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首页> 外文期刊>Journal of Molecular Biology >Physical structure of the excitable membrane of unmyelinated axons: X-ray scattering study and electrophysiological properties of pike olfactory nerve
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Physical structure of the excitable membrane of unmyelinated axons: X-ray scattering study and electrophysiological properties of pike olfactory nerve

机译：无髓轴突兴奋膜的物理结构：派克嗅神经的X射线散射研究和电生理特性

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The aim of this work was to elicit correlations between physical structure and physiological functions in excitable membranes. Freshly dissected pike olfactory nerves were studied by synchrotron radiation X-ray scattering experiments and their physiological properties were tested by electrophysiological techniques. The scattering spectra contained a sharply oriented equatorial component (i.e. normal to the nerve axis), and an isotropic background. After background subtraction, the equatorial component displayed a weak and fairly sharp spectrum of oriented microtubules, and a strong and diffuse band of almost the same shape and position as the band computed for an isolated myelin membrane. We ascribed this spectrum to the axonal membranes. Under the action of temperature and of two local anesthetics, the spectrum underwent a contraction (or expansion) in the s-direction, equivalent to the structure undergoing an expansion (or contraction) in the direction perpendicular to the plane of the membrane. The main observations were: (i) with increasing temperature, membrane thickness decreased with a thermal expansion coefficient equal to -0.97(+/-0.19) 10(-3) degreesC(-1). The polarity and amplitude of this coefficient are typical of lipid-containing systems with the hydrocarbon chains in a disordered conformation. The amplitude and propagation velocity of the compound action potentials were drastically and reversibly reduced by lowering the temperature from 20 degreesC to 5 degreesC. (ii) Exposing the nerve to two local anesthetics (tetracaine and dibucaine) had the effect of decreasing membrane thickness. Action potentials were fully inhibited by these anesthetics. (iii) Upon depolarization, induced by replacing NaCl with KCl in the outer medium, approximately 25% of the membranes were found to associate by apposing their outer faces. Electrophysiological activity was reversibly impaired by the KCl treatment. (iv) No detectable structural effect was observed upon exposing the nerves to tetrodotoxin or veratridine. Electrophysiological activity was fully impaired by tetrodotoxin and partially impaired by veratridine. The main conclusions of this work are that axonal membranes yield highly informative X-ray scattering spectra, and that these spectra are sensitive to the functional state of the nerve. These results pave the way to further studies of more direct physiological significance. (C) 2000 Academic Press. [References: 16]
机译：这项工作的目的是激发可激发膜中的物理结构和生理功能之间的相关性。通过同步辐射X射线散射实验研究了新鲜解剖的派克嗅觉神经，并通过电生理技术测试了它们的生理特性。散射光谱包含尖锐的赤道分量（即垂直于神经轴）和各向同性的背景。扣除背景后，赤道成分显示出微弱且相当尖锐的定向微管光谱，并且形成了与分离的髓磷脂膜所计算出的条带几乎相同的形状和位置的强条带和扩散条带。我们将此光谱归因于轴突膜。在温度和两种局部麻醉剂的作用下，光谱在s方向上发生收缩（或膨胀），等同于结构在垂直于膜平面的方向上发生膨胀（或收缩）。主要观察结果是：（i）随着温度的升高，膜厚度降低，热膨胀系数等于-0.97（+/- 0.19）10（-3）摄氏度（-1）。该系数的极性和幅度是烃链呈无序构型的含脂质系统的典型特征。通过将温度从20℃降低到5℃，可逆地大幅降低复合作用电位的幅度和传播速度。 （ii）将神经暴露于两种局部麻醉药（丁卡因和地布卡因）具有降低膜厚度的作用。这些麻醉剂完全抑制了动作电位。 （iii）在去极化时，通过在外部介质中用KCl替代NaCl而引起，发现约25％的膜通过并置其外表面而缔合。 KCl处理可逆地损害电生理活性。 （iv）将神经暴露于河豚毒素或维拉替丁后未观察到可检测的结构作用。河豚毒素会完全损害电生理活性，而维拉替丁会部分损害其电生理活性。这项工作的主要结论是，轴突膜会产生高信息量的X射线散射光谱，并且这些光谱对神经的功能状态敏感。这些结果为进一步研究更直接的生理意义铺平了道路。 （C）2000学术出版社。 [参考：16]

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