- Transcellular transport refers to the movement of substances through epithelial or endothelial cells, as opposed to the paracellular route, which goes between cells. This process involves the sequential passage of molecules across both the apical (luminal) and basolateral (serosal) membranes of the cell, often requiring specialized transporters, channels, and endocytic mechanisms.
- In the stomach, transcellular transport is essential for the secretion of hydrochloric acid (HCl) and for maintaining mucosal balance. For example, parietal cells in the gastric epithelium transport hydrogen ions (H⁺) into the gastric lumen via the H⁺/K⁺-ATPase (proton pump) located on the apical membrane. This is coupled with chloride (Cl⁻) secretion, resulting in the formation of HCl, the main component of gastric acid. Water follows osmotically through aquaporins or other pathways, facilitating gastric juice formation.
- Transcellular absorption of ions like sodium (Na⁺) and potassium (K⁺) is also tightly regulated and involves ion channels and transporters on both sides of the cell. These transport processes are energy-dependent and often rely on electrochemical gradients maintained by the Na⁺/K⁺-ATPase on the basolateral membrane. In addition to ions, some nutrients and drugs can also be absorbed transcellularly, although this function is more prominent in the intestine than in the stomach.
- Unlike paracellular transport, which is typically passive and size-selective, transcellular transport can be highly selective, regulated, and directional. It allows cells to control what enters and exits the tissue and contributes to maintaining electrolyte balance, acid-base homeostasis, and defense against pathogens.
- In pathological conditions, such as H. pylori infection, transcellular transport mechanisms may be altered. For instance, the bacterium’s virulence factors can interfere with ion transporters or signaling pathways, affecting acid secretion and disrupting mucosal defenses.
