Chen K C, Nicholson C
Department of Physiology and Neuroscience, New York University Medical School, 550 First Avenue, New York, NY 10016, USA.
Proc Natl Acad Sci U S A. 2000 Jul 18;97(15):8306-11. doi: 10.1073/pnas.150338197.
Diffusion of molecules in brain extracellular space is constrained by two macroscopic parameters, tortuosity factor lambda and volume fraction alpha. Recent studies in brain slices show that when osmolarity is reduced, lambda increases while alpha decreases. In contrast, with increased osmolarity, alpha increases, but lambda attains a plateau. Using homogenization theory and a variety of lattice models, we found that the plateau behavior of lambda can be explained if the shape of brain cells changes nonuniformly during the shrinking or swelling induced by osmotic challenge. The nonuniform cellular shrinkage creates residual extracellular space that temporarily traps diffusing molecules, thus impeding the macroscopic diffusion. The paper also discusses the definition of tortuosity and its independence of the measurement frame of reference.
分子在脑细胞外间隙中的扩散受到两个宏观参数的限制，即曲折因子λ和体积分数α。最近对脑切片的研究表明，当渗透压降低时，λ增加而α减小。相反，随着渗透压升高，α增加，但λ达到一个平稳状态。通过使用均匀化理论和各种晶格模型，我们发现，如果在渗透压挑战引起的收缩或肿胀过程中脑细胞形状发生不均匀变化，那么λ的平稳行为就可以得到解释。细胞的不均匀收缩会产生残余的细胞外间隙，暂时困住扩散的分子，从而阻碍宏观扩散。本文还讨论了曲折度的定义及其与测量参考系的无关性。
