Stollberg J, Fraser S E
Department of Physiology and Biophysics, College of Medicine, University of California, Irvine 92717.
J Cell Biol. 1988 Oct;107(4):1397-408. doi: 10.1083/jcb.107.4.1397.
Using digitally analyzed fluorescence videomicroscopy, we have examined the behavior of acetylcholine receptors and concanavalin A binding sites in response to externally applied electric fields. The distributions of these molecules on cultured Xenopus myoballs were used to test a simple model which assumes that electrophoresis and diffusion are the only important processes involved. The model describes the distribution of concanavalin A sites quite well over a fourfold range of electric field strengths; the results suggest an average diffusion constant of approximately 2.3 X 10(-9) cm2/s. At higher electric field strengths, the asymmetry seen is substantially less than that predicted by the model. Acetylcholine receptors subjected to electric fields show distributions substantially different from those predicted on the basis of simple electrophoresis and diffusion, and evidence a marked tendency to aggregate. Our results suggest that this aggregation is due to lateral migration of surface acetylcholine receptors, and is dependent on surface interactions, rather than the rearrangement of microfilaments or microtubules. The data are consistent with a diffusion-trap mechanism of receptor aggregation, and suggest that the event triggering receptor localization is a local increase in the concentration of acetylcholine receptors, or the electrophoretic concentration of some other molecular species. These observations suggest that, whatever mechanism(s) trigger initial clustering events in vivo, the accumulation of acetylcholine receptors can be substantially enhanced by passive, diffusion-mediated aggregation.
我们使用数字分析荧光视频显微镜，研究了乙酰胆碱受体和伴刀豆球蛋白A结合位点在外部施加电场时的行为。这些分子在培养的非洲爪蟾肌球上的分布被用于测试一个简单模型，该模型假定电泳和扩散是唯一重要的相关过程。该模型在四倍电场强度范围内能很好地描述伴刀豆球蛋白A位点的分布；结果表明平均扩散常数约为2.3×10⁻⁹ cm²/s。在更高的电场强度下，观察到的不对称性明显小于模型预测值。受到电场作用的乙酰胆碱受体显示出与基于简单电泳和扩散预测的分布有很大不同，并且有明显的聚集倾向。我们的结果表明这种聚集是由于表面乙酰胆碱受体的横向迁移，并且依赖于表面相互作用，而不是微丝或微管的重排。这些数据与受体聚集的扩散陷阱机制一致，并且表明触发受体定位的事件是乙酰胆碱受体浓度的局部增加，或者是其他某种分子物种的电泳浓缩。这些观察结果表明，无论在体内触发初始聚集事件的机制是什么，乙酰胆碱受体的积累都可以通过被动的、扩散介导的聚集而显著增强。
