Benveniste H, Hansen A J, Ottosen N S
Institute of Neuropathology, Teilum Institute, Copenhagen, Denmark.
J Neurochem. 1989 Jun;52(6):1741-50. doi: 10.1111/j.1471-4159.1989.tb07252.x.
Microdialysis is an extensively used technique for the study of solutes in brain interstitial space. The method is based on collection of substances by diffusion across a dialysis membrane positioned in the brain. The outflow concentration reflects the interstitial concentration of the substance of interest, but the relationship between these two entities is at present unclear. So far, most evaluations have been based solely on calibrations in saline. This procedure is misleading, because the ease by which molecules in saline diffuse into the probe is different from that of tissue. We describe here a mathematical analysis of mass transport into the dialysis probe in tissue based on diffusion equations in complex media. The main finding is that diffusion characteristics of a given substance have to be included in the formula. These include the tortuosity factor (lambda) and the extracellular volume fraction (alpha). We have substantiated this by studies in a well-defined complex medium (red blood cell suspensions) as well as in brain. We conclude that the traditional calculation procedure results in interstitial concentrations that are too low by a factor of lambda 2/alpha for a given compound.
微透析是一种广泛应用于研究脑间质空间中溶质的技术。该方法基于通过位于脑内的透析膜扩散来收集物质。流出浓度反映了所关注物质的间质浓度，但目前这两个量之间的关系尚不清楚。到目前为止，大多数评估仅基于在盐溶液中的校准。这个过程具有误导性，因为盐溶液中的分子扩散到探针中的难易程度与组织中的不同。我们在此描述基于复杂介质中扩散方程的组织中透析探针质量传输的数学分析。主要发现是给定物质的扩散特性必须包含在公式中。这些特性包括曲折因子（λ）和细胞外体积分数（α）。我们通过在明确定义的复杂介质（红细胞悬液）以及脑中的研究证实了这一点。我们得出结论，对于给定化合物，传统的计算方法得出的间质浓度比实际值低λ²/α倍。
