Intramembranous particle distribution at the node of Ranvier and adjacent axolemma in myelinated axons of the frog brain
Intramembranous particle distribution at the node of Ranvier and adjacent axolemma in myelinated axons of the frog brain
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蛙脑有髓轴突 Ranvier 结和邻近轴膜的膜内颗粒分布
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发表时间：
1976
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通讯作者：
J. Rosenbluth
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作者：
J. Rosenbluth
本文用冷冻断裂技术对蛙脑有髓轴突的质膜进行了研究。轴膜的细胞质小叶在结和结间区域含有许多随机分布的颗粒，但在结旁区域的轴舌交界部分含有相对较少的颗粒。轴膜外叶的颗粒分布甚至更不均匀，其中结节间区域的颗粒浓度较低，而朗维尔结处的颗粒浓度相对较高（约1200 μm−2）。结节状颗粒往往比大多数膜内颗粒大，直径接近200 μ m。小叶的结旁区几乎没有这样的颗粒，除了在狭窄的螺旋形“凹槽”中，其面对终止的神经胶质突起之间的细胞外裂隙。在某些地方，这条路径变宽，形成面积达10.3 μm2的“湖泊”，其中含有大量类似于节点处的大颗粒。在节点处的颗粒浓度与估计在该区域中的钠通道浓度在相同的范围内，并且根据它们的位置和浓度建议这些颗粒代表离子载体。颗粒在结旁区的分布表明，大的膜内颗粒不能自由进入膜的轴舌交界部分，因此这些颗粒沿着膜的结旁区的运动可能主要发生在螺旋穿过轴膜的该部分的“凹槽”的膜中。郎维叶结两侧的颗粒运动表面积的这种限制可能导致颗粒在结节处被捕获，从而有助于它们在结节轴膜中的浓度。
SummaryThe plasma membrane of myelinated axons in the frog brain has been examined by the freeze-fracture technique. The cytoplasmic leaflet of the axolemma contains numerous randomly distributed particles in nodal and internodal regions but relatively fewer particles in the axoglial junctional portion of the paranodal region. Particle distribution is even less uniform in the outer leaflet of the axolemma, which contains a low concentration of particles in the internodal region and a relatively high concentration at the node of Ranvier (∼1200 particles μm−2). The nodal particles tend to be larger than most intramembranous particles, approaching 200 Å diameter. The paranodal region of the leaflet is virtually devoid of such particles except in the narrow helical ‘groove’ which faces extracellular clefts between terminating glial processes. In places this pathway widens to form ‘lakes’ up to ∼0.3 μm2 area which contain large numbers of large particles resembling those at the node. The concentration of particles at the node is in the same range as the concentration of sodium channels estimated to be in this region and it is suggested on the basis of their location and concentration that these particles represent ionophores. The distribution of particles in the paranodal region suggests that the large intramembranous particles do not have free access to the axoglial junctional portion of the membrane and therefore the movement of such particles along the paranodal region of the membrane may occur primarily in the membrane of the ‘groove’ spiraling through this portion of the axolemma. Such a restriction in surface area for particle movements on either side of the node of Ranvier could result in trapping of particles at the node and thus contribute to their concentration in the nodal axolemma.