- Paracellular transport in the stomach epithelium plays a crucial but highly regulated role in maintaining mucosal homeostasis and barrier function.
- The gastric epithelium is organized into a tight monolayer of epithelial cells joined by tight junctions, which restrict and control the movement of substances between the stomach lumen and the underlying tissue.
- While transcellular transport is the dominant route for selective secretion and absorption, the paracellular pathway contributes to passive ion and water movement under normal conditions.
- In the stomach, tight junctions are essential to prevent back-diffusion of hydrogen ions (H⁺) from the acidic gastric lumen into the mucosa. Proteins such as claudin-18, occludin, and ZO-1 form the tight junctional complex and are critical in sealing the paracellular space. Claudin-18, in particular, is highly expressed in the gastric epithelium and functions as a barrier-forming claudin that restricts proton permeability. Loss or dysfunction of these junctional proteins leads to increased paracellular permeability, which can contribute to mucosal damage, inflammation, and eventually gastric disease.
- Pathological conditions such as Helicobacter pylori infection can significantly impact paracellular transport in the stomach. H. pylori disrupts tight junction integrity through various mechanisms, including the delivery of the CagA effector protein into epithelial cells. CagA interacts with host signaling molecules and junctional proteins, causing mislocalization or degradation of tight junction components like ZO-1 and occludin. This results in a compromised barrier that allows the unregulated passage of ions, protons, and potentially harmful luminal contents, contributing to epithelial injury and inflammation.
- In summary, paracellular transport in the stomach is normally restricted by robust tight junctions to preserve the acid barrier and mucosal integrity. Disruption of this control—through infection, inflammation, or genetic defects—can enhance paracellular permeability and promote gastric pathology. Understanding how tight junctions regulate paracellular transport in the stomach is therefore critical for studying gastric diseases, including ulcers and H. pylori-associated carcinogenesis.
