Cellular surface

Screening the molecular heterogeneity of receptor expression in endothelial cell surfaces is required for the development of vascular-targeted therapies. First, as opposed to targeting purified proteins as discussed above, membrane-bound receptors are more likely to preserve their functional conformation, which can be lost upon purification and immobilization outside the context of intact cells. Moreover, many cell surface receptors require the cell membrane microenvironment to function so that protein-protein interaction may occur. Finally, combinatorial approaches may allow the selection of cell membrane ligands in a functional assay and without any bias about the cellular surface receptor. Therefore, even as yet unidentified receptors may be targeted. 

Blue colour ring concentrated on plasmalemma of pollen (A). Arrows on B (lower part) shows a difference in the colour between cellular surface (blue color) and apperture for the output of pollen tube (red colour). Pistil excreted blue colour product, which covers the red coloured surface of pistil. The cholinesterase activity in plants is considered as sensitive test to study the allelopathic activity (Roshchina and Roshchina 1993 Roshchina,1999 2001a). 

Fig. 4 Fragment of reconstructed part of cellular surface in microspore of Equisetum arvense... 

It is well known that when solid food is immersed in a hypertonic solution, a driving force for the diffusion of water from the food into the solution is set up because the food cellular surface structure acts as a... 

Fullerene showed antibacterial activity, which can be attributed to different interactions of C60 with biomolecules (Da Ros et al., 1996). In fact, there is a possibility to induce cell membrane disruption. The fullerene sphere seems not really adaptable to planar cellular surface, but for sure the hydrophobic surface can easily interact with membrane lipids and intercalate into them. However, it has been demonstrated that fullerene derivatives can inhibit bacterial growth by unpairing the respiratory chain. There is, first, a decrease of oxygen uptake at low fullerene derivative concentration, and then an increase of oxygen uptake, which is followed by an enhancement of hydrogen peroxide production. The higher concentration of C60 seems to produce an electron leak from the bacterial respiratory chain (Mashino et al., 2003). 

Regarding the mechanism of biomolecules functionalized CNTs entering into cells, endocytosis mechanism may be responsible for the phenomena, a theory model is also suggested (Gao et al., 2005) the optimal size of particles entering into cells is between 20 nm and 700 nm or so, too small nanopaiticles are very difficult to enter into cells because of cellular surface tension force and adhesion. The further mechanism of effects of CNTs on human healthcare and environment is being investigated from the following four scales such as molecular, cellular, animals, and environment levels. 

In situ models are to evaluate absorption or membrane permeability under the physiologically relevant tissue condition. While the luminal environment can be modulated by the administered solution, the tissue condition is physiologically controlled. The estimated membrane permeability can be, in most cases, assumed to represent the transport across the epithelial cell layer at steady state or quasisteady state. However, one needs to be aware that the involvement of metabolic degradation, which may occur at the cellular surface or within the cytosol, can be a factor leading to biased estimates of membrane permeability and erroneous interpretation of the transport process. Particularly,... 

Fig. 2. Effect of calcium antagonists (CA) on a cardiac cell. Top typical cardiac action potential. The calcium (slow) inward current flows during the characteristic plateau phase (phase 2) of the action potential. This calcium influx is selectively inhibited by CA. Activation of the sarcoplasmic reticulum (SR) and other cellular calcium pools occurs via Ca + and Na+ ions which flow into the cell. The SR and other pools donate activator Ca + ions which stimulate the contractile proteins. The presence of tubular systems (invaginations), which are characteristic of cardiac tissues, results in considerable enlargement of the cellular surface, thus enabling an effective influx of Na+ and Ca + ions. Inhibition of the calcium inward flux by a CA causes diminished activation of the contractile proteins.

As mentioned in Sect. 2.2.3, the biodistribution of HPMA copolymers depends on many factors. Molecular weight influences the uptake in the isolated tissue of yolk sac [266] as well as the elimination in vivo [124, 125,267,268]. Nonspecific increase in the rate of polymer uptake can be achieved by incorporation of positively charged or hydrophobic comonomers into the HPMA copolymer structure, such as methacryloyloxyethyltrimethylammonium chloride [22], N-methacryloyltyrosinamide [21], or N-[2-(4-hydroxyphenyl)ethyl]acrylamide [267]. The incorporation of hydrophobic moieties may influence the solution properties of the HPMA copolymer conjugates [132,134,269]. The interaction with the cellular surface may depend on the association number and the stability of the micelles. 

Successful gene delivery by use of cationic liposomes requires the following conditions (134) (1) condensation of DNA into the complex and its protection from degradation by intracellular nucleases (2) adhesion of DNA-lipid complex onto the cellular surface (3) complex internalization (4) fusion of an internalized DNA-cationic liposome complex with the endosome membrane (5) escape of DNA from the endosome (6) entry of DNA into the nucleus followed by gene expression. 

Studies of stem cell progression towards the completely differentiated mature cells have already identified several intermediary precursors, organized in a cascade (Shizuru et al., 2005). The best known and studied cellular differentiation cascade is the hematopoietic system (Figure 20.3). Within hematopoiesis, it is possible to identify many intermediary precursors between the hematopoietic stem cell and mature blood cells. This identification is based mainly on the phenotypic profile of cellular surface proteins, using flow cytometry as the main tool. This is a relatively simple technique that involves coupling a monoclonal antibody (mAb) with a fluorescent marker (fluorochrome). In this way, diverse cellular markers can be combined and thus a cellular subpopulation can be defined, as shown in Figure 20.3. 

The a-dispersion is presently the least clarified. Intracellular structures, such as the tubular apparatus in muscle cells, which connect with the outer cell membranes, could be responsible in all such tissues which contain such cell structures. Relaxation of counterions about the charged cellular surface is another mechanism suggested by us. Last, but not least, relaxational behavior of membranes per se, such as reported recently for the giant squid axon membrane, can account for it (2). The relative contribution of the various mechanisms varies, no doubt, from one case to another and needs further elaboration. 

Studies on cellular surfaces. Trypsin leads to loss of surface proteins including glycoproteins and other antigens and it is these changes which presumably lead to cell death when trypsinisation is prolonged. 

Olear T, Nouza K. Thrombin and trypsin receptors The same mechanism of signaling on cellular surfaces. Bratisl Lek Listy 1999 100 75-79. 

Simple mathematical calculations by the first pharmacologists in the 1930s indicated that structurally specific drugs exert their action in very small doses and do not act on all molecules of the body but only on certain ones, those that constitute the drug receptors. For example, Clark [407] calculated that ouabain applied to the cells of the heart ventricle, isolated from the toad, would cover only 2.5% of the cellular surface. These observations prompted Clark [407,408] to apply the mathematical approaches used in enzyme kinetics to the effects of chemicals on tissues, and this formed the basis of the occupancy theory for drug-receptor interaction. Thus, pharmacological receptor models preceded accurate knowledge of receptors by many years. 

Neuraminidase inhibitors prevent the release of influenza A and B viruses. Normally, the viral neuraminidase splits off N-acetyl-neuraminic (sialic) acid residues on the cellular surface coat, thereby enabling newly formed viral particles to be detached from the host cell. Zanamivir is given by inhalation oseltamivir is suitable for oral administration because it is an ester prodrug. Possible uses include treatment and prophylaxis of influenza virus infections. 

Fig. 2 Membrane topology models for the MDR-related ABC transporters. Bars represents predicted transmembrane helices, the circles represents the ABC domains, the tree are glycosylation sites at the extra cellular surface. (Reproduced from [4])...

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