Miele M, Fillenz M
University Laboratory of Physiology, Oxford, UK.
J Neurosci Methods. 1996 Dec;70(1):15-9. doi: 10.1016/S0165-0270(96)00094-5.
A quantitative method consisting of the modification of the zero net flux technique was used to determine the extracellular concentration of ascorbate. A carbon paste electrode (CPE) held at constant potential was combined with a microdialysis probe through which various concentrations of ascorbate were locally infused. In experiments with bilateral CPEs, one of which was combined with a dialysis probe, no difference was observed in either basal or stimulated ascorbate currents. Addition of different concentrations of ascorbate to the perfusion fluid produced rapid changes in the voltammetric current due to ascorbate oxidation. Irrespective of the concentration of ascorbate infused, the current returned to basal level when the perfusion was stopped. The return was found to be more rapid after infusion of concentrations of ascorbate higher than the extracellular concentration than after perfusion with ascorbate-free solutions. This demonstrates that homeostasis of ascorbate occurs in vivo. The calculated point of zero net flux was 416 +/- 66 microM (n = 6). This represents the extracellular concentration of ascorbate.
采用一种对零净通量技术进行改良的定量方法来测定细胞外抗坏血酸盐的浓度。将保持在恒定电位的碳糊电极（CPE）与一个微透析探针相结合，通过该探针局部注入不同浓度的抗坏血酸盐。在双侧使用碳糊电极的实验中，其中一个与透析探针相结合，无论是基础状态还是刺激状态下的抗坏血酸盐电流均未观察到差异。向灌注液中添加不同浓度的抗坏血酸盐会因抗坏血酸盐氧化而使伏安电流迅速发生变化。无论注入的抗坏血酸盐浓度如何，当灌注停止时电流都会恢复到基础水平。结果发现，注入高于细胞外浓度的抗坏血酸盐后电流恢复得比用无抗坏血酸盐溶液灌注后更快。这表明抗坏血酸盐在体内存在稳态。计算得出的零净通量点为416±66微摩尔（n = 6）。这代表细胞外抗坏血酸盐的浓度。
