Hargittai P T, Butt A M, Lieberman E M
Department of Physiology, School of Medicine, East Carolina University, Greenville, NC 27858.
Neuroscience. 1990;38(1):163-73. doi: 10.1016/0306-4522(90)90382-e.
Selective ion permeability, ion transport properties, and electrical resistance of the perineurial barrier, as they relate to interstitial ion regulation, where studied and characterized electrophysiologically in ion substitution experiments. In high external [K+] a transient spike-like voltage was generated across the perineurial barrier which fell over 1-2 min to a slowly decaying voltage. The glial perineurium had at least a 10 times greater permeability to K+ than Cl-, and was effectively impermeant to Na+. The potential, in high external [K+], was determined by the K+ and Cl- gradients and their relative permeabilities across the sheath. For other cations the selectivity sequence of the perineurial barrier, as determined from electrophysiological measurements, was K+ greater than or equal to Rb+ much greater than NH4+ greater than Cs+ greater than Li+ greater than Na+ corresponding most closely to the Eisenman sequence IV. The perineurium had a resistance of 260 +/- 23 omega cm2 in crayfish physiological solution. In high [K+]0 the resistance fell by over half during the transient spike potential and then recovered towards resting levels as the voltage decayed. In the intact nerve cord interstitial [K+] rose to only 10-20 mM during a 2-min exposure to 100 mM K0+. K influx and efflux were related to the change in barrier permeability and an increased selectivity to K+ which, in these studies, was determined primarily by its electrochemical gradient across the perineurial barrier. The results suggest that the crayfish perineurium is a leaky epithelium capable of a high degree of ion regulation. Trans-perineurial barrier potential and conductance in high external [K+] are primarily functions of passive processes of the perineurial glial cell membranes and of the paracellular conductance channels driven by the electrochemical gradient for the K+. Accordingly, the mass transport of [K+] showed the same quantitative relationship in both directions.
在离子替代实验中，研究并通过电生理学方法表征了神经束膜屏障的选择性离子通透性、离子转运特性和电阻，这些特性与间质离子调节相关。在高外部[K⁺]浓度下，神经束膜屏障上会产生一个短暂的尖峰状电压，该电压在1 - 2分钟内下降至缓慢衰减的电压。神经胶质束膜对K⁺的通透性至少比对Cl⁻大10倍，且对Na⁺基本不通透。在高外部[K⁺]浓度下，电位由K⁺和Cl⁻梯度及其跨鞘的相对通透性决定。对于其他阳离子，根据电生理学测量确定的神经束膜屏障的选择性顺序为：K⁺≥Rb⁺>>NH₄⁺>Cs⁺>Li⁺>Na⁺，与艾森曼序列IV最为接近。在小龙虾生理溶液中，束膜电阻为260±23Ω·cm²。在高[K⁺]₀浓度下，在短暂的尖峰电位期间电阻下降超过一半，然后随着电压衰减恢复到静息水平。在完整的神经索中，在暴露于100 mM K₀⁺ 2分钟期间，间质[K⁺]仅上升至10 - 20 mM。K⁺的流入和流出与屏障通透性的变化以及对K⁺选择性的增加有关，在这些研究中，这主要由其跨神经束膜屏障的电化学梯度决定。结果表明，小龙虾的神经束膜是一种能够进行高度离子调节的渗漏上皮。在高外部[K⁺]浓度下，跨神经束膜屏障电位和电导主要是神经束膜胶质细胞膜被动过程以及由K⁺电化学梯度驱动的细胞旁电导通道的功能。因此，[K⁺]的质量传输在两个方向上显示出相同的定量关系。
