SENSING PH AT THE GASTRIC SURFACE

胃必须在胃上皮分泌的盐酸中存活。经常存在的化合物（如非甾体抗炎药）或生物（幽门螺杆菌）会破坏胃屏障对酸的吸收，在屏障被破坏时导致溃疡，这加剧了这一挑战。碱性粘膜旁凝胶层是胃的第一道防线：保护胃上皮免受胃酸从腔内反扩散。我们开发了一种独特的方法来非侵入性地测量胃表面的pH值。使用共聚焦显微镜，我们对粘膜旁碱性层进行了成像，当腔内pH值改变为喂食胃中的值时，该碱性层转化为酸性层。我们的研究结果提出了一个胃表面pH调节的新模型，其中包括控制表面pH的转运蛋白的实质性变化。我们的目标是确定胃内调节腔内pH传感和表面pH调节的元件。主要使用大鼠或小鼠胃的体内共聚焦显微镜，我们的第一个目标是确定胃感知和响应腔内pH的基本要求。我们将a)确定从碱到酸分泌转化所需的腔内pH变化的时间和位置，b)测试腔内营养物质和缓冲液在表面pH调节中的作用。在第二个目标中，我们将质疑哪些分子是介导胃酸和碱分泌综合调节的腔内pH刺激的换能器。我们将关注生长抑素、PGE2和含有CGRP的辣椒素敏感传入神经的作用。我们将使用选择性生长抑素2型受体（SST2）的拮抗剂和激动剂来分析生长抑素的作用，并对SST2敲除小鼠进行平行研究。通过对COX-1和COX-2敲除小鼠的平行研究，将利用已知环氧化酶（COX）同种异构体的选择性抑制剂来探讨前列腺素合成的作用。辣椒素敏感传入事件将使用香草受体激动剂、CGRP受体激动剂和拮抗剂进行分析，同时对化学脱传入动物进行平行研究。第三个目标将探讨胃粘膜损伤如何破坏表面pH调节。我们将在双光子显微镜下产生胃上皮的显微病变。利用这种新的局灶性胃损伤模型，我们将实时跟踪表面pH调节和组织修复过程的中断。我们将询问阿司匹林是否通过破坏正常小鼠和cox敲除小鼠的腔内pH感应和表面pH调节来削弱胃屏障，阿司匹林是临床粘膜损伤的主要原因。我们将确定阿司匹林是否影响双光子显微镜造成的局灶性病变的修复。研究结果将整合对胃防御和酸碱分泌调节的理解。

The stomach must survive HCl secreted by the gastric epithelium. This challenge is heightened by the frequent presence of compounds (e.g. non-steroidal anti-inflammatory drugs) or organisms (Helicobacter pylori) which compromise the gastric barrier to acid, leading to ulcers when the barrier is breached. An alkaline juxtamucosal gel layer is the first line of gastric defense: acting to protect the gastric epithelium from back-diffusion of acid from the lumen. We have developed a unique approach to non-invasively measure pH at the gastric surface in vivo. Using confocal microscopy, we have imaged a juxtamucosal alkaline layer, which converts to an acid layer when luminal pH is changed to values found in the fed stomach. Our results suggest a new model of gastric surface pH regulation, which includes a substantial change in the transporters that control surface pH. Our objective is to define the elements regulating luminal pH sensing and surface pH regulation in the stomach. Using primarily in vivo confocal microscopy of rat or mouse stomach, our first aim will define fundamental requirements for the stomach to sense and respond to luminal pH. We will a) define the timing and location of luminal pH change required for conversion from alkali to acid secretion, and b) test the role of luminal nutrients and buffers in surface pH regulation. In the second aim, we will question which molecules are transducers of the luminal pH stimulus that mediate the integrated regulation of both gastric acid and alkali secretion. We will focus on the role of somatostatin, PGE2, and capsaicin-sensitive afferent nerves containing CGRP. The role of somatostatin will be analyzed using antagonists and agonists selective for the somatostatin type 2 receptor (SST2) with parallel studies of SST2-knockout mice. The role of prostaglandin synthesis will be approached using selective inhibitors of known cycloxygenase (COX) isoforms, with parallel studies of COX-1 and COX-2 knockout mice. Capsaicin-sensitive afferents will be analyzed using vanilloid receptor agonists, CGRP receptor agonists and antagonists, with parallel studies of chemically deafferented animals. The third aim will ask how gastric mucosal damage disrupts surface pH regulation. We will generate microscopic lesions in the gastric epithelium by two-photon microscopy. Using this new model of focal gastric damage, we will follow the disruptions in surface pH regulation and the tissue repair process in real time. We will ask if aspirin, a major cause of clinical mucosal damage, weakens the gastric barrier by disruption of luminal pH sensing and surface pH regulation in normal and COX-knockout mice. We will determine if aspirin affects the repair of focal lesions created by two-photon microscopy. Results will integrate understanding of gastric defense with regulation of acid and alkali secretion.