UCL Queen Square Institute of Neurology, University College London, London, United Kingdom.
UCL Queen Square Institute of Neurology, University College London, London, United Kingdom.
Biophys J. 2021 Apr 20;120(8):1431-1442. doi: 10.1016/j.bpj.2021.02.012. Epub 2021 Feb 18.
In obstacle-filled media, such as extracellular or intracellular lumen of brain tissue, effective ion-diffusion permeability is a key determinant of electrogenic reactions. Although this diffusion permeability is thought to depend entirely on structural features of the medium, such as porosity and tortuosity, brain tissue shows prominent nonohmic properties, the origins of which remain poorly understood. Here, we explore Monte Carlo simulations of ion diffusion in a space filled with overlapping spheres to predict that diffusion permeability of such media decreases with stronger external electric fields. This dependence increases with lower medium porosity while decreasing with radial (two-dimensional or three-dimensional) compared with homogenous (one-dimensional) fields. We test our predictions empirically in an electrolyte chamber filled with microscopic glass spheres and find good correspondence with our predictions. A theoretical insight relates this phenomenon to a disproportionately increased dwell time of diffusing ions at potential barriers (or traps) representing geometric obstacles when the field strength increases. The dependence of medium ion-diffusion permeability on electric field could be important for understanding conductivity properties of porous materials, in particular for the accurate interpretation of electric activity recordings in brain tissue.
在充满障碍物的介质中，如脑组织的细胞外或细胞内腔，有效的离子扩散渗透性是电反应的关键决定因素。尽管这种扩散渗透性被认为完全取决于介质的结构特征，如孔隙率和曲折度，但脑组织表现出明显的非欧姆特性，其起源仍知之甚少。在这里，我们探索了在充满重叠球体的空间中离子扩散的蒙特卡罗模拟，以预测这种介质的扩散渗透性随外部电场的增强而降低。这种依赖性随着介质孔隙率的降低而增加，而随着与各向同性（一维）场相比的径向（二维或三维）场而降低。我们在充满微观玻璃球体的电解质室中对我们的预测进行了实证检验，并发现与我们的预测有很好的一致性。一种理论洞察力将这种现象与当场强增加时，扩散离子在代表几何障碍物的势垒（或陷阱）处的停留时间不成比例地增加联系起来。介质中离子扩散渗透性对电场的依赖性对于理解多孔材料的电导率特性可能很重要，特别是对于准确解释脑组织中的电活动记录。
