Tao L, Nicholson C
New York University Medical Center, Department of Physiology and Neuroscience, NY 10016, USA.
Neuroscience. 1996 Dec;75(3):839-47. doi: 10.1016/0306-4522(96)00303-x.
The apparent diffusion coefficient, D*, was measured in rat cortical slices and compared to the free diffusion coefficient, D, for three negatively charged proteins, lactalbumin (mol. wt = 14,500), ovalbumin (45,000) and bovine serum albumin (66,000). The temporal evolution of the spatial distribution of albumin molecules labeled with the Texas Red fluorophore was determined using integrative optical imaging at intervals after a brief pressure injection from a micropipette in slices of adult rat cerebral cortex and dilute agarose gel. Diffusion coefficients were obtained by fitting appropriate equations to the data. In slices at 34 degrees C, the values of D* (10(-7) cm2/s, mean +/- S.E.M.) for lactalbumin, ovalbumin and bovine serum albumin were 2.37 +/- 0.10, 1.60 +/- 0.08 and 1.63 +/- 0.07, respectively. In agarose gel, values of D (10(-7) cm2/s) were 11.87 +/- 0.20, 10.02 +/- 0.25 and 8.29 +/- 0.17, respectively. From these data the tortuosity factors, (D/D*)0.5, were calculated, with 2.24 obtained for lactalbumin, 2.50 for ovalbumin and 2.26 for bovine serum albumin. Previous optical measurements using dextrans with mol. wts of 40,000 and 70,000 gave tortuosities of 2.16 and 2.25, but in contrast previous determinations with ion-selective microelectrodes using the small cation tetramethylammonium (mol. wt = 74.1) give tortuosities of about 1.6. The results show that proteins as large as bovine serum albumin diffuse through brain extracellular space but are more hindered than smaller molecules. A simple model compared the differences in diffusion properties of bovine serum albumin, dopamine and nitric oxide in brain tissue and discussed the implications for volume transmission of chemical information between cells. The results are also relevant to the behavior of diffusible factors in brain development and the delivery of therapeutic agents.
在大鼠皮质切片中测量了表观扩散系数D*，并将其与三种带负电荷的蛋白质（乳白蛋白，分子量 = 14,500；卵白蛋白，45,000；牛血清白蛋白，66,000）的自由扩散系数D进行了比较。在从成年大鼠大脑皮质切片和稀琼脂糖凝胶中的微量移液器进行短暂压力注射后的不同时间间隔，使用积分光学成像确定了用德克萨斯红荧光团标记的白蛋白分子空间分布的时间演变。通过将适当的方程拟合到数据中来获得扩散系数。在34℃的切片中，乳白蛋白、卵白蛋白和牛血清白蛋白的D值（10⁻⁷cm²/s，平均值±标准误）分别为2.37±0.10、1.60±0.08和1.63±0.07。在琼脂糖凝胶中，D值（10⁻⁷cm²/s）分别为11.87±0.20、10.02±0.25和8.29±0.17。根据这些数据计算了曲折因子（D/D）⁰·⁵，乳白蛋白为2.24，卵白蛋白为2.50，牛血清白蛋白为2.26。先前使用分子量为40,000和70,000的葡聚糖进行的光学测量得到的曲折度为2.16和2.25，但相比之下，先前使用离子选择性微电极对小阳离子四甲基铵（分子量 = 74.1）的测定得到的曲折度约为1.6。结果表明，像牛血清白蛋白这么大的蛋白质可通过脑细胞外空间扩散，但比小分子受到的阻碍更大。一个简单的模型比较了牛血清白蛋白、多巴胺和一氧化氮在脑组织中扩散特性的差异，并讨论了其对细胞间化学信息体积传递的影响。这些结果也与脑发育中可扩散因子的行为以及治疗药物的递送有关。
