Biomedical Engineering Group, Division of Engineering, King's College London, Strand, London, WC2R 2LS, UK.
Analyst. 2010 Sep;135(9):2340-7. doi: 10.1039/c0an00260g. Epub 2010 Jul 2.
Serotonin (5-HT) is well known to be a key neurotransmitter within the gastrointestinal (GI) tract, where it is responsible for influencing motility. Obtaining dynamic information about the neurotransmission process (specifically the release and reuptake of 5-HT) requires the development of new approaches to measure the extracellular 5-HT concentration profile. In this work constant-potential amperometry has been utilised at +650 mV vs. Ag|AgCl to measure in vitro the overflow of 5-HT. Steady-state levels of 5-HT have been observed, due to continuous mechanical stimulation of the tissue from the experimental protocol. Measurements are conducted at varying tissue-electrode distances in the range of 5 to 1100 microm. The difference in the current from the bulk media and that from each tissue-electrode distance is obtained, and the natural log of this current is plotted versus the tissue-electrode distance. The linear fit to the log of the current is derived, and its intercept, I(0), with the vertical axis and its slope are calculated. The reciprocal of the slope, indicated as slope(-1), is used as a marker of reuptake. The ratio between intercept, I(0), and the reciprocal of the slope, I(0)/slope(-1), is a measure of the flux at the tissue surface and it can be used as a marker for the 5-HT release rate. Current measurements for ileum and colon tissue indicated a significantly higher reuptake rate in the colon, showed by a lower slope(-1). In addition, the ratio, I(0)/slope(-1), indicated that the colon has a higher 5-HT flux compared to the ileum. Following the application of the serotonin selective reuptake inhibitor (SSRI), fluoxetine, both tissues showed a higher value of slope(-1), as the reuptake process is blocked preventing clearance of 5-HT. No differences were observed in the ratio, I(0)/slope(-1), in the ileum, but a decrease was observed in the colon. These results indicate that ileum and colon are characterised by different reuptake and release processes. The new approach we propose provides pivotal information on the variations in the signalling mechanism, where steady state levels are observed and can be a vital tool to study differences between normal and diseased tissue and also the efficacy of pharmacological agents.
血清素（5-HT）是胃肠道（GI）中一种重要的神经递质，它负责影响运动。获得有关神经传递过程的动态信息（特别是 5-HT 的释放和再摄取）需要开发新的方法来测量细胞外 5-HT 浓度分布。在这项工作中，我们利用+650 mV 相对于 Ag|AgCl 的恒电位电流法测量了体外 5-HT 的溢出。由于实验方案中对组织的持续机械刺激，观察到 5-HT 的稳态水平。在 5 到 1100 微米的范围内，在不同的组织-电极距离下进行测量。从总体介质中获得电流与从每个组织-电极距离获得的电流之间的差值，并绘制该电流的自然对数与组织-电极距离的关系图。从该电流的对数得出线性拟合，计算其与垂直轴的截距 I(0)及其斜率。斜率的倒数，记为 slope(-1)，用作再摄取的标志物。截距 I(0)与斜率倒数 I(0)/slope(-1)的比值是组织表面通量的度量，可用作 5-HT 释放率的标志物。回肠和结肠组织的电流测量表明，在结肠中再摄取率显著较高，斜率(-1)较低。此外，I(0)/slope(-1)比值表明，与回肠相比，结肠具有更高的 5-HT 通量。在应用选择性 5-HT 再摄取抑制剂（SSRI）氟西汀后，两种组织的 slope(-1)值均升高，因为再摄取过程被阻断，阻止了 5-HT 的清除。在回肠中，I(0)/slope(-1)比值没有观察到差异，但在结肠中观察到下降。这些结果表明，回肠和结肠的再摄取和释放过程不同。我们提出的新方法提供了有关信号机制变化的关键信息，在该信号机制中观察到稳态水平，可以成为研究正常组织和患病组织之间差异以及药物疗效的重要工具。
