Non-specific, adsorptive pinocytosis is a form of endocytosis, a process in which small particles are taken in by a cell by splitting off small vesicles from the cell surface. 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. The clathrin-coated pits occupy about 2% of the surface area of the cell and only last about a minute, with an estimated 2500 leaving the average cell surface each minute. The clathrin coats are lost almost immediately, and the membrane is subsequently recycled to the cell surface.
Alberts, Johnson, Lewis, Raff, Roberts, Walter: "Molecular Biology of the Cell", Fourth Edition, Copyright 2002 P.748