The highly motile human pathogen Helicobacter pylori lives deep in the gastric mucus layer. To identify which chemical gradient guides the bacteria within the mucus layer, combinations of luminal perfusion, dialysis, and ventilation were used to modify or invert transmucus gradients in anaesthetized Helicobacterinfected mice and Mongolian gerbils. Neither changes in lumen or arterial pH nor inversion of bicarbonate͞CO2 or urea͞ammonium gradients disturbed Helicobacter orientation. However, elimination of the mucus pH gradient by simultaneous reduction of arterial pH and bicarbonate concentration perturbed orientation, causing the bacteria to spread over the entire mucus layer. H. pylori thus uses the gastric mucus pH gradient for chemotactic orientation. Helicobacter pylori, a motile Gram-negative human pathogen that causes gastritis and duodenal and gastric ulcers and increases the risk of gastric cancer (1), lives within the gastric mucus layer. The majority of bacteria are located deep in the mucus, close to the surface of the epithelium. The mucus is continuously secreted in the glands and by surface epithelial cells and is degraded at the luminal surface (2). Because of this rapid mucus turnover, the bacteria need motility and spatial orientation to avoid being carried into the lumen, where the acidic pH inhibits growth and paralyzes motility (3, 4). Orientation therefore plays a central role in acute colonization and the chronic persistence of H. pylori.Motile bacteria sense chemical gradients by means of chemoreceptor proteins and relay the information to the flagellar motor (5). In the case of H. pylori, it must be a chemical gradient in the gastric mucus layer that guides the bacteria. Within the mucus layer, diffusion is effectively restricted, so that the concentration of most substances entering the mucus from the epithelial surface will remain constant through the entire width of the layer. Despite this, at least three chemical gradients are known to exist here: a proton (pH) gradient (2, 6), a bicarbonate͞CO 2 gradient (7,8), and, in the Helicobacter-infected mucosa, a urea͞ammonium gradient (9) created by bacterial urease. We hypothesized that H. pylori may use one or several of these transmucus gradients for orientation in vivo.We have previously developed a method to precisely determine the distribution and colonization density of Helicobacter felis in the gastric mucus of mice in vivo (3). This method uses a micromanipulator-controlled sampling device (10) to extract nanoliter samples from the mucus and mucosa of anesthetized animals. After immediate immobilization of the bacteria by cooling, the density and distribution of the bacteria can be studied by digital image processing.To identify gradients involved in the orientation of Helicobacter spp., we inverted or modified individual gradients in anesthetized H. pylori-infected Mongolian gerbils or H. felisinfected mice and studied the effect of these changes on the distribution of bacteria in the mucus layer. The data show that gastric Helicob...

The gastric H(+)/K(+)-ATPase is located within an infolding (secretory canaliculus) of the apical plasma membrane of gastric parietal cells. Our aim was to measure the pH values in the cytosol and canaliculus of the acid-secreting parietal cell and the adjacent gland lumen in situ. We used ultrafine double-barreled tip-sealed microelectrodes at high acceleration rates for intracellular and canalicular measurements. Immunohistochemical staining of the parietal cells was used to identify the track of the electrode and to estimate the position of the electrode tip at the time of the last intracellular measurement. En route to the deepest regions of the mucosa, where the average gland lumen pH was approximately 3, and on advancing in steps of 2 mum, the electrode entered the cytosol of the parietal cells, where the pH value was 7.4. Advancing the electrode further resulted, in several instances, in a sharp decrease in pH to an average value of 1.7 +/- 0.2, which we interpreted as the measurement within the canaliculus. When the electrode was advanced even further, the pH reading returned to the cytosolic value. From the difference in pH between the secreting canaliculus and the adjacent gland lumen, we concluded that the released acid was immediately buffered. Thus, the only cellular structure directly exposed to the highly acidic canalicular content is the apical membrane forming the canaliculus in the parietal cell.

Following mucus depletion, there is a decrease in surface cell pH(i) and crypt outlet pH values. The repair process is then characterized by extensive mucus secretion and local cessation of acid secretion.