Smith G W, Tasman-Jones C, Wiggins P M, Lee S P
Gastroenterology. 1985 Dec;89(6):1313-8. doi: 10.1016/0016-5085(85)90648-1.
Gastric mucus is thought to protect the underlying mucosal cells from mechanical hazards and back-diffusion of luminal H+. In health, a pH gradient exists across the mucus layer from the variable low pH of the lumen to a pH approaching neutrality at the epithelial cell surface. By current hypotheses this gradient is maintained by the combined effects of an unstirred layer, restricted or slowed diffusion of H+ in the mucus, and the epithelial cell secretion of bicarbonate, which is confined to the cell surface by the mucus layer. These mechanisms do not explain how H+ is secreted through mucus in the first place. Using a modified diffusion chamber we have shown that pig gastric mucus facilitates a low-efficiency Na+/H+ exchange--a property that helps to clarify some previously unexplained components of H+ secretion. When a solution containing Na+ was separated by a layer of fresh pig gastric mucus from a solution of similar pH containing a much lower concentration of sodium, the sodium-rich solution was electrically negative relative to the sodium-poor solution and its pH decreased significantly with time. A similar pH gradient developed when the barrier was a synthetic cation-exchange membrane, and one of opposite sign when it was an anion exchanger; no pH gradient developed across neutral barriers. It is suggested that similar electrical coupling of H+ diffusion to active Na+ transport might in vivo ensure that secreted H+ moves into the gastric lumen.
胃黏液被认为可保护其下方的黏膜细胞免受机械损伤以及管腔中氢离子的反向扩散影响。在健康状态下，黏液层存在一个pH梯度，从管腔中可变的低pH值到上皮细胞表面接近中性的pH值。根据目前的假说，这个梯度是由一个静止层、氢离子在黏液中扩散受限或减缓以及上皮细胞分泌碳酸氢盐（其被黏液层限制在细胞表面）的综合作用维持的。但这些机制并未解释氢离子最初是如何通过黏液分泌的。我们使用一个改良的扩散室表明，猪胃黏液促进了低效的钠/氢交换——这一特性有助于阐明一些之前无法解释的氢离子分泌成分。当含有钠离子的溶液通过一层新鲜猪胃黏液与pH相似但钠浓度低得多的溶液隔开时，富含钠的溶液相对于贫钠溶液呈电负性，且其pH随时间显著降低。当屏障是合成阳离子交换膜时也会形成类似的pH梯度，而当屏障是阴离子交换剂时则形成相反符号的梯度；中性屏障不会形成pH梯度。有人提出，在体内，氢离子扩散与主动钠转运之间类似的电偶联可能确保分泌的氢离子进入胃腔。
