance with the predictions of a linear response, consistent with the electromigration hypothesis. The experiments demonstrate that a local increase in calcium, or, more generally, a voltage-sensitive mechanism, is not sufficient and probably not necessary to trigger receptor clustering. Experiments with slowly alternating electric fields confirm the view that the clustering of acetylcholine receptors is initiated by a local change in the density of some non-receptor molecule.
在突触形成过程中，乙酰胆碱受体至少部分通过扩散表达的受体的横向迁移，聚集在神经肌肉接头处。我们之前已经表明，电场会引发特定的受体聚集事件，该事件依赖于无神经肌肉细胞培养物中的横向迁移（斯托尔伯格，J.，和 S. E. 弗雷泽。1988.《细胞生物学杂志》107:1397 - 1408）。随后对该模型系统的研究排除了聚集事件是由受体密度增加超过临界阈值触发的可能性（斯托尔伯格，J.，和 S. E. 弗雷泽。1990.《神经科学杂志》10:247 - 255）。这留下了两种可能性：聚集事件可能由电场诱导的其他某种分子密度变化触发，或者由膜电压敏感机制（例如电压门控钙信号）触发。电迁移是一个缓慢的线性过程，而电压敏感机制以快速的非线性方式做出反应。因此，这两种可能性对受体在脉冲或交变电场作用下的聚集行为做出了不同的预测。在本研究中，我们研究了亚细胞钙分布以及对这类电场的受体聚集情况。对亚细胞钙分布进行了量化，发现与预测的非线性反应一致。然而，受体聚集的行为符合线性反应的预测，这与电迁移假说一致。实验表明，局部钙增加，或者更一般地说，电压敏感机制，不足以且可能也没有必要触发受体聚集。用缓慢交变电场进行的实验证实了这样一种观点，即乙酰胆碱受体的聚集是由某种非受体分子密度的局部变化引发的。
