Pinocytosis

In endocytosis the cell plasma membrane extends and folds around desired extracellular material, forming a pouch that pinches off creating an internalized vesicle.

[7] Cationic proteins bind to the negative cell surface and are taken up via the clathrin-mediated system, thus the uptake is intermediate between receptor-mediated endocytosis and non-specific, non-adsorptive pinocytosis.

These ligands activate a complex signaling pathway, resulting in a change in actin dynamics and the formation of cell-surface protrusions of filopodia and lamellopodia, commonly called ruffles.

When ruffles collapse back onto the membrane, large fluid-filled endocytic vesicles form called macropinosomes, which can transiently increase the bulk fluid uptake of a cell by up to tenfold.

Macropinocytosis is a solely degradative pathway: macropinosomes acidify and then fuse with late endosomes or endolysosomes, without recycling their cargo back to the plasma membrane.