ParazellulärflussAssays

ParazellulärflussAssays are in vitro methods used to quantify paracellular transport across epithelial or endothelial cell barriers. In these assays, cells are cultured on permeable supports (such as Transwell inserts) to form a polarized monolayer that separates an apical and a basolateral compartment. A hydrophilic tracer molecule is applied to the apical side, and its appearance on the basolateral side is quantified over time by fluorescence or radioactive measurement. The apparent permeability coefficient (Papp) is calculated from the rate of appearance, the surface area of the membrane, and the initial tracer concentration. TEER readings are often collected in parallel to monitor tight junction integrity.

Common tracers include mannitol, inulin, lucifer Yellow, sodium fluorescein, and FITC-dextrans, chosen for limited transcellular transport. The choice of tracer and cell model influences sensitivity to paracellular routes and size-selectivity.

ParazellulärflussAssays are used to assess barrier integrity, evaluate drug absorption potential, and screen effects of compounds on tight junctions, such as cytokines or inflammatory mediators. They are also employed in disease-model studies of the intestinal epithelium, blood-brain barrier, and renal tubule epithelia.

Considerations include ensuring a confluent monolayer, avoiding adsorption to plastics, controlling temperature and pH, and interpreting results alongside TEER or other barrier readouts. Limitations include differences between in vitro models and in vivo barriers and potential contributions from non-paracellular routes.