Chair of Human Biology, Technical University of Munich, Freising, Germany.
Institute for Physiology and Cell Biology, University of Veterinary Medicine, Foundation, Hannover, Germany.
J Physiol. 2020 Dec;598(23):5317-5332. doi: 10.1113/JP280309. Epub 2020 Sep 16.
Neurons of the enteric submucous plexus are challenged by osmolar fluctuations during digestion and absorption of nutrients. Central neurons are very sensitive to changes in osmolality but knowledge on that issue related to enteric neurons is sparse. The present study focuses on investigation of osmosensitivity of submucosal neurons including potential molecular mediating mechanisms. Results show that submucosal neurons respond to hypoosmolar stimuli with increased activity which is partially mediated by the transient receptor potential vanilloid 4 channel. We provided important information on osmosensitive properties of enteric neurons. These data are fundamental to better explain the nerve-mediated control of the gastrointestinal functions during physiological and pathophysiological (diarrhoea) conditions.
Enteric neurons are located inside the gut wall, where they are confronted with changes in osmolality during (inter-) digestive periods. In particular, neurons of the submucous plexus (SMP), located between epithelial cells and blood vessels may sense and respond to osmotic shifts. The present study was conducted to investigate osmosensitivity of enteric submucosal neurons and the potential role of the transient receptor potential vanilloid 4 channel (TRPV4) as a mediator of enteric neuronal osmosensitivity. Therefore, freshly dissected submucosal preparations from guinea pig colon were investigated for osmosensitivity using voltage-sensitive dye and Ca imaging. Acute hypoosmolar stimuli (final osmolality reached at ganglia of 94, 144 and 194 mOsm kg ) were applied to single ganglia using a local perfusion system. Expression of TRPV4 in the SMP was quantified using qRT-PCR, and GSK1016790A and HC-067047 were used to activate or block the receptor, respectively, revealing its relevance in enteric osmosensitivity. On average, 11.0 [7.0/17.0] % of submucosal neurons per ganglion responded to the hypoosmolar stimulus. The Ca imaging experiments showed that glia responded to the hypoosmolar stimulus, but with a delay in comparison with neurons. mRNA expression of TRPV4 could be shown in the SMP and blockade of the receptor by HC-067047 significantly decreased the number of responding neurons (0.0 [0.0/6.3] %) while the TRPV4 agonist GSK1016790A caused action potential discharge in a subpopulation of osmosensitive enteric neurons. The results of the present study provide insight into the osmosensitivity of submucosal enteric neurons and strongly indicate the involvement of TRPV4 as an osmotransducer.
在营养物质的消化和吸收过程中，肠黏膜下丛神经元受到渗透压波动的挑战。中枢神经元对渗透压变化非常敏感，但有关肠神经元的相关知识却很少。本研究主要集中在研究黏膜下神经元的渗透压敏感性，包括潜在的分子介导机制。结果表明，黏膜下神经元对低渗刺激的反应是活性增加，部分是由瞬时受体电位香草酸 4 通道介导的。我们提供了有关肠神经元渗透压敏感性的重要信息。这些数据对于更好地解释生理和病理生理（腹泻）条件下胃肠功能的神经调节至关重要。
肠神经元位于肠壁内部，在（内）消化期间，它们会遇到渗透压的变化。特别是位于上皮细胞和血管之间的黏膜下神经丛（SMP）神经元可能会感知和响应渗透压的变化。本研究旨在研究肠黏膜下神经元的渗透压敏感性以及瞬时受体电位香草酸 4 通道（TRPV4）作为肠神经元渗透压敏感性的潜在介导物的作用。因此，使用电压敏感染料和 Ca 成像技术，对豚鼠结肠的黏膜下切片进行了渗透压敏感性研究。使用局部灌注系统，将急性低渗刺激（终末渗透压达到神经节 94、144 和 194 mOsm kg）应用于单个神经节。使用 qRT-PCR 定量 SMP 中的 TRPV4 表达，并用 GSK1016790A 和 HC-067047 分别激活或阻断该受体，揭示其在肠渗透压敏感性中的相关性。平均而言，每个神经节有 11.0[7.0/17.0]%的黏膜下神经元对低渗刺激有反应。Ca 成像实验表明，胶质细胞对低渗刺激有反应，但与神经元相比有延迟。SMP 中 TRPV4 的 mRNA 表达可以显示出来，而 HC-067047 阻断受体显著减少了有反应的神经元数量（0.0[0.0/6.3]%），而 TRPV4 激动剂 GSK1016790A 则导致一部分对渗透压敏感的肠神经元放电。本研究结果提供了对黏膜下肠神经元渗透压敏感性的深入了解，并强烈表明 TRPV4 作为渗透压传感器的参与。
