Pinocytosis adsorptive

Compared with phagocytosis, pinocytosis appears to be a universal phenomenon in all cells, including phagocytes. Unlike phagocytosis, which is mediated by the serum opsonin, pinocytosis does not require any external stimulus. Pinocytosis is divided into two types fluid-phase pinocytosis and adsorptive pinocytosis (see Fig. 3B). Fluid-phase pinocytosis is a nonspecific, continuous process, and it is believed to be useful as a general process for transporting macromolecular constructs through epithelia, some endothelia, and into various blood cells. Adsorptive pinocytosis, in... 

Fig. I. Endocytic pathways used by cells to internalize soluble macromolecules [25] fluid-phase pinocytosis (1), adsorptive pinocytosis (2), and receptor-mediated endocytosis (pinocytosis) (6). Each of these processes involves a formation of a sealed vesicle formed from the plasma membrane which encloses part of the extracellular medium. The internalization of a polymer-drug conjugate (P-D), and targeted polymer-drug conjugate ( => —P-D) is shown. Other abbreviations — = cell surface receptor/antigen 1 = clathrin molecule X = lysosomal enzyme. Fluid-phase pinocytosis (1) and adsorptive pinocytosis (2) are nonspecific processes which direct the macromolecule into the lysosomal compartment of the cell. Once P-D is internalized, whether by (1) or (2), the resulting endosome (3) is ultimately fused with a primary lysosome (4) forming a secondary lysosome (5). In the latter compartment P-D is in contact with several types of lysosomal enzymes. The membrane of (5) is impermeable to macromolecules. Consequently, the structure of P-D may be designed in such...

Compared with phagocytosis, fluid-phase pinocytic capture of molecules is relatively slower, being directly proportional to the concentration of macromolecules in the extracellular fluid. It is also dependent on the size of macromolecules in general, lower molar mass fractions are captured faster than the higher molar mass fractions. The magnitude of the rate of capture by adsorptive pinocytosis is higher than that by fluid-phase pinocytosis and relates to the nature of substrate-membrane interactions. 

With respect to the concentration factor, the molecules of the polymer can be found in the extracellular fluid either distributed randomly or forming some kind of concentration gradient with respect to the vicinity of the involved part of the cell surface. In the former case (fluid phase pinocytosis) , no interactions between the polymer and the cell membrane is assumed and differences in the amount of polymer absorbed by various cells or tissues will reflect differences in their pinocytic activity. In the latter case (adsorptive pinocytosis), the higher concentration of the polymer in the vicinity of the cell surface (i.e. in a layer of a thickness comparable with the vesicle... 

Fig. 11. Modified polyaspartamides for the study of factors modulating the adsorptive pinocytosis of polymers...

Fig. 2. Intracellular trafficking of polymer gene delivery vectors. 1, Internalization (often by adsorptive pinocytosis or receptor-mediated endoc3d sis) 2, escape from endocytic vesicles 3, transport through the cytosol 4, transport across the nuclear membrane. In addition, polyplexes must be unpackaged at some point in the process, although it is not known where in the process unpackaging occurs.

Hyaluronic acid can be re-incorporated into some cells that synthesize it. This adsorptive pinocytosis occurs with mesenchymal cells, but not with either skin fibroblasts or arterial smooth-muscle cells. cAMP appeared to stimulate the synthesis of hyaluronic acid by human fibroblasts and confluent rat fibroblasts. ... 

The uptake of j3-D-acetamidodeoxyglucosidase by cells and the intracellular fate and metabolic effect of this enzyme have been investigated with fibroblasts from normals and from patients with Sanfillipo B syndrome. The uptake for both genotypes was specific, highly efficient, and constant over a period of at least six days the enzyme may be taken up by adsorptive pinocytosis, and evidence was presented for the localization of the pinocytosized enzyme in the lysosomes. The results were evaluated with regard to enzyme-replacement... 

Imidazole-containing polymers designed on the basis of histidine have been reported to have a proton-sponge property and enhanced release of complexes into the cytoplasm following adsorptive pinocytosis [62]. 

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