During this assay, endothelial cells are placed on the upper layer of a cell permeable membrane and a solution containing the test agent is placed below the cell permeable membrane. Following an incubation period (3–18 hours), the cells that have migrated through the membrane are stained and counted. The membrane is usually coated with some extracellular matrix component (e.g. collagen) which facilitates both adherence and migration.¹
The main advantage of this assay is its detection sensitivity. Migration through the permeable filter can be caused by very low levels of angiogenic inducers. Prolonged studies are difficult, due to the fact that the test-agent concentration will quickly equalize between the compartment below the membrane and the compartment above the membrane. Another disadvantage is the relative difficulty in setting up the transwells. Commercially available transwells have alleviated this burden, but they are expensive.