pinocytotic

Pinocytosis is a cellular process in which the plasma membrane invaginates to form small vesicles that internalize extracellular fluid and dissolved solutes. The adjective pinocytotic describes cells, vesicles, or processes that perform pinocytosis. This form of endocytosis is distinct from phagocytosis, which engulfs larger particles, and from receptor-mediated endocytosis, which is highly specific for particular ligands.

Pinocytosis encompasses several related pathways. Micropinocytosis involves the formation of small vesicles through modest membrane invagination and is typically constitutive and non-specific. Macropinocytosis produces larger vesicles via substantial membrane ruffling and actin remodeling; it can be stimulated by growth factors and is especially prominent in macrophages and dendritic cells. Both pathways require energy and cytoskeletal dynamics, with actin remodeling playing a key role in vesicle scission from the plasma membrane.

Regulation of pinocytosis involves signaling networks that coordinate membrane trafficking and vesicle formation. Small GTPases and phosphoinositides help control membrane remodeling, vesicle budding, and uptake rate. While pinocytosis is generally non-specific, the efficiency and rate of uptake can vary by cell type and physiological state.

Physiological roles of pinocytotic activity include maintenance of membrane surface area, sampling of extracellular fluid for nutrients and signaling molecules, and antigen surveillance in immune cells. Pinocytosis also contributes to receptor turnover at the cell surface and can be exploited by certain pathogens to gain entry into cells.