Contact inhibition of movement

This is the situation with BHK 21 hamster fibroblasts (Macpher-son and Stoker, 1962 Stoker and Macpherson, 1964) which still have the correct diploid chromosome number but which are believed to have the incorrect chromosome complement. These cells do, however, exhibit a certain amount of contact inhibition of movement ( 2.4.2) and may be further transformed by treatment with polyoma virus (e.g. to form Py Y cells Fig. 2.1) or SV40 (to form SV28 cells). 

Primary cells will continue or start to divide in culture but exhibit contact inhibition of movement (Abercrombie and Heaysman, 1954). When two such cells approach one another the characteristic ruffling movements of the cell membrane stop in the area of contact. Primary cells therefore do not grow one on top of the other and, in general, cease to divide when a monolayer has been formed. This phenomenon is not restricted to primary cells but applies also to many cell lines. An ideal example is the 3T3 mouse fibroblast cell line which grows rapidly in sparse culture but all division stops as soon as the cells become confluent at about 106 cells per 6 cm dish (Holley and Kieman, 1968). Such cells may for some time remain... 

Let us consider some peculiarities of local corrosion of metals in contact with polymers stimulated by changes (inhibition or acceleration) of corrosion processes at the metal-polymer interface. These changes can be attributed either to a limited velocity of movement of the substances participating in the corrosion process or to chemical and electrochemical effects of the polymer on the metal and their influence on the corrosive media activity. 

Conceptual description of an avascular tumor growth model. Tumor growth is represented as a layered structure consisting of an outer proliferating rim, quiescent band, and necrotic core. The model treats the proliferating, quiescent, and necrotic cells as a continuum under the influence of environmental factors such as nutrient/growth factors from underl)dng tissues, and cell movement in terms of migration and contact inhibition. 

Linear diffusion satisfactorily describes the transport mechanism for a single population. For interacting populations, linear diffusion terms imply that the populations are able to mix completely, with the movement of one cell type unaffected by the presence of cells of the other type. The reality is exactly the opposite. Cell movement is typically halted by contact with another cell. This phenomenon is known as contact inhibition and is very well documented for many types of cells. Sherratt introduced a phenomenological model to account for contact inhibition [402]. Consider the interaction between normal and tumor cells with concentrations pm(xj) and Pt(x, t), respectively. The overall cell flux of both populations is given by x(Pn + Pt)- a fraction Pn/(Pn + Pt) of this flux corresponds to normal cells, so that the flux of normal cells is - [pn/(Pn + Pr)] x(Pn + Pr)> a similar expression for the flux of tumor cells. These expressions indicate that the movement of one population is inhibited by the presence of the other. The system of dimensionless reaction-diffusion equations reads [402]... 

Even with adequate cleaning procedures it is still necessary to ensure that the inhibitor reaches all parts of the metal surfaces. Care should be taken, particularly when first filling, a system, that all dead ends, pockets, crevice regions, etc., are contacted by the inhibited fluid. This will be encouraged in many systems by movement of the fluid in service but in nominally static systems it will be desirable to establish a flow regime at intervals to provide renewed supply of inhibitor. 

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