Transcellular transport

For the complementary transport route, see Paracellular transport.

Transcellular transport involves the transportation of solutes by a cell through a cell. One classic example is the movement of glucose from the intestinal lumen to extracellular fluid by epithelial cells.

Epithelial cells use primary and secondary active transport, often in conjunction with passive diffusion through ion channels, to produce transcellular transport across epithelial tissues. This transport can either be absorption, transport from lumen (apical membrane surface) to blood, or secretion, transport from blood (basolateral membrane surface) to lumen.

The transcellular pathway of transport is important in the intestinal absorption of drug molecules, the other being the paracellular pathway. The transcellular pathway of transport include transcellular diffusion, active carrier mediated transportation, and transcytosis. The transcelluar diffusion simply involves the movement of solutes based on a diffusion gradient moving from an area of high concentration to an area of low concentration, however, the cell membrane is a hydrophobic environment and will not allow the passive diffusion of charged, hydrophilic, or zwitterion molecules. Active transport involves the use of energy to transport specific substrates across barriers, even against the concentration gradient. Macromolecules can sometimes be transported through transcytosis.

In contrast, paracellular transport is the transfer of substances across an epithelium by passing through an intercellular space between the cells.

• 1. It differs from transcellular transport, where the substances travel through the cell passing through both the apical membrane and basolateral membrane
• 2. Renal physiology. Transcellular transport is more likely to involve energy expenditure than paracellular transpoort.
• 3. Capillaries of the blood–brain barrier have only transcellular transport in contrast with normal capillaries which have both transcellular and paracellular transport.