ION DIFFUSION MODIFIED BY TORTUOSITY AND VOLUME FRACTION IN THE EXTRACELLULAR MICRO-ENVIRONMENT OF THE RAT CEREBELLUM
ION DIFFUSION MODIFIED BY TORTUOSITY AND VOLUME FRACTION IN THE EXTRACELLULAR MICRO-ENVIRONMENT OF THE RAT CEREBELLUM
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DOI：
10.1113/jphysiol.1981.sp013981
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发表时间：
1981-01-01
影响因子：
5.5
通讯作者：
PHILLIPS, JM
中科院分区：
文献类型：
--
作者：
NICHOLSON, C;PHILLIPS, JM
使用离子选择性微量移液器和离子导入点源，在大鼠小脑细胞外空间的微环境中严格检查了离子扩散宏观定律的有效性。定义了体积平均、体积分数 (α) 和弯曲度 (λ) 的概念，并证明它们在理论上适合量化复杂介质（例如大脑）中的扩散。使用阳离子四甲基铵和四乙基铵以及阴离子α-萘磺酸盐和六氟砷酸盐进行扩散研究，所有这些在测量期间基本上保持在细胞外。扩散参数的测量时间为 50 秒，距离约为 0.1 毫米。琼脂凝胶中离子扩散系数的测量给出的值与文献中得出的值非常接近，从而证实了该方法的有效性。在测试的限度内，小脑的测量没有揭示离子电渗电流强度、电极分离、各向异性、不均匀性、电荷歧视或吸收的任何系统影响。所有离子测量的汇总数据给出了α。 = 0.21.+-。 0.02（平均值.+-平均值的标准误差）和.lambda。 = 1.55.+-。 0.05（平均值.+-平均值的标准误差）。细胞外空间占据大鼠小脑的约20%，并且小单价细胞外离子的扩散系数降低了2.4倍（即，λ2），而不考虑电荷符号。其总体效果是将小脑中任何离子源的表观强度增加λ2/α因子，在本例中大约为12倍，并且改变扩散的时间进程。如果明确考虑体积分数和弯曲度，则细胞外空间中的小离子在小脑中严格遵守宏观扩散定律。这些结论可能普遍适用于其他大脑区域和其他扩散物质。
The validity of the macroscopic laws of ion diffusion was critically examined within the microenvironment of the extracellular space in the rat cerebellum using ion-selective micropipettes and ionophoretic point sources. The concepts of volume averaging, volume fraction (.alpha.) and tortuosity (.lambda.) were defined and shown to be theoretically appropriate for quantifying diffusion in a complex medium such as the brain. Diffusion studies were made with the cations tetramethylammonium and tetraethylammonium and the anions .alpha.-naphthalene sulfonate and hexafluoroarsenate, all of which remained essentially extracellular during the measurements. Diffusion parameters were measured for a period of 50 s and over distances of the order of 0.1 mm. Measurements of the diffusion coefficients of the ions in agar gel gave values that were very close to those derivable from the literature, thus confirming the validity of the method. Measurements in the cerebellum did not reveal any systematic influences of ionophoretic current strength, electrode separation, anisotropy, inhomogeneity, charge discrimination or uptake, within the limits tested. The pooled data from measurements with all the ions gave .alpha. = 0.21 .+-. 0.02 (mean .+-. standard error of mean) and .lambda. = 1.55 .+-. 0.05 (mean .+-. standard error of mean). The extracellular space occupies about 20% of the rat cerebellum and that the diffusion coefficient for small monovalent extracellular ions is reduced by a factor of 2.4 (i.e., .lambda.2) without regard to charge sign. The over-all effect of this is to increase the apparent strength of any ionic source in the cerebellum by a factor of .lambda.2/.alpha., about 12-fold in the present case, and to modify the time course of diffusion. The laws of macroscopic diffusion are closely obeyed in the cerebellum for small ions in the extracellular space, provided that volume fraction and tortuosity are explicitly taken into account. These conclusions may be generally applicable to other brain regions and other diffusing substances.