Mechanism of Polymer Storage in Cells

Pinocytosis seems to be the main if not the only way in which a synthetic water-soluble polymer can enter an intact cell As almost all mammalian cells have developed a pinocytic function through which they can take many important metabolites they all can also capture synthetic polymers together with the surrounding fluid. The rate of polymer uptake by a particular cell is determined by the polymer concentration in the surounding medium and by the size and the rate of formation of pinocytic vesicles by the cell 

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 

The reticuloendothelial system (RES) as a part of the host defense mechanism for the clearance of foreign macromolecules and particles includes several types of macrophages, which are mobile cells with particularly prominent endocytosis, able to transport endocytosed substances from the inner compartments by active motion. Kupffer cells of liver (Fig. 7, 9), reticulocytes of spleen and bone marrow, etc. are other components of RES which are in direct contact with blood. The cells of RES are responsible for a major part of the polymer accumulation from the central compartment 

It is not only the polymer circulating in the blood and lymph which can participate in the formation of the intracellular depo. The epithelial cells of kidney tubules are a very important part of the intracellular compartment (Fig. 5 b). The primary filtrate formed during ultrafiltration through the capillary wall of the, glomerulus is further processed in the tubulus (tube-like structures with walls consisting of a monolayer of epithelial cells) at the end of which the concentrated urine is collected. In the tubulus, mainly in the part proximal to the glomerulus, more than 99 % of the fluid filtered in 

3 Effect of the Natiu-e oi the Polymer and tihe Route of Admiatsteation on the Polymer Fate in the Body 

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