Endocytosis methods

Classical gene transfer methods still in use today are diethylamino ethyl (DEAE)-dextran and calcium phosphate precipitation, electroporation, and microinjection. Introduced in 1965, DEAE-dextran transfection is one of the oldest gene transfer techniques [2]. It is based on the interaction of positive charges on the DEAE-dextran molecule with the negatively charged backbone of nucleic acids. The DNA-DEAE-dextran complexes appear to adsorb onto cell surfaces and be taken up by endocytosis. 

The calcium phosphate method was first used in 1973 to introduce adenovirus DNA into mammalian cells [3]. DNA-Calcium-phosphate complexes are formed by mixing DNA in a phosphate buffer with calcium chloride. These complexes adhere to the cell membrane and enter the cytoplasm by endocytosis. Disadvantages of DEAE-dextran and calcium phosphate transfection are a certain level of cytotoxicity, a complicated transfection procedure, and the fact that not all cell types can be transfected using these methods. 

Hydration of phospholipid head groups is essential properties not only for stabilizing bilayer structures in an aqueous environment, but also for fusion or endocytosis of biological membranes including protein transfers [33-35]. Hydration or swelling behavior has only been studied by indirect methods such as X-ray diffraction [36], differential scanning calorimetry (DSC) [37], and H-NMR [38,39]. 

The use of pulse-chase methods identifies differences in the timing and efficiency of absorption between the two pathways, enabling the study of uptake in the endocytosis system [83]. 

A good approach to study endocytosis is a combination of flow cytometry with a microscopic method such as spectral bio-imaging or confocal microscopy. 

Receptor-mediated endocytosis may be possible because receptors have a high affinity for BDNF (Deckner et al. 1993). A linear relation between intranasal administration of -labeled NGF and brain concentrations of the compound suggest that this transportation is not mediated by receptors and that this releasing method of agents to the brain via olfactory nerves may be effective for many therapies (Frey et al. 1995). BDNF and the insulin-type growth factor (IGF-1) are currently used in clinical studies (Appel 1997). 

Pasyaka N (1997) Use of Enterosgel for correction of endocytosis in children of early age suffering from severe form of acute pneumonia. In Biosorption methods and preparations in prophylactic and therapeutic practice. First Conference, Kyiv (In Ukrainian), p 57... 

As of this writing (ca 1993) there are eight methods of erythrocyte entrapment. Six methods depend on loading via hypotonic exchange, one method dc icnds on chlurpromazine-induced endocytosis. and one depends on voltage-step induced transitory permeation,... 

Leamon, C.P., and P.S. Low. 1991. Delivery of macromolecules into living cells A method that exploits folate receptor endocytosis. Proc Natl Acad Sci USA 88 5572. 

Certain cells have the ability to transport substances across their membranes through processes such as endocytosis. Here the drug is engulfed by the cell via an invagination of the cell membrane. Although limited in scope, this method does allow certain large, nonlipid-soluble drugs to enter the cell. 

Cells do have other transport options. Very small molecules can filter through the various channel proteins in the membrane. Drugs tend to be too large to pass by this method. The filtration of water is specifically called osmosis. Endocytosis is another method by which molecules may enter a cell. Endocytosis comes in many forms, all of which involve the indentation of a section of cell membrane that pinches off to form a new internal vesicle in the cell (Scheme 3.2). Once the cell breaks down the vesicle, the contents are released... 

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