Department of Chemistry, Washington University, St. Louis, Missouri, USA.
Department of Radiology, University of Texas Southwestern Medical Center, Dallas, Texas, USA.
Magn Reson Med. 2018 Mar;79(3):1616-1627. doi: 10.1002/mrm.26781. Epub 2017 Jul 4.
To determine the intracellular water preexchange lifetime, τ , the "average residence time" of water, in the intracellular milieu of neurons and astrocytes. The preexchange lifetime is important for modeling a variety of MR data sets, including relaxation, diffusion-sensitive, and dynamic contrast-enhanced data sets.
Herein, τ in neurons and astrocytes is determined in a microbead-adherent, cultured cell system. In concert with thin-slice selection, rapid flow of extracellular media suppresses extracellular signal, allowing determination of the transcytolemmal-exchange-dominated, intracellular T . With this knowledge, and that of the intracellular T in the absence of exchange, τ can be derived.
Under normal culture conditions, τ for neurons is 0.75 ± 0.05 s versus 0.57 ± 0.03 s for astrocytes. Both neuronal and astrocytic τ s decrease within 30 min after the onset of oxygen-glucose deprivation, with the astrocytic τ showing a substantially greater decrease than the neuronal τ .
Given an approximate intra- to extracellular volume ratio of 4:1 in the brain, these data imply that, under normal physiological conditions, an MR experimental characteristic time of less than 0.012 s is required for a nonexchanging, two-compartment (intra- and extracellular) model to be valid for MR studies. This characteristic time shortens significantly (i.e., 0.004 s) under injury conditions. Magn Reson Med 79:1616-1627, 2018. © 2017 International Society for Magnetic Resonance in Medicine.
确定神经元和星形胶质细胞细胞内水的预交换寿命 τ，即水在细胞内环境中的“平均停留时间”。预交换寿命对于建模各种磁共振（MR）数据集（包括弛豫、扩散敏感和动态对比增强数据集）非常重要。
在此，通过微珠附着的培养细胞系统确定神经元和星形胶质细胞中的 τ。与薄片选择相结合，细胞外介质的快速流动抑制细胞外信号，允许确定跨细胞膜交换主导的细胞内 T。有了这些知识，以及在没有交换的情况下细胞内 T 的知识，可以推导出 τ。
在正常培养条件下，神经元的 τ 为 0.75±0.05 s，而星形胶质细胞的 τ 为 0.57±0.03 s。在缺氧葡萄糖剥夺开始后 30 分钟内，神经元和星形胶质细胞的 τ 均降低，星形胶质细胞的 τ 降低幅度明显大于神经元的 τ。
鉴于大脑中细胞内到细胞外的体积比约为 4:1，这些数据表明，在正常生理条件下，对于 MR 研究，一个无交换的两室（细胞内和细胞外）模型，其 MR 实验特征时间小于 0.012 s 才有效。在损伤条件下，这个特征时间会显著缩短（即 0.004 s）。磁共振医学 79：1616-1627，2018。©2017 国际磁共振学会。
