Pinocytose

Pinocytose, more commonly called pinocytosis, is a cellular process by which cells internalize extracellular fluid and dissolved solutes through small vesicles formed at the plasma membrane. It is a form of endocytosis often described as for “cell drinking” and is distinct from phagocytosis, which engulfs solid particles.

Most pinocytosis is constitutive and non-specific, supporting routine nutrient uptake and membrane turnover. A related pathway, receptor-mediated pinocytosis, involves receptors that bind specific ligands and are concentrated in clathrin-coated pits, enabling selective uptake of molecules such as transferrin-bound iron or low-density lipoprotein. Vesicle sizes in receptor-mediated pinocytosis are typically on the order of 50–200 nanometers, though larger vesicles can form in other variants of the process.

Macropinocytosis is a related form of bulk pinocytosis driven by actin remodeling that creates extensive membrane ruffles and large vesicles called macropinosomes. This pathway is prominent in dendritic cells and macrophages, where it contributes to immune surveillance and antigen sampling, and can be stimulated by growth factors or certain pathogens.

After internalization, vesicles traffic to early endosomes, where solutes may be released into the cytosol, sorted, or directed to lysosomes for degradation. Receptor–ligand complexes are often recycled back to the plasma membrane. Pinocytosis plays a key role in nutrient acquisition and receptor regulation, and it can be exploited by some pathogens to gain cellular entry.