Piinoktoosi

Piinoktoosi, the Finnish term for pinocytosis, is a form of endocytosis in which a cell takes up extracellular fluid and dissolved solutes through small vesicles formed by inward folding of the plasma membrane. It is generally non-specific in the solutes it internalizes and is distinct from phagocytosis, which engulfs large particles.

Pinocytosis occurs via several routes. Macropinocytosis produces relatively large vesicles called macropinosomes and is driven by actin-driven membrane ruffling and signaling pathways such as PI3K and Rac1. Other routes involve clathrin- or caveolin-mediated endocytosis, which can contribute to fluid uptake and uptake of specific receptors, but are more selective than classical pinocytosis.

Physiological roles include sampling of extracellular fluid and nutrients across many cell types. In the intestinal epithelium and kidney tubules, pinocytosis helps reclaim proteins and solutes from the lumen. In the immune system, macrophages and dendritic cells use macropinocytosis to survey their environment and sample antigens for presentation.

Regulation and trafficking are energy-dependent and rely on the cytoskeleton. Vesicle formation and scission involve a set of proteins, including dynamin in several endocytic routes, as well as Rab GTPases and SNAREs that coordinate vesicle trafficking and fusion with endosomes.

Clinical and research relevance includes the fact that some pathogens exploit pinocytic pathways to enter host cells. Understanding pinocytosis informs drug delivery and nanomedicine strategies designed to enhance cellular uptake of therapeutics.

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