Patching and Capping

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The aggregation of fluorescently tagged antibodies that are associated with proteins on membranes of living cells. The aggregation appears as a cap or a patch in the fluorescence microscope and is due to the bivalent nature of antibodies. Patching and capping were critical in demonstrating the fluid nature of plasma membranes.

When the ligand binds to its specific receptor, the ligand-receptor complex accumulates in the coated pits. In many cells, these pits and complexes begin to concentrate in one area of a cell. Cytochemically, this appears as patches of label on the cell surface (patching) Eventually, the patches coalesce to form a cap at one pole of the cell (capping). Not all cells form caps, but most do form patches. The pre-concentration process minimizes the amount of fluid that is taken up in the vesicle.