Angelides K J, Elmer L W, Loftus D, Elson E
Department of Physiology and Molecular Biophysics, Baylor College of Medicine, Houston, Texas 77030.
J Cell Biol. 1988 Jun;106(6):1911-25. doi: 10.1083/jcb.106.6.1911.
Voltage-dependent sodium channels are distributed nonuniformly over the surface of nerve cells and are localized to morphologically distinct regions. Fluorescent neurotoxin probes specific for the voltage-dependent sodium channel stain the axon hillock 5-10 times more intensely than the cell body and show punctate fluorescence confined to the axon hillock which can be compared with the more diffuse and uniform labeling in the cell body. Using fluorescence photobleaching recovery (FPR) we measured the lateral mobility of voltage-dependent sodium channels over specific regions of the neuron. Nearly all sodium channels labeled with specific neurotoxins are free to diffuse within the cell body with lateral diffusion coefficients on the order of 10(-9) cm2/s. In contrast, lateral diffusion of sodium channels in the axon hillock is restricted, apparently in two different ways. Not only do sodium channels in these regions diffuse more slowly (10(-10)-10(-11) cm2/s), but also they are prevented from diffusing between axon hillock and cell body. No regionalization or differential mobilities were observed, however, for either tetramethylrhodamine-phosphatidylethanolamine, a probe of lipid diffusion, or FITC-succinyl concanavalin A, a probe for glycoproteins. During the maturation of the neuron, the plasma membrane differentiates and segregates voltage-dependent sodium channels into local compartments and maintains this localization perhaps either by direct cytoskeletal attachments or by a selective barrier to channel diffusion.
电压依赖性钠通道在神经细胞表面分布不均匀，定位于形态学上不同的区域。对电压依赖性钠通道具有特异性的荧光神经毒素探针，对轴突起始段的染色强度比对细胞体强5 - 10倍，并显示出局限于轴突起始段的点状荧光，这与细胞体中更弥散和均匀的标记形成对比。我们使用荧光光漂白恢复技术（FPR）测量了电压依赖性钠通道在神经元特定区域的侧向迁移率。几乎所有用特异性神经毒素标记的钠通道都能在细胞体内自由扩散，侧向扩散系数约为10^(-9) cm²/s。相比之下，轴突起始段钠通道的侧向扩散受到限制，显然有两种不同的方式。这些区域的钠通道不仅扩散得更慢（10^(-10) - 10^(-11) cm²/s），而且它们被阻止在轴突起始段和细胞体之间扩散。然而，对于脂质扩散探针四甲基罗丹明 - 磷脂酰乙醇胺或糖蛋白探针异硫氰酸荧光素 - 琥珀酰伴刀豆球蛋白A，未观察到区域化或差异迁移率。在神经元成熟过程中，质膜分化并将电压依赖性钠通道分隔到局部区域，并可能通过直接的细胞骨架附着或对通道扩散的选择性屏障来维持这种定位。
